ASTRO-PHYSICS 900GTO User manual

1
ASTRO-PHYSICS
900GTO GERMAN EQUATORIAL WITH
GTOCP3 SERVO MOTOR DRIVE
MODEL 900GTO PARTS LIST 3
FEATURES AND SPECIFICATIONS 4
INTRODUCTION 5
Why Polar Alignment is Important 5
ASSEMBLY INSTRUCTIONS 6
Before You Leave Home 7
Gross Latitude Adjustment 7
Assemble Pier (purchased separately) 9
Attach Pier Adapter to Pier Post 9
Standard Pier Adapter (900SPA) 10
Precision Adjust Rotating Pier Adapter with Azimuth Bearing (900RPA) 10
Hi-Lo Latitude Wedge Pier Adapter Assembly for 0 - 20° or 68° - 88° Latitude – North or South
(900WDGA) 11
Assemble Polar Axis Assembly to Pier or Tripod 11
Altitude and Azimuth Adjustments - Rough polar alignment 12
Assemble Declination Axis 13
Removing Declination Axis at the End of your Observing Session 13
Attach Counterweight Shaft and Counterweights 15
Attach Mounting Rings (purchased separately) 15
Fine Polar Alignment 16
Methods for fine polar alignment 16
Altitude and Azimuth Adjustments 16
CLUTCH KNOBS AND BALANCING 16
R.A. and Dec. Clutch Knobs 16
Balancing Your Telescope 17
First, Balance the Declination Axis. 17
Second, Balance the Polar Axis 17
SERVO MOTOR DRIVE 18
GTO Control Box – GTOCP3 18
R.A. and Dec. Cable Connections 18
12V Connector 19
POWER Indicator Light 19
KEYPAD Connector 19
RS-232 Connectors 19
FOCUS Connector 20
RETICLE Connector 20
AUTOGUIDER Connector 20
+6V Connector 20
N and S Switch 20
Drainage Holes 20
Pre-loaded PEMPro Curve 20

2
Prevent the Cables From Tangling 21
900 Motor Cables 21
Accessory Cables 21
Removing the GTO Control Box from the 900GTO Mount 22
GTO KEYPAD CONTROLLER OPERATION 22
SLEWING YOUR MOUNT IN BELOW FREEZING TEMPERATURES 22
MOUNT CARE,CLEANING AND MAINTENANCE 23
Care 23
Cleaning and Touch-up 23
Mount Maintenance 24
ADDITIONAL TIPS AND SUPPORT 24
TROUBLESHOOTING 24
RECOMMENDED READING FROM OUR STAFF: 26
STANDARD PIER ADAPTER FOR THE 900GTO MOUNT 27
USEFUL DIMENSIONS FOR OBSERVATORY PLANNING 28
CLUTCH PLUG REPLACEMENT FOR 900 OR 1200 MOUNT 29
Construct Your Own Clutch Plug Extraction Tool 30
CHARACTERIZING THE DEC AXIS MOTIONS 30
CHARACTERIZING THE DEC AXIS MOTIONS 31
ASTRO-PHYSICS MOUNTING PLATE FASTENER CHART 32
PLEASE RECORD THE FOLLOWING INFORMATION FOR FUTURE REFERENCE
MOUNT SERIAL NUMBER: ______________________________
KEYPAD SERIAL NUMBER: ______________________________
GTOCP3 SERIAL NUMBER: ______________________________
PURCHASE DATE: ______________________________

3
ASTRO-PHYSICS
900GTO GERMAN EQUATORIAL WITH
GTOCP3 SERVO MOTOR DRIVE
MODEL 900GTO PARTS LIST
1 Polar axis assembly (right ascension-R.A.) with GTO Control Box (Model GTOCP3)
1 Declination (Dec.) axis assembly
1 14” Stainless counterweight shaft (1.875” dia.) with machined, black-anodized, safety stop
1 Y cable – R.A. portion is 15.25” long and Dec portion is 40.25” long
1 D.C. power cord (cigarette lighter adapter on one end) - 8’ long
1 GTO Keypad controller with 15’ coiled cable and Instruction Manual
1 PEMPro™ v.2 – Full Version - Periodic Error Management software for Astro-Physics mounts (CD-ROM)
1 PulseGuide™ by Sirius Imaging – remote control utility for improved guiding (CD-ROM)
1 Hex key set
2 8-32 Thumbscrews (substitute for set screws to allow quick disconnect of GTO control box)
In order to assemble your mount fully, you will need the following items sold separately:
•Telescope mounting plate – many choices to fit your telescope and observing needs.
•20° to 68° latitude: choose either the Standard Pier Adapter (900SPA) or the Precision Adjust Rotating Pier
Adapter with Azimuth Bearing (900RPA). Either adapter will come with six 5/16 – 18 X 5/8” button head
screws for attachment to the pier, four pier knobs for attaching the mount to the adapter, and the azimuth block
for use with the Heavy Duty Azimuth Adjuster found on all 900GTO mounts produced after August, 2005 and
available as an upgrade for earlier mounts.
•Tropical or extreme polar latitudes (0° to 20° or 68° to 88° North or South): choose the Hi-Lo Latitude Wedge
Pier Adapter Assembly (900WDGA) Also – see below.
•8” O.D. pier – Astro-Physics has several heights and styles to choose from.
•Counterweights – 5 lb. (5SCWT), 10 lb. (10SCWT) and 18 lb. (18SCWT) are available.
•Power supply. We offer 2 power converters (PS138V5A) and (PS15V10A) for converting household current to
suitable DC current for your mount. Rechargeable 12 volt battery packs and deep cycle marine batteries are
also available from other vendors.
Many of these items will be discussed throughout these instructions. Several additional options are available:
•Polar Alignment Scope with Illuminator (PASILL4) – for quick and easy polar alignment
•Pier accessory trays (TRAY08) and (TRAY08H) for 8” pier and support bars (TRAYSB) or (TRAYSB1) - handy
to keep your eyepieces and other accessories close at hand!
•Longer counterweight shaft (M12601-C) – 19.5” (18.5” usable) stainless steel shaft
•9” counterweight shaft extension (M12675)
•Hi-Lo Latitude Wedge (900WDG) – for those who already own one of our other adapters - allows use from
tropical or polar latitudes: (+/- 0° to 20° or +/- 68° to 88°). Use the knobs & washers, azimuth adjuster block
and center pivot screw from the other adapter. Complete Wedge Assembly is part # (900WDGA).
•900 Flat Surface Adapter (900FSA) – for attaching one of our pier adapters to your own custom pier or tripod.
•Losmandy Tripod Adapter (LT2APM) – for attaching 900GTO to Losmandy Heavy Duty Tripod or Losmandy MA
Meade Field Tripod Adapter.
•Santa Barbara Instrument Group CCD Imaging cameras, STV, ST-4 Autoguider or other imaging camera- if you
plan to pursue CCD imaging or astrophotography
For a complete listing of our 900GTO accessories, visit our website – www.astro-physics.com
Note on Encoders: Mounted encoders can no longer be used with the 900GTO (for mounts shipped starting in October,
2005 – beginning serial number 900451) because of the R.A. shaft re-design. They are not needed since the go-to
functions of the mount are so much more accurate. The encoder that is built into the servo motor itself has a resolution of
0.05 arc seconds vs. 324 arc seconds for mounted encoders.

