IMS IMSAI 8080 User manual

IMS ASSOCIATES, INC. USER MANUAL
IMSAI8080
IMSAI

IMSAI 8080 System
General Assembly and
Test Instructions
INTRODUCTION
This chapter contains the following sections:
1. Kit Unpacking Instructions
2. Construction Hints - general notes on how to build your kit.
3. Recommended Overall Order of Assembly (includes cross-reference
to chapters where specific assembly instructions for the various
submodules will be found).
4. Mainframe Assembly - assembly instructions for integrating
Chassis with Power Supply, Mother board and Front Panel, and
instructions for testing the Power Supply.
5. System Functional Test - how to check out your overall system.
17

KIT UNPACKING INSTRUCTIONS
IMSAI 8080 System
General Assembly and.
Test Instructions
1. Remove all packages from the outer box. For a standard
IMSAI 8080 kit, these will consist of:
a. Documentation Set (Manual plus two books)
b. Cabinet Base Plate
c. Table Top Cover (or Rackmount cover and Rackmount
painted pieces)
d. Two large inner boxes
e. Two small inner boxes.
2. Largest inner box contains flat parts such as pc boards,
small sheet metal parts, two plastic panels and a mailing
tube containing the front panel mask and paper backing sheet
(latter is deleted if an OEM machine has been ordered).
3. The next smaller size inner box contains plastic sacks of
components. (There will be a plastic sack with a parts list
corresponding to each pc board, plus sacks for the chassis
and rackmount hardware and a sack containing the paper tape
for the IMSAI Self-Contained System software.
4. One of the two small boxes contains the large components for
the Power Supply (transformer, capacitors, etc.).
5. The second small box is either empty (serving as a spacer box
for packaging purposes) or contains overflow from the sack
parts box.
6. Unpack plastic sacks only when you are ready to begin assembly
of that particular module. If any parts are missing, contact
IMSAI Customer Service for immediate replacement.
7. Be careful in handling the painted sheet metal parts, the
plastic parts and the film negative to avoid scratching.
PC boards should not be stacked without protective material
between to avoid destroying or shorting traces.
18

IMSAI 8080 System
General Assembly Notes
CONSTRUCTION HINTS
GENERAL
The IMSAI 8080 microcomputer is a complex piece of electronic
equipment. This section covers a number of items, each of
which must be followed to insure a working system at the
completion of assembly. This entire section must be read
completely before beginning assembly, and the builder must
refer back to the notes in this section often enough to in
sure that no components are installed incorrectly. While
each assembly step is easy to do correctly, there are many
steps and it is also easy to do one or more incorrectly;
and much more time will be spent solving a problem than would
have been needed to prevent it.
There may be items about which you are not completely sure
during assembly. Should this occur, DO NOT CONTINUE. Study
the manual to see if you can resolve your question, or seek
the help of someone more knowledgeable in digital electronics.
If you feel your question is not resolved by further study or
asking whoever is available to you, call IMSAI. This will
enable you to do a better construction job, and it will enable
us to revise the manual so that it will be of more assistance
to you. We recognize that some builders will have had very
little experience in assembling electronic kits, and it is
our intention to continually revise the manual based on
comments by users, so that even the most inexperienced build
er can achieve the best unit available with a minimum of
effort. No question is too simple to call about if you're
not sure about it.
TOOLS AND WORKPLACE
It is next to impossible for even an experienced builder to
produce a good machine unless proper tools and an adequate
workspace are available. The kit does not require much space
to work in, but enough table surface should be available for
the piece being worked on, all the tools needed for that
piece, and an orderly arrangement of the components which wil.l
be used in assembling that piece. The work area should be
very well-lit, with no shadows. If the entire room is not
well-lit by ceiling or window light, then at least two bright
lamps should be used, preferably one on either side and
slightly behind the chair to help eliminate shadows. You
may want to protect the table surface with cardboard or
newspaper.
19