FEATURES AND SPECIFICATIONS
R.A. worm wheel: 7.2”, (18.3 cm) 225 tooth aluminum
Dec. worm wheel: 6”, (15.2 cm) 225 tooth aluminum
Worm gear: Brass
R.A. shaft: 2.2”, (5.6 cm) diameter
R.A. thrust surface: 7.0”, (17.8 cm) diameter
Dec. shaft: 1.75”, (4.4 cm) diameter
Dec. thrust surface: 6.0”, (15.2 cm) diameter
Counterweight shaft: 14”, (35.6 cm) overall, 13”, (33.0 cm) useable length, 1.875”, (4.8 cm) diameter,
stainless steel, removable
Latitude range: 20 to 68 degrees with or without polar scope attached. You can achieve
higher or lower latitudes with our Hi-Lo Latitude Wedge Assembly (900WDGA) or Hi-Lo
Latitude Wedge (900WDG)
Azimuth adjustment: Approximately 15 degrees
Setting circles: Porter Slip Ring design, engraved
Right ascension: 4-minute increments, pointer, engraved both north and south
Declination: 1-degree increments, pointer
Motors: Zero-cogging servo motors
Power Consumption: 0.4 amps at the sidereal rate
2 amps both motors slewing
Power requirements: 12 VDC, range 11.5 to 16
Weight of mount: Total -54 lbs. (24.5 kg)
Dec axis - 17 lbs. (7.7 kg)
R.A axis - 26.5 lbs. (12.0 kg)
Counterweight shaft with safety stop -10.5 lbs. (4.8 kg)
Capacity of Mount: Approximately 70 lbs. (31.8kg) - telescope and accessories (not including
counterweights), depending on length. Will accommodate Astro-Physics and similar
refractors up to 180mm f9, 12" Cassegrains, 12-14" Ritchey-Chretiens. These are only
guidelines. Some telescopes are long for their weight or very heavy for their size and
will require a larger mount. Note: As weight of scope and accessories increases,
proper balancing becomes more critical. See section on balancing for more
information.
4

INTRODUCTION
The 900GTO German equatorial was designed to meet the needs of the advanced observer who requires a mount with
maximum strength and rigidity and minimum weight. The excess material in both axes has been carved out while retaining a
heavily ribbed structure for internal strength and rigidity. A unique dovetail was machined into the mating surfaces of the R.A.
and Dec axes. This feature allows quick and easy assembly in the field without any tools.
The DC servo motor drive with GTO computer system, the keypad with its digital display screen, and the included
PulseGuide™ and PEMPro™ v.2 software all combine to offer extraordinary sophistication for today’s observer. Whether
you enjoy visual astronomy exclusively or plan an aggressive astrophotography or CCD imaging program, this mount will
allow you to maximize your night out under the stars.
The advanced keypad features allow you to slew automatically to objects in a wide range of databases as well as any
R.A./Dec coordinate. A large selection of common names for stars and other objects makes your selection a snap. The rapid
slew rate of 5 degrees per second (1200x) allows you to locate objects very quickly and accurately. You will be very pleased
with the intuitive operation of this keypad. There are no complicated sequences of keystrokes to remember. It is so easy to
use that even if you don’t use it for a few months, you will feel at home with the keypad very quickly.
PulseGuide™ is a stand-alone Windows (98, ME, 2000, NT4, XP, Vista) utility that provides complete remote control of all
Astro-Physics GTO mounts. It derives its name from its most distinctive feature, pulse guiding, which can improve unguided
tracking. Specifically, it can help correct tracking errors caused by polar misalignment and atmospheric refraction. You can
also train PulseGuide™ to track objects moving relative to the stars, such as asteroids, comets, and the moon. In addition to
pulse guiding, PulseGuide™ also has many useful utility features. PulseGuide™ was written by Ray Gralak of Sirius-
Imaging. Please refer to his website http://www.pulseguide.com for further developments and enhancements.
PEMPro™ (Periodic Error Management Professional) is a Windows software application that makes it easy to characterize
and reduce periodic error. PEMPro™ will analyze the performance of any mount that is equipped with a CCD camera and
compatible camera control software. PEMPro™ gives you powerful tools to program your mount's periodic error correction
firmware to achieve the best possible performance for your mount. PEMPro™ dramatically improves guided and unguided
imaging resulting in better images and fewer lost exposures. PEMPro™ v.2 Full Version also adds a Polar Alignment Wizard
and a video interface for using many webcams. PEMPro™ v. 2 Full Version began shipping with 900GTO mounts in May,
2008.
The periodic error of your 900GTO will be 7 arc seconds or less (before correction). We have already loaded the PEMPro
curve that was generated during your mount’s testing into the servo to reduce the error even further, and to give you a head
start right out of the box. See additional information under “Servo Motor Drive.”
The 900 is equally at home in a permanent observatory or as a portable mounting for remote star parties thanks to the ease
with which the two axes come apart. This is the perfect mount for a mid-size refractor, Newtonian, Cassegrain or astrograph.
In order to maximize your pleasure on your first night out,
we recommend that you familiarize yourself with the
assembly and basic operation of the mount indoors. The
temperature will be comfortable, the mosquitoes at bay,
and you'll have enough light to see the illustrations and
read the manual. Please take particular note of counter-
balancing, use of the clutches and operation of the
keypad controller.
Why Polar Alignment is Important
Polar alignment compensates for the Earth’s rotation.
If you were to take a long exposure photograph with
Polaris (often called the North Star) in the center of the
field, you would discover that all stars seem to revolve
around Polaris. This effect is due to the rotation of the
earth on its axis. Motor driven equatorial mounts were
designed to compensate for the earth's rotation by
moving the telescope at the same rate and opposite to
the earth's rotation. When the polar axis of the telescope
is pointed at the celestial pole (polar aligned) as shown
in the diagram, the mount will follow (track) the motions
of the sun, moon, planets and stars. As a result, the
object that you are observing will appear motionless as
you observe through the eyepiece or take astrophotos.
5

ASSEMBLY INSTRUCTIONS
Please read all instructions before attempting to set up your 900GTO mount. The model 900 is very rugged, however like any
precision instrument, it can be damaged by improper use and handling. Please refer to the following illustrations. The parts
are labeled so that we can establish common terminology.
NOTE: The following terms and abbreviations are used interchangeably in these instructions:
polar axis = right ascension axis = R.A. axis = R.A. housing
declination axis = dec. axis = dec. housing
6

Before You Leave Home
Since most of us must set up our instruments in the dark, in the cold or while battling mosquitoes, a bit of preplanning and
organization is important. There are a few simple things that can be accomplished in the comfort of your home before
heading outside.
Gross Latitude Adjustment
The latitude range of the 900 mount is approximately 20-68 degrees. Since most astronomers typically observe within one
latitude range, this first adjustment is made just once, if at all. Prior to shipment, we preset the mount to your latitude range
for your convenience. If you travel to another observing location, determine the latitude of your observing site and make the
appropriate adjustment. If you live in or plan to travel to tropical locations that are 0 to 20 degrees latitude north or south, or
extreme polar sites that are between 68 and 88 degrees north or south, we recommend our Hi-Lo Latitude Wedge Pier
Adapter Assembly (900WDGA). Pier Adapters are discussed fully later in the manual.
The four positions for the altitude adjustments have the following approximate ranges:
52 degrees to 68 degrees latitude - top position
41 degrees to 59 degrees latitude - third position
30 degrees to 45 degrees latitude - second position
20 degrees to 34 degrees latitude - bottom position
How to change the position of the altitude adjuster
1. Use only the R.A. axis. DO NOT
attempt to make these adjustments with
the declination axis in place and
certainly not with an instrument fully
mounted.
2. Loosen both altitude-locking knobs
about 1 turn.
3. Locate the side of the polar axis that
does not have the black motor/gear
housing box. Loosen (about 1 turn) the
polar axis pivot screw and altitude
adjuster bar fixing screws on this side
only. With your hand, push the polar
axis upwards so that the altitude-locking
knobs are positioned at the top of the
altitude adjustment slot (this is the
maximum altitude position). Some
resistance will be felt with this operation
as you are pushing against the weight
of the polar housing and the
resistance of the remaining polar
axis pivot screw (which has not
been loosened).
4. Before attempting to move the
altitude adjuster bar, you must
tighten the altitude-locking knob on
the motor/gear housing side. This
will prevent any downward
movement of the polar axis during
positioning of the altitude adjuster
bar.
5. While supporting the altitude
adjuster bar, remove the two
altitude adjuster bar fixing screws
that support it on each side (4
screws in all), but keep the two
ends of the bar in contact with the
side of the mount, don't remove it completely (this tip is for your convenience).
7

6. Determine the latitude range that you need and position the altitude adjuster
bar so that the hole that is marked “A”, as shown in the diagram, is located
at the appropriate hole position numbered 1-4 in the lower diagram. Note
that hole “A” is located at the rounded part in the center of the altitude bar.
Hole “A” is the “latitude hole.”
7. Attach two of the screws (one on either side of the adjuster bar) through the
appropriate altitude adjustment position hole and into hole A of the adjuster
bar, but do not tighten. Rotate the altitude adjuster bar around this pivot
point until the corresponding hole lines up. Consult the labeled photo to
determine which hole of the altitude adjuster bar should be used. Be very
careful since the holes marked C and B are very close to one another, as
are the holes marked D and E. The incorrect hole may appear to line up,
however it will be slightly off. If you try to attach at the incorrect hole, you
may strip the threads of the altitude bar. The correct hole will orient the
adjuster to be roughly perpendicular to the axis once the axis is lowered into
place.
8. Once you have located the correct hole, insert the remaining two screws, and lightly tighten so that you still have
some ability to wiggle the bar.
9. Note that the altitude adjustment knob is attached to a
threaded rod that travels through the altitude adjuster
bar. Turn the knob so that the altitude adjuster bar is
positioned approximately in the middle of the threaded
rod. You should see about half of the threaded rod
protruding from both sides of the altitude adjuster bar.
This will allow you to move the mount fully within the
altitude range.
10. At the end of the threaded rod mentioned in the last
step, you will see a small brass altitude adjuster thrust
pad. This is the part that will come in contact with the
polar axis as you ease it back into position. Loosen the
altitude-locking knob (motor/gear side) and lower the
polar axis so that it rests comfortably on this pad. The
threaded rod should be positioned at a right angle to the
polar axis housing. Firmly tighten the altitude adjuster
bar fixing screws.
11. Turn the altitude adjustment knob to raise or lower the
polar axis to your approximate observing latitude.
Tighten the altitude locking knobs with finger pressure
only. You do not need to tighten with the hex key.
12. Firmly tighten
both polar axis pivot screws with the hex key.
8

Assemble Pier
(purchased separately)
Begin by assembling the portable pier at the desired
observing location. Note which direction is north.
1. Slide the three legs onto the nubs of the base
and rotate the assembly so that one of the legs
points toward north (or south, if that is your
preference).
2. Place the pier post on the base orienting the
center azimuth block directly north. If you choose
to have one leg north, then the pier adapter plate
will have to be installed with the azimuth block
directly over a turnbuckle. If you have one leg
south, the pier adapter plate will have to be
installed with the azimuth block over and
between two of the pier post turnbuckles.
3. Attach the tension rods. The turnbuckles should
be drawn tight until the whole assembly is stiff
enough to support your weight without
movement.
Attach Pier Adapter to Pier Post
The 900 Standard Pier Adapter (900SPA) was included with 900 mounts sold in the past. However, in 2005, we began
offering three choices: the Standard Pier Adapter (900SPA), the Hi-Lo Latitude Wedge Assembly (900WDGA) for tropical
latitudes (0° to 20° N or S) or polar latitudes (68° to 88° N or S), and the Precision Adjust Rotating Pier Adapter with Azimuth
Bearing (900RPA). You probably added one of these options to your mount order. If you plan to have multiple pier
installations, perhaps one permanent and another portable, you may wish to purchase an extra adapter to install on the
second pier. This will make your setup and switch-over much quicker. Many customers have found this to be advantageous.
If you are constructing your own pier or tripod, you will need to incorporate one of our pier adapters. You may also wish to
purchase our Flat Surface Adapter (900FSA) if your home-made pier has a flat surface on top. All three pier adapters were
designed to fit into an 8" O.D. x 0.125" wall tube with 6 button head screws with washers threaded into the side. The
Standard Pier Adapter can also be bolted onto a flat surface by using the four countersunk thru-holes. The Rotating Pier
adapter, the Hi-Lo Latitude Wedge and pier adapters from earlier production runs do not have the thru-holes. They require
the Flat Surface Adapter for mounting onto a flat surface. Note that with the Astro-Physics pier, you can orient the pier
adapter so that one of the pier legs faces "north" or "south" as you prefer. If you need an extra Pier Adapter for a second
pier, they are available for purchase.
If you did not purchase one of our pier adapters described below - for instance, if you purchased the Monolith Pier from
Particle Wave Technologies, you will need to purchase the Pier Adapter Knob Kit (part# 9KBKIT) in order to attach your
mount to the Pier. Additionally, outside manufacturers may not provide the Azimuth Adjuster Block (M12020-A) or the
center pivot screw (M12330M). Both of these parts are vital to the
correct performance of your mount (see note on center pivot below) and
can be purchased by calling Astro-Physics.
Important notes for all three pier adapters or when using the
Monolith Pier :
•The washers for the pier adapter knobs must be positioned with
the smooth surface and rounded edge down so that the
assembly can be adjusted back and forth.
•Do NOT remove the center pivot screw. Just as the name
implies, this is the point around which the mount rotates (pivots) when making azimuth adjustments. The screw
head has been machined to assure a close fit. Please do not replace it with another screw.
9