IMS AI 8080 System
General Assembly Notes
The most important single item in assembly is the solder
ing iron. It is critical enough that a separate part of
this section is devoted to it. Other tools which are ab
solutely necessary to do an adequate assembly job are screw
drivers to fit the screws used in the kit (both straight
slot and phillips), a small pair of diagonal cutters (pre
ferably a 4" pair, flush-cutting), small needle-nosed pliers,
and a wire stripper. A 1/4" nut driver will make cabinet
assembly very much easier, as the sheet-metal screws used
are designed primarily to use a nut-driver. A voltmeter
should be available for testing. Any inexpensive meter (VOM)
with DC voltage scales between 5 and 30 volts should do.
Do not attempt to assemble the kit until you have the tools
necessary; damaged parts cannot be replaced under warranty.
SOLDERING
Almost every problem with an assembled kit is a soldering
problem. If you have never soldered before, or if, you
have done some soldering but do not yet have facility in
making good soldering joints both quickly and every time,
practice before beginning assembly on the IMSAI 8080 boards.
Obtain some extra #20 hook-up wire and solder locally and
solder pieces together until you feel comfortably able to
quickly make a good joint. The importance of good solder
joints is just too great to convey adequately here; but
don't be scared off, because once you get the hang of it,
they're very easy to do.
Soldering Irons
There are a great many tools available with the name "solder
ing iron". Two thirds of these are not appropriate to small
electronics assembly and if used are almost certain to damage
both parts and boards. The problem with most of these are
that they are too big and too hot. Note that most every
soldering "gun" is in the too big, too hot class. Proper
soldering irons are easily available at any local hobbyist
electronics outlet, and they are not expensive. Use a 30-40
watt iron with a small tip, such as an Ungar 776 with a 7155
tip. If you wish to invest in a top-quality tool, a temper- .
ature-controlled tip model such as the Weller W-TCP with a
small 700°F tip is well worth the extra cost. Many irons
are available with either unplated copper tips or plated
tips. Though slightly more expensive, the plated tips
last very much longer and give superior service.

IMSAI 8080 System
General Assembly Notes
Solder
Using the proper solder is as important as using the proper
iron, and there are many solders to choose among. In normal
electronics assembly, separate paste or liquid flux is not
used. Rather, .a solder with a "core” of rosin (or resin)
base flux is Used. This flux (contained in the hollow center
of the solder) should be sufficient. Absolutely avoid any
solders using an acid flux. (Or any cans of acid flux -
unless a can of flux says"rosin" you may safely assume it
is an acid flux. Acid fluxes are used for mechanical sold
ering where the surfaces are not as clean as those in elec
tronic assembly. They are corrosive and will typically
damage a printed circuit.
Also very important is the ratio of tin to lead used in the
solder. Best to use is 63% tin, 37% lead, called 63/37 or
eutectic. Much more common is 60/40, which is still a very
good solder. Avoid using 50/50 or 40/60, even though they’re
a little cheaper. The higher-lead ratios solidify gradually,
while the 63/37 solidifies almost instantaneously, making
"cold solder joints" very much less likely.
Also important is the gauge (or diameter) of the solder.
For fine electronics work a fine gauge should be used,
such as #20 (from #19 to #22 is OK). Again, the correct
solder is easy to obtain from any local hobbyist electronics
outlet or TV repair shop. ERSIN Multicore or KESTER are two
brands you can count on for good results. The solder in
cluded in the kit should be sufficient. If for some reason
it is not, and you cannot obtain the proper solder locally,
DO NOT USE any substitutes. More solder of the proper type
can be detained from IMSAI.
Soldering Technique
For a joint to solder correctly, enough heat must be applied
so that both pieces of metal get hot enough to melt the solder.
The tip of the iron should be applied so .that it touches both
the wire and the foil pad on the board. The end of the
solder should then be touched to the junction of the iron,
lead, and pad, so that a small amount melts and "wets" the
joint (flows smoothly on. both the lead and pad). As soon
as the joint has wet, the iron can be removed, and the joint
inspected immediately. Careful inspection of each joint is
the key to successful soldering. While the solder is being
applied, watch the joint carefully. You should be able to
21