Standard Pier Adapter (900SPA)
This 900 Pier Adapter is similar to those that we have included with mounts in the past, however the azimuth adjuster block
is slightly taller to accommodate the improved azimuth adjuster assembly on all 900GTO mounts produced after August,
2005 (and all upgraded older mounts). If you have a permanent installation, this base is a good choice since you will not have
to set up every session.
The adapter includes the machined flat plate, four machined aluminum lock knobs with washers, the azimuth adjuster block,
center pivot screw and six 5/16-18 x 5/8 button head screws and washers.
Attach to an Astro-Physics pier: To attach the pier adapter to your Astro-Physics
pier, simply set the adapter into the top of the pier post, make sure the azimuth
adjuster block is on the north side, and fasten from the side with the six screws
and washers provided.
Attach to a flat surface on your own pier: If you are mounting to a flat surface of
your own design, simply use four 1/4–20 stainless steel cap screws of appropriate
length, fastened through the top of your adapter. Refer to the diagram in the
back of the manual for bolt pattern information.
If you prefer a more finished look, you may wish to consider using our 900 Flat
Surface Adapter (900FSA). The Flat Surface Adapter bolts onto the flat plate on
top of your pier or tripod, then the Standard Pier Adapter slips in (just as it fits into
our pier) and you fasten from the side with the six screws and washers provided
with the Standard Pier Adapter. The bolt circle for attaching the 900 Flat Surface
Adapter to your pier is 7.230” diameter.
Using an ATS pier:The O.D. of the plate will need to be modified by ATS for an
additional charge.
Precision Adjust Rotating Pier Adapter with Azimuth Bearing (900RPA)
This pier adapter was designed for very accurate and smooth adjustment of the azimuth angle without loosening the lock-
down knobs on the base of the mount. The top plate of the adapter rotates through the 900GTO mount’s full 15 degrees of
azimuth motion. (It does not rotate through a full 360 degrees!) This Rotating Pier Adapter is the ideal choice for portable
setups as it makes azimuth adjustment so easy. Upgrade your previous model 900 mount (any version) and enjoy the ease
of use. Do a setup, followed by a fine polar alignment at a remote site just once, and you will wonder how you ever got
along without this pier adapter!
The adapter includes two machined flat plates, four machined aluminum lock
knobs with washers, a tall version of the azimuth adjuster block, center pivot
screw and six 5/16-18 x 5/8 button head screws and washers.
Attach to an Astro-Physics pier: Simply fit the Rotating Pier Adapter into
your Astro-Physics Portable Pier just like the Standard Pier Adapter and
fasten it from the side with the six screws and washers provided. Again,
make sure that the Azimuth Adjuster Block is on the north side.
Attach to a flat surface on your own pier: The Rotating Pier Adapter must
fit inside another part and be bolted from the side. It cannot be bolted
through the top as you can with the Standard Pier Adapter. We
recommend our 900 Flat Surface Adapter (900FSA). The Flat Surface
Adapter bolts onto the flat plate on top of your pier or tripod, then the
Rotating Pier Adapter slips in (just as it fits into our pier) and you fasten
from the side with the six screws and washers provided with the Rotating
Pier Adapter. The bolt circle for attaching the 900 Flat Surface Adapter to
your pier is 7.230” diameter.
Using an ATS pier:If you plan to use an ATS pier, the O.D. of the plate
will need to be modified by ATS for an additional charge.
The two recessed screws (3/16 hex), shown by the arrows, adjust the tension between the two plates of the Rotating Pier
Adapter. These are preset to an optimal tension and should rarely, if ever, need to be re-adjusted. You do not need to
tighten or loosen these two screws as part of your normal polar alignment routine.
10

Hi-Lo Latitude Wedge Pier Adapter Assembly for 0 - 20° or 68° - 88° Latitude – North or South
(900WDGA)
If your latitude is between 20° north and 20° south or between 68° and 88°, either north or south, this wedge assembly
includes everything you need to place your 900 mount in the proper position.
This adapter includes the machined wedge and flat plate, the 1.2" Azimuth Adjuster Block, four Pier Adapter Knobs with 1/4"
ID x 1" OD flat washers, the center pivot screw, six 5/16-18 x 5/8 socket buttonhead screws and six 5/16 x 9/16"OD x 0.060"
flat washers, which enable you to attach the pier adapter to your Astro-Physics pier.
Please Note: 1.) If you already own another adapter, the Hi-Lo Latitude Wedge may be purchased alone, without the Pier
Adapter Knobs, Azimuth Block or Center Pivot Screw. (900WDG)
2.) The photo shows the Hi-Lo Latitude Wedge ready to be used at tropical latitudes with the Azimuth Adjuster
Block on the low side. For extreme polar latitudes, the plate on top of the wedge can be turned around to
extend the useful range of your 900GTO above 68° latitude. Simply remove the two side knobs and then
remove the six screws that attach the flat plate to the wedge. Rotate the flat plate 180° and re-assemble with
the Azimuth Adjuster Block on the high side.
Attach to an Astro-Physics pier: To attach the Hi-Lo Latitude Wedge to your
Astro-Physics pier, simply set the adapter into the top of the pier post, make
sure the azimuth adjuster block is on the north side, and fasten from the side
with the six screws and washers provided.
Attach to a flat surface on your own pier: The Hi-Lo Latitude Wedge must fit
inside another part and be bolted from the side. It cannot be bolted through the
top as you can with the Standard Pier Adapter. For custom installations, we
recommend our 900 Flat Surface Adapter (900FSA). The Flat Surface Adapter
bolts onto the flat plate on top of your pier or tripod, then the Hi-Lo Latitude
Wedge Pier Adapter slips in (just as it fits into our pier) and you fasten from the
side with the six screws and washers provided. The bolt circle for attaching the
900 Flat Surface Adapter to your pier is 7.230” diameter.
Using an ATS pier:The O.D. of the plate will need to be modified by ATS for an
additional charge.
Assemble Polar Axis Assembly to Pier or Tripod
In order to track the motion of astronomical objects, the polar
axis must be positioned so that an imaginary line drawn through
the center of the axis points toward the celestial pole. At this
stage of the assembly process, you want to position the pier
and mount so that it points roughly north, if you have not
already done so.
1. Remove the four (4) Pier Knobs on the Pier Adapter
and keep them close at hand.
2. Prior to lifting the polar axis assembly into place, turn
the fine azimuth adjustment knobs so that the space
between them is wide enough to allow the center
azimuth block to fit easily between them. See photo
at right. Ensure both Pier Adapter top and polar axis
assembly mating surfaces are clean and free of dirt.
If you are using the Rotating Pier Adapter, make sure
that the Altitude Adjuster Block is centered in the slot
of the top plate.
3. Place the Polar Axis Assembly onto the Pier Adapter so that the Azimuth Adjuster Block fits between the fine
Azimuth Adjustment Knobs. The Center Pivot Screw on the Pier Adapter (all models) will help you center the
mount on the adapter.
4. Move the base of the polar axis assembly so that the threaded holes of the Pier Adapter top can be seen through
each of the four slots.
5. For the Standard Pier Adapter or 900 Hi-Lo Latitude Wedge, thread the four Pier Knobs loosely in place (you will
tighten these later after polar alignment). For the Rotating Pier Adapter, go ahead and tighten the four Pier Knobs
securely.
11

Altitude and Azimuth Adjustments - Rough polar alignment
For rough polar alignment, your goal is to sight the celestial pole when looking through the polar alignment sight hole in the
center of the polar axis. You will need to make altitude (up/down) and azimuth (side-to-side) adjustments to the position of
the mount.
We recommend that you do your rough polar alignment with the
R.A. axis only since you will be making major adjustments to the
position of the mount at this time. The remainder of the mount,
telescope and counterweights will add considerable weight and
require more hand effort. Later, you will do your final polar alignment
with the telescope and counterweights attached, but the adjustments
will be small.
1. If the Polar Scope (PASILL4) is installed, you may remove
it to complete these steps. Alternatively, you can simply
sight up the side of the polar axis to see Polaris.
2. If you examine the polar axis assembly, you will see that
the center of the R.A. shaft is hollow. If you have the
Standard Pier Adapter or the Hi-Lo Latitude Wedge Pier
Adapter and have not done so already, loosen (1/2 turn)
the four pier knobs. If you have the Rotating Pier Adapter
you do NOT loosen the Pier Knobs.
NOTE: If you have already attached the Dec. axis, remove
the sight hole cover and rotate the internal Dec. shaft by moving the top of the Dec. axis (or the cradle plate if it is
attached) to reveal the sight hole that has been drilled into it. Now, you can look through the shaft to the other side.
3. Azimuth adjustments: To begin with, move or turn the entire pier or tripod east or west until the mount is oriented
approximately towards the pole (an imaginary line drawn through the hollow shaft). Once you are relatively close,
use the two fine azimuth adjustment knobs, one on each side of the mount, to make adjustments. You must back
off the opposing azimuth knob in order to move the other knob in that direction. Please refer to the photos below.
These photos also illustrate the 15 degrees of azimuth adjustment possible with this mount.
One full turn of the azimuth knob is approximately 0.63 degrees (38 arc minutes) Each long
registration mark is about 7.6 arc minutes; each short mark is about 1.5 arc minutes.
When designing the Heavy Duty Azimuth Adjusters for both the 900 and 1200 mounts, we debated using an
azimuth adjuster with a single captured threaded rod passing through a stationary azimuth block to avoid the two
step process of backing off one side, and then adjusting the other. However, we found that the inevitable backlash
in this type of system made adjustment more problematic and less precise. The way to use the Astro-Physics
Heavy Duty Azimuth Adjuster with its clear registration marks for fine adjustment is to back off one of the knobs by
a set amount (a certain number of registration marks) and then to turn the other knob until you re-establish contact
on both sides of the Azimuth Adjuster Block. You can very precisely zero in on the desired position with no
backlash or ambiguity on the position. You can also always go back to the precise starting point if for some reason
you overshot your mark (or if you adjusted the wrong way), because you know exactly how far you’ve gone.
12