IMSAI 8080 System
General Assembly Notes
see the solder flow onto the two surfaces. It should flow
around the lead, and if you see that the solder has flowed
only on one side of the lead, the iron should be re-applied
(while watching the joint) to heat the joint enough for the
solder to flow. (The typical reason for solder to flow
only half-way around a lead is that not enough heat was
applied.) For the normal joint, only a small amount of
solder is needed (approximately 1/8" of 20 gauge solder
wire) for it to flow all the way around the lead. Also,
for the normal joint, only 2 to 4 seconds of heat applied
from the iron is necessary. More heat and solder will be
needed for some joints with larger leads and holes or large
foil areas, but if more heat or solder is needed on typical
component leads (like IC's), it is an indication that some
thing is not right.
Since nearly all the holes in IMSAI printed circuit boards
are plated-through (the inside walls of the hole have a
metal surface, connecting the pads on the opposite sides
and providing greater area for solder to adhere to) some
solder will typically wick through and be visible on the
top side of the board. This is normal. If small drops
of solder appear on the top side, it is an indication that
too much solder is being applied, along with more than suf
ficient heat. These balls of solder can easily short to
neighboring pins and must be avoided. If the correct amount
of heat or less than the correct amount was used along with
too much solder, the solder remains on the bottom of the
board (the side the solder is always applied from) and
forms a blob which can easily short to neighboring pads or
traces. If one of the small gaps between foil pads or traces
has been shorted with too much solder, it can often be un
shorted by running the hot iron lightly down the shorted
trace, re-melting the solder at the shorted point and pulling
it away with the iron. Do not leave iron on traces or pads
too long when soldering or fixing a short, as overheated
traces easily come off the board. As a result, very special
care must be exercised for any component removal operation.
The tip of the iron must be kept clean to work well. Most
stores that carry irons also carry small sponges in holders
designed for cleaning hot tips. The tip is simply wiped
on the wet sponge quickly. A damp rag will serve as well
though less convenient. The tip must be kept adequately
tinned at all times to avoid an oxide coating forming. It
should appear bright and shiny. A small amount of solder
should be melted onto the tip each time it is cleaned unless
22

IMSAI 8080 System
General Assembly Notes
a joint is to be made immediately. If a tip becomes oxidized,
dipping it in a can of rosin flux is usually sufficient to
enable solder to flow on it again. They may be cleaned of
oxide by fine steel wool or other abrasive, but a plated tip
should never be filed.
The tip of the iron should never have enough solder on it
that it could drip off. If you find that solder tends to
drip off the tip, you are undoubtedly using too much solder.
A solder drip on a P.C. board is often extremely difficult
to see, since it is the same color as the traces, and it is
sure to short several traces and cause trouble or damage
components when the board is operated. Inspect your boards
very carefully for any such solder drips, shorts near soldered
leads, incompletely soldered leads, and unsoldered leads. A
100% inspection of soldering should catch 99% of all problems
before the board is even turned on. When soldering components
with long leads (resistors, etc) we suggest clipping the leads
after soldering so that lead clipping gives you an easy and
positive way to check all the joints on those components. A
completed unit will typically run when first turned on if the
soldering was done correctly.
MOS IC.HANDLING
Some of the chips in the kit are MOS type chips (such as
the 8080A, 8111 and 8251) . MOS chips are sensitive to
static electricity and other large transient voltages. In
order to prevent damaging these, some precautions should
be followed. They all relate to avoiding the discharge of
static through the pins on-one of these chips.
Avoid working in a room with very low humidity. Wearing
cotton fabric or other non-static forming fabrics will
help. Air directly from a heater vent is typically ex
tremely low in humidity and should be avoided in the work
area. Keeping everything involved (chip, board, iron, tools,
boxes, chip containers, work surfaces and you) at.the same
potential is required, and the biggest step in achieving
this is continuous physical contact between them. For example,
before removing a chip from a box and setting it on the table,
the box should be set on the table, you should touch the
table, and only then pick up the chip to place it on the table.
Try to handle the chip from the ends rather than the pins as
23