4. Altitude (latitude) adjustments: Loosen the altitude locking knobs. Move the polar axis up or down with the large
altitude adjustment knob located in the front of the polar axis assembly. The tommy bar can be positioned in any of
the threaded holes located in the altitude adjustment knob. Use this bar to help you turn the knob. We have found
that using the turnbuckle on the north leg of our pier also can make fine altitude adjustments, if used.
One full turn of the altitude knob is approximately 0.64 degrees (38 arc minutes).
5. Continue your azimuth and altitude adjustments until you can sight Polaris in the polar alignment sight hole. At this
point, you have achieved a rough polar alignment, which may be sufficient for casual visual observations, if you are
not planning to slew to target objects with the keypad. When the R.A. motor is engaged (the power is plugged in), it
will compensate for the rotation of the earth and keep the target object within the eyepiece field of view. Your target
object will slowly drift since polar alignment at this stage is only approximate. However, you can make corrections
with the N-S-E-W buttons of your keypad controller.
6. Tighten the altitude locking knobs by hand.
7. If you are using the Standard Pier Adapter or the Hi-Lo Latitude Wedge, tighten the pier knobs firmly by hand. On
the Rotating Pier Adapter, the knobs will already be tight.
Assemble Declination Axis
1. Do not have your telescope or counterweights
connected to the Dec. axis for either assembly or
disassembly of the Dec. and R.A. axes.
2. Position the R.A. axis as shown in the diagram shown
to the right with the guide notch "A" at the top, opposite
the altitude adjuster knob. Firmly tighten R.A. clutch
knobs.
3. During shipment, the Dec. axis assembly lock knobs will
be fully screwed into the Dec. axis assembly. For
correct assembly, these lock knobs should be
unscrewed at least 7 full turns and no more than 8.5 full
turns. This is between 5/16" and 3/8" out from the
"shipped" tightened position. Note: These lock knobs
can be completely removed from the Dec. axis
assembly with about 9.5 full turns out.
4. Position the Dec. axis above the R.A. axis as shown in
the diagram, a light movement (wiggle) in the downward
direction (arrow "A") will help to correctly seat the
principle dovetail(s) and parallel guides.
5. When both Dec. and R.A. assemblies are fully seated, hand tighten
both Dec. lock knobs.
Removing Declination Axis at the End of your
Observing Session
1. Move the telescope so that the counterweight shaft is pointing
down and the telescope is horizontal (level) and pointing east.
Carefully remove your telescope accessories, then the telescope,
then counterweights, and finally the counterweight shaft.
2. Unscrew the lock knobs 5.5 to 7 full turns (this is still 5/16" to 3/8"
out from the fully tightened position) and slide/tilt the Dec. axis
assembly in an upward direction (arrow "B").
3. For transport/storage we recommend fully tightening the lock
knobs.
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Attach Mounting Plate
(purchased separately)
Several mounting plates (also called cradle plates) are available for the 900GTO
mount. If you own more than one instrument, you may need more than one plate, or
you may wish to use one of the dovetail mounting plate options with more than one
male dovetail sliding bar. Attach your mounting plate with the screws provided with
the plate using one of the hole patterns shown at right. It is important to use the
proper screws, please refer to the instruction sheet entitled “Mounting Plate
Fastener Chart.” This chart is available at the end of this manual and in the
technical support section of our website.
15" FLAT MOUNTING PLATE (FP1500)
This plate is 15" long by 4.6” wide by 0.5” thick. Two pairs of keyhole slots
that measure 3.2" between centers are provided. The pairs are 13.75"
apart. You can drill additional holes to suit your needs. This plate also fits
the Mach1GTO, 400 and 600E German Equatorial mounts.
Attach this plate with four 1/4-20 x 5/8" socket head cap screws
18" FLAT MOUNTING PLATE (FP1800)
This plate is 18" long and 7.5" at its widest point in the center. The
width of the plate tapers to 5.5" at each end. Four pairs of keyhole
slots that measure 3.2" between centers are provided. The two
inner pairs are 13.75" apart and the outer two pairs are 17" apart.
You can drill additional holes to suit your needs. This plate also
fits the Mach1GTO and 1200 German Equatorials.
Attach this plate with six 1/4-20 x 1" flat head socket cap screws.
15” RIBBED MOUNTING PLATE (900RP)
The finished plate is 0.75" thick, 15" long and 6.5" at its widest point. The
width of the plate tapers to 4.75". A pair of keyhole slots that measure 3.2"
between centers are provided at each end. The distance between these
pairs of holes is 13.75". Due to the ribbed structure, you may not be able to
drill additional holes to suit your mounting rings. The plate weighs 2.3 lbs.
Attach this plate with four 1/4-20 x 1" flat head socket cap screws. Note
that the plate is asymmetrical. In most cases, orient the plate so that the
long end points toward the sky. You can also turn the plate in the other
direction to balance your scope.
NOTE: All three of the above plates have a hole spacing of 13.75”. This
allows the use of the 15” dovetail plate (DOVE15) on top of your instrument
as an accessory plate.
8” ASTRO-PHYSICS DOVETAIL MOUNTING PLATE (DOVE08) with Q4047
ADAPTER
This versatile plate is suited for the 105 f6 Traveler and 130 refractors (we prefer the 15" Dovetail
Plate for most applications of the 130 f8 StarFire EDT) and other short instruments. The knob
assembly features a brass pin with a tapered end to hold your sliding bar firmly without marring the
aluminum. Use with the 7” or 10” sliding bars (SB0800 or SB1000), which are sold separately.
Repositioning the sliding bar will aid in adjusting the balance of your instrument.
NOTE: This plate requires the use of the Q4047 adapter with the 900GTO mount to provide clearance
for the knobs.
As an accessory plate - Attach to the top of our Astro-Physics mounting rings (tube diameters 5"-8") or
rings from Parallax Instruments that have the Astro-Physics hole pattern (you can request it). Note, you
must also use a sliding bar on the bottom of the rings with the same distance (6.3" from center to
center), i.e. the SB0800 or SB1000.
Attach the Q4047 to the mount using the six outside holes and six 1/4-20 x 5/8” flat head socket cap
screws. Attach the DOVE08 to the Q4047 with four 1/4-20 x 5/8” socket head cap screws.
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15” ASTRO-PHYSICS DOVETAIL (DOVE15) FOR 15” SLIDING BAR (SB1500)
The 15" version of our dovetail plate is suited for the 130 f8 StarFire
EDT, 155 f7 StarFire EDFS, ARO Maksutovs, Takahashi scopes and
other instruments of similar size. The knob assembly features a brass
pin with a tapered end to hold your sliding bar firmly without marring the
aluminum. Use with the 15" Sliding Bar (SB1500), which is sold
separately (NOT for use with Losmandy “D” plates). Also makes a
great accessory plate when used with either the 900RP, the FP1500 or
FP1800 (with rings mounted to inside holes)
Attach with four 1/4-20 x 5/8” flat head socket cap screws.
8.5” DOVETAIL FOR LOSMANDY D SERIES PLATE (DOVELM2)
This Astro-Physics plate attaches to the 400, 600E, 900, 1200 and Mach1GTO mounts. If you
already own one of the Losmandy DAP series (fits Astro-Physics refractors), DC series (for
Celestron 8" or 9.25” SCTs) or DM series (for Meade 8" and 10" SCTs) plates, you should
consider this plate or the longer DOVELM16S. For larger size SCT’s we recommend the
longer DOVELM16S – see below.
Note that there are two bolt-hole patterns, each offset from the center. This allows you to
position the plate either forward or backward depending on the balance point of your telescope.
Attach this plate with four 1/4-20 x 5/8" socket head cap screws. This plate can also be attached using one 1/4-20 x 5/8” flat
head socket cap screw and one 1/4-20 x 3/4” socket head cap screw using two opposite holes of the declination hub’s six
hole pattern.
16" DOVETAIL FOR LOSMANDY D SERIES PLATES (DOVELM16S)
This Astro-Physics plate attaches to the 900 and Mach1GTO mounts.
If you already own one of the longer Losmandy DAP series (fits larger
Astro-Physics refractors), DC series (for Celestron 8", 9.25" or 11”
SCTs) or DM series (for Meade 8", 10" or 12” SCTs) plates, this is the
mounting plate for you.
Note that the bolt-hole pattern is offset from the center. This allows
you to position the plate either forward or backward depending on the balance point of your telescope. Attach this plate with
four 1/4-20 x 1" socket head cap screws. This plate can also be attached using two 1/4-20 x 1” socket head cap screws
using two opposite holes of the declination hub’s six hole pattern.
Attach Counterweight Shaft and Counterweights
IMPORTANT: Always attach the counterweights before mounting the telescope to the
cradle plate to prevent sudden movement of an unbalanced tube assembly, which may
cause damage or injury. Remember counterweights are heavy and will hurt if they fall on
your foot.
1. Thread counterweight shaft onto the Dec. axis. Turn it snug, but DO NOT overtighten!
2. Remove the one piece safety stop from the base of the counterweight shaft. Add sufficient counterweights (5, 10 or
18 lb. counterweights must be purchased separately) to the counterweight shaft to balance the telescope you
intend to use. Always use two hands to attach or move them on the shaft.
3. Reattach the safety stop to the end of the counterweight shaft. This will help to prevent injury if someone
accidentally loosens the counterweight knob.
NOTE: A firm tightening of the counterweight knob will not damage the surface of the counterweight shaft. The pin that
tightens against the stainless counterweight shaft is constructed of brass. Likewise, the bronze sleeve that has been press fit
into the center of the counterweight will prevent marring of the shaft as you move the counterweights up and down.
Attach Mounting Rings
(purchased separately)
Flat and ribbed plates: constructed with keyhole slots at the location where your mounting rings attach. This feature
enables you to partially loosen the screws on your rings just enough to insert them into the larger part of the keyhole, then
slide the rings to the narrow part and tighten them with a hex key. You can even accomplish this with the rings on the scope,
although this maneuver may be difficult to accomplish with a large, heavy instrument.
We prefer this keyhole method to the standard way of completely removing the screws and possibly dropping them in the
grass.
Astro-Physics or Losmandy Dovetail Plates: Attach the mounting rings to the male dovetail plate (sliding bar).
15

Fine Polar Alignment
For casual observation, you may skip this section and simply start observing. [ Don’t forget to tighten your altitude locking
knobs (2) and pier knobs (4 – Standard Pier Adapter and Hi-Lo Latitude Wedge only) before you begin! ]. Move the telescope
manually or by using the N-S-E-W buttons of the keypad. The keypad and GTO Servo Control Box will function as soon as
they are plugged in. That means that the R.A. axis will be tracking up to the limits of your polar alignment. However, if you
plan to use any of the go-to functions of the 900GTO or do astrophotography, you must perform a more accurate polar
alignment.
Methods for fine polar alignment
•Polar Alignment Scope – Our optional polar scope (PASILL4 or earlier models) will allow you to quickly align your
mount on the pole stars. The reticle was designed for use in both the Northern and Southern hemispheres. Even
users of the GTO computerized mounts will find these polar scopes useful, particularly if your telescope is not
orthogonal to the mount (please refer to the keypad manual for a discussion of orthogonality). If you have a polar
alignment scope, please read the instructions sheets that come with it.
•GTO Keypad – Please refer to the instruction manual for the GTO Servo Drive and read the section describing the
startup sequence. For daytime setup, read the section entitled “Polar Aligning in the Daytime” in the GTO Keypad
manual.
•Star Drift method – Traditionally, this has been regarded as the most accurate method of polar alignment, however
it is also the most time consuming. If you are planning long exposure astrophotos, we suggest that you use the
Polar Alignment Scope (see above), then tweak the final polar alignment by star drifting. Refer to the GTO Keypad
manual for hints on polar aligning using a GTO quick star drift method. The current keypad manual has an
expanded section on this useful alignment method. Also refer to the Technical Support section of our website for
further information. For general information regarding traditional star drift alignment, please refer to the
recommended reading list at the end of this manual and check the internet.
Altitude and Azimuth Adjustments
1. Loosen the altitude - locking knobs (2) and pier knobs (4 – Standard Pier Adapter and Hi-Lo Latitude Wedge only)
and refer back to the section on “Altitude and Azimuth Adjustments – Rough Polar Alignment.” Do not loosen the
Pier Knobs of the Rotating Pier Adapter.
2. Follow one of the methods of polar alignment mentioned above.
3. When polar alignment has been achieved, tighten at these locations (note that the polar axis pivot screws should
have been tight throughout the fine polar alignment process):
Altitude locking knobs (2) – hand tighten
Pier knobs (4 – Standard Pier Adapter and Hi-Lo Latitude Wedge only) – hand tighten
4. For a permanent installation, all knobs in step 3 above may be firmly tightened with the assistance of a hex wrench.
CLUTCH KNOBS AND BALANCING
R.A. and Dec. Clutch Knobs
1. What do they do?
The four R.A. and four Dec. clutch knobs have the function of connecting the R.A. and Dec. axes to their
respective drive worm wheel gears. Their function is progressive, from no tension (axes free to move - as required
during correct balancing of the telescope) to a completely "locked up" state.
2. How can you find out what they really do?
As shipped, all 900 mounts have all four R.A. and Dec. clutch knobs firmly hand tightened. This will give you a
good idea of the maximum tightness (clutch action) that can be achieved by hand effort alone. At this point, you
must bear in mind that for optimum performance all four clutch knobs on each axis (R.A. or Dec.) should be
tightened evenly with the same tension (i.e. all four half tight, all four fully tight, etc.).
In order to feel the effect of the clutch knobs, you may wish to partially assemble your mount. Fit together the R.A.
and Dec. assemblies plus mounting plate and counterweight shaft. Do not put scope and counterweights on at this
stage. With the above assembly (with the clutch knobs firmly hand tightened - "as shipped"), you can feel the
amount of force needed to move each axis by hand. Grab each end of the telescope mounting plate and move it
with a backward and forward movement of the Dec. axis. You will feel considerable resistance to this motion.
Perform the same operation on the R.A. axis by moving the counterweight shaft backward and forward. With a
well-balanced telescope, the above tightness of the clutch knobs will be sufficient for all normal conditions of use.
16

Now, mount up and balance your telescope so you can "feel" what this resistance in R.A. and Dec. (movement
backwards and forwards) is like when you make these motions from the eyepiece end of your telescope as you
would during normal use when slewing (pushing) by hand to acquire an astronomical object within the field of view
of your finder or scope.
3. How tight can the clutch be and can you do any damage by pushing against them?
The maximum tightness of this clutch system is 1/3 turn (with a 5/32 allen key) further in than the tension an
average person can achieve with the knobs by hand. You will see that each clutch knob has a 5/32 hex socket for
tightening with an allen key. With this extra 1/3 turn on each clutch knob, the axis (axes) will be considered
completely "locked up" and you should not attempt to push your scope by hand against this "locked up" resistance,
or undue stress will be placed on the worm wheel/worm and bearings.
However, if you are undertaking a very long astrophoto exposure, it is advisable to increase the pressure on each
clutch knob (with the 5/32 key) by about 1/8th turn on Dec. and 1/8th turn on R.A. You may safely slew the scope
by hand with this tension, however you will notice considerably more effort is required to achieve movement. This is
the absolute maximum tension that can be used for hand slewing. As a general rule, if you have a big scope (7" or
8" refractor) with all the accessories, you will need more clutch tension than a 5" or 6" scope.
WARNING It is also possible to over-tighten the clutch knobs and damage the underlying clutch plugs, so be careful –
these are not lug nuts on your car! (see the troubleshooting section and the appendix for a further discussion of
damaged clutch plugs.)
Balancing Your Telescope
For proper operation, the telescope must be adequately balanced along both axes. Start by balancing the tube assembly.
First, Balance the Declination Axis.
1. Position the mount for balancing. Move the R.A. axis so that the counterweight shaft is pointing down. The
declination axis assembly will be in the meridian (this is the classic photographic pose for a German Equatorial).
Position the Dec. axis so the telescope tube is horizontal and pointing east.
2. Tighten the 4 R.A. axis clutch knobs.
3. Loosen the 4 Dec. axis clutch knobs (about 3/4 to 1 turn) so that the telescope moves freely about the declination
axis. Be careful because if your telescope is significantly out of balance, it may swing rapidly in the out-of-balance
direction!
4. Loosen the tube mounting rings and slide the tube back and forth for balancing. This is best done with the tube in
the horizontal position. If you are using a Losmandy mounting plate, loosen the hand knobs on the female dovetail
plate and slide the Losmandy plate to the desired position.
5. The scope is balanced when it stays put (does not move) with the clutches loose and movement back and forth
about the declination axis has the same feel in both directions. Be mindful of eyepieces, cameras and other
accessories that are yet to be added and compensate accordingly.
Second, Balance the Polar Axis
1. Now, tighten the declination axis clutch knobs and position the mount with the telescope horizontal and the
declination axis horizontal. The counterweight shaft is now horizontal with the center of the counterweights the
same height as the middle of the tube.
2. Loosen the R.A. clutch knobs. Again, be careful because if your scope is significantly un-balanced, it may swing
rapidly in the out-of-balance direction.
3. Move the counterweight(s) up or down to achieve the correct balance in R.A. Again, movement back and forth
about the R.A. axis should have the same feel in both directions.
4. Re-set the tightness of all 8 clutch knobs to the resistance you want making sure that each axis’ 4 clutches are
evenly tightened. (See section on clutch knobs above.)
Try to anticipate any balance problems due to the extra weight of diagonals, heavy eyepieces, finders, solar filters, etc. If the
scope moves by itself, when the clutches are loose, then the scope is not balanced adequately. You may want to “tweak” by
carefully repeating steps 1 – 5 after everything has been attached to the telescope. Be especially careful loosening the Dec.
clutch knobs.
Note: A small amount of imbalance on the East side of the mount is permissible and even desirable for astrophotography and
imaging. This allows gravity to keep the drive train fully engaged while tracking throughout the exposure. If you intentionally
create this small imbalance, you must remember to re-adjust the balance whenever you flip from one side of the mount to the
other. Forgetting to re-adjust can result in a slight see-saw action in tracking that could spoil your next image.
17

SERVO MOTOR DRIVE
GTO Control Box – GTOCP3
The GTO control box contains all of the circuitry to drive the two servo motors and the logic required to navigate the sky. It
will be operational and track at the sidereal rate when connected to both motors of the mount and a power source. In order
to control the movement of the mount, you will need to connect at least one of these:
•GTO Keypad.
•Computer with PulseGuide by Sirius Imaging. The CD for this program is included with the mount. For the most updated
version of the software, check out the website www.pulseguide.com.
•Computer with a planetarium program such as Software Bisque’s TheSky™, Imaginova’s Starry Night™, Nova
Astronomics’ The Earth-Centered Universe (ECU) version 3.1 or later, and Chris Marriot’s Sky Map Pro 6 or any
ASCOM compatible telescope software (all purchased separately).
The GTO Servo Control Box is mounted directly onto the polar axis of the 900GTO mount. Please remember that this box
contains advanced electronics and must be treated with the same care given to other fine equipment. You can see that the
unit is built to be rugged, however it is not indestructible.
Lead-Free (RoHS compliant) Electronics
Starting in 2006, we began phasing in lead-free electronics for all of our mounts. In the first phase, all GTO mounts (and
other electronics) shipped to customers in the European Union were built with lead-free electronic components due to RoHS
regulations that went into effect on July 1, 2006. As of mid 2007, all of our electronics adhere to this safer and more
environmentally responsible standard.
R.A. and Dec. Cable Connections
A “Y” cable with 10-pin connectors is included with your mount. Attach the connector from which the two cables emerge to
the GTO Control Panel. Attach the short part of the “Y” cable to the R.A. motor housing and the long part of the cable to the
Dec motor housing. Lock all connectors. Refer to the section below for further information about positioning the cables.
18

12V Connector
Place the DC power cord (included with your mount) into the DC power plug outlet marked 12V on the GTO Control Panel
and lock in place. Plug the cigarette lighter plug end of the cord into your power source. The acceptable voltage range is 11.5
to 16.Suggested power sources include: portable rechargeable battery pack, auto or marine battery, or power supply (filtered
and regulated) for standard household AC current (110-115 volt – 60 Hz in the US) with a minimum output of 5 amps at 12V
DC. 13 to 16 volts is recommended for best performance. We also recommend that the mount have its own dedicated
power supply and that other devices be powered from a separate source or sources.
There is no on-off switch. We recommend that you plug the power cable into the servo box after the keypad controller. To
turn the unit off, simply disconnect the power cable.
Considerations for observatory installations: We suggest that you disconnect your GTO Control Box from 110V and any
other device (CCD camera, computer, etc) when you are not using your mount so that if your observatory experiences a
power surge or lightening strike, your mount electronics will not be damaged. If you operate your mount remotely, you will
have to leave your power cable connected just as you do for the rest of your electronic equipment. You may want to consider
surge protectors or other protective measures to protect from voltage spikes. A disconnect relay to remove power from both
the 12-volt and ground wire is highly recommended in this situation.
POWER Indicator Light
This LED will remain illuminated when your power source has sufficient output to drive the motors. If the voltage falls below
10.5 volts, the power light will go out and the motors will stop. The keypad controller will not function properly.
For mounts shipped after 02-25-00: If the LED turns yellow, this means that your motors are overloaded, probably due to an
unbalanced load on your mount. Refer to the troubleshooting section of the manual for the solution. Earlier control boxes do
not have this feature.
KEYPAD Connector
Attach the 5-pin male connector of the keypad controller and lock in place (push in the knurled ring then turn).
RS-232 Connectors
These serial port connections are used to connect your mount to your PC computer. You may provide your own straight-
through (non-crossing) cables with a 9-pin (DB9) male connector to interface with the GTO panel, or you can purchase them
directly from us (and be assured that they are the correct type of cable!). We have provided the locking posts to secure the
cable firmly onto the control box. If your serial cable does not have a 9-pin connector, you can use a gender changer or
adapter to convert it. Please note: the use of “crossing,” “reversing,” “null,” or “null modem” cables is a frequent source of
failure and frustration. Make sure that your serial cable is wired straight-through!
When you are controlling the position of the mount with a computer program such as PulseGuide™, Software Bisque’s
TheSky™, or Imaginova’s Starry Night™, the microprocessor chip located in the servo drive box will send continual RA and
Dec. coordinate data via the cable connections to your computer. When you use the software to give instruction to slew to a
new object, the commands (RA and Dec. coordinates) are sent to the mount.
We provide two serial port connections on the mount so that you can use two software programs simultaneously (in addition
to any auto-guider software that may be sending signals to the mount through the Auto-guider Connector). For instance, you
can use PulseGuide for advanced mount control, while using TheSky as a planetarium program. The telescope control
functions of TheSky are more limited so using both in a remote application is advantageous. Since the mount will update the
RA and Dec coordinates simultaneously, both programs are continually updated with the data from the mount. You can
watch the screen display of TheSky to see where your telescope is pointing as it slews. This is most effective if you have a
reasonably fast computer with plenty of RAM. If you try this with a 100MHz processor and only 32 MB of RAM, the response
time will be slow since both programs must be continuously updated with position data.
You must have two serial ports available on your computer to take advantage of this feature. If you use a laptop or a newer
desktop computer, you may need to purchase a USB to Serial Adapter. Starting in the spring of 2008, Astro-Physics will
begin offering single port and four port units made by Keyspan™ that we have found to work quite well on our own
equipment. The serial ports on the GTOCP3 control box will even allow remote operation of your mount, a handy feature
for catching those winter pretties from the warmth of the house. We have tested setups using an Ethernet based USB
Server (also from Keyspan) coupled to the four port Keyspan USB to Serial Converter. The USB Server provided four USB
ports, one of which was used by the four port USB to Serial Adapter, leaving 3 available USB and four available Serial ports
at the mount. The computer was connected to everything via a single RJ45 Ethernet cable. For a more detailed
discussion, go to the Yahoo ap-gto user’s group (access it through our website) and type “pcmcia” “serial” or “usb” into the
search box. Also, be sure to keep an eye on the “What’s New?” pages of the website for further developments in this area.
19