IMSAI 8080 System
General assembly Notes
much as possible, and always touch the chip's container or
surface which it is touching before picking up the chip.
Also touch a surface or container before placing the chip
back in it. Touch a PC board before inserting the chip.
Touch the soldering iron to the work surface or to a small
piece of metal foil on the work surface before touching it
to the PC board for soldering. In general, make sure the
chip is not the path for any static discharge. Save MOS IC
insertion as the last steps in assembly to avoid unnecessary
exposure.
POLARITY
Many electronic components will not work if they are connected
backwards. Any component which it is important to insert one
way only will have a mark of some sort to indicate which way
is which. The board where they go will have some sort of
corresponding mark at each place, or an indication that all
such components go the same way as a marked "typical" one.
I.C.’s
All I.C.'s must be inserted with pin 1 in the correct location
to avoid damaging the I.C. Pin 1 is indicated on the chips
by several different marks. The most common is a rounded or
square notch in the center of the end near Pin 1. Another
common one is a slightly depressed or raised dot in the
corner of the chip next to Pin 1. One or both of these will
always be present to indicate Pin 1. Sometimes there are
other circular markings on the centerline of the chip, usually
towards one or both ends; these should be ignored. Often there
is some kind of Pin 1 mark on the bottom of the chip also.
(Note: Many I.C.'s have a code for date of manufacture which
is a 4 digit code. e.g. 7425 would indicate manufacture in
the 25th week of 1974. Do not confuse these with the device
number. The code will be alone, the device number will have
manufacturer-dependent suffixes and prefixes, e.g., SN7404N
is a 7404 type chip. On the PC board, some Pin 1 indication
will be found, such as a square pad, a dot, an arrow showing
Pin 1 direction with the note "typical" (indicating all chips
on the board face the same way), or similar mark.
24

IMSAI 8080 System
General Assembly Notes
The board or the chip is v^ry likely to be damaged if there
is a need to unsolder a chip that was soldered in with Pin 1
in the wrong direction. Unless you are completely sure
you are capable of unsoldering an integrated circuit without
damage to the circuit or the board, you should send the
board back to the factory to have the work done for you.
Remember that on these boards with plated-through holes,
pins are not only soldered on the top where you see the
visible bead of solder, but is soldered inside the hole
which makes it much more difficult to remove.
Diodes
Diodes will typically have a band around the body, next to
the cathode end. This corresponds to the bar on the typical
diode symbol. The same is true for Zener diodes. A diode
symbol should be found on the board or assembly diagram to
indicate the proper mounting direction.
Capacitors
Some capacitors have a plus and minus lead; among them the
tantalum and power supply electrolytic capacitors. Some
mark on the body of the capacitor will indicate the plus
lead, typically a + sign near it. There will be a mark
(typically a + sign) on the board or assembly diagram to
indicate the proper direction to mount the capacitors. A
capacitor of this type is usually destroyed very quickly
if power is applied to it in the reverse direction, so check
your assembly carefully.
Transistors
Most transistors have a flat side or a small tab to indicate
the lead orientation. If this indication is oriented accord
ing to the assembly diagram the leads should fit in the holes
with little bending and no crossing.
25

IMSAI 8080 System
General Assembly Notes
MOUNTING COMPONENTS
Integrated Circuit Chips. (IC's)
Some of the chips come in a little plastic rectangle with
an open bottom and top. These can be used as inserters by
setting the carrier with the chips on a piece of felt or
similar material on a table top and pushing lightly with a
pencil eraser or small object that will fit in the top of
the carrier, until the chip has slid down with the leads
resting against the table. Now, because of the material,
the leads will be sticking out beyond the carrier a little
bit* If you then pick up the carrier and the chip and set
it on the board, you can line up the little protruding tips
of the IC’s ends into the holes into which they are supposed
to go, and while you are holding the carrier, push the chip
the rest of the way into the board again with a pencil eraser
or with an object that will fit inside of the carrier.
For the chips that do not come in a carrier, after you insert
the ones that did come in a carrier, you could use those
carriers to insert the others also, by turning the carrier
upside down and setting one of the other chips on the carrier
and pushing it into the carrier and then just continuing the
same process described above, to insert it in its location.
For chips with no such inserter aid available, the pins should
be bent inwards far enough to line up with the holes in the
board. Bend the pins on each side equally. The whole row
of pins on one side can be bent in uniformly if they are all
pressed against a flat surface to bend them. After putting
the chip in the board, two diagonally opposite pins can be

IMSAI 8080 System
General Assembly Notes
bent slightly to hold the I.C. in the board while soldering.
Take special care on each and every chip to observe the
following points:
1. That Pin one is in the correct direction. Refer to
marking on the board or assembly instructions to de
termine which direction pin one belongs.
2. After inserting the chip and before soldering, check
that every pin went through the hole properly. Some
times a pin will catch on edge of a hole and bend under
the chip instead of going through. Care should be taken
to avoid this happening and to check before soldering
to make sure it has not happened.
After inserting one or two chips, get a feel for how much
pressure is needed to push it out of the carrier. Any
chips that seem to take more pressure indicate that perhaps
one or more pins are not lined up with the holes properly.
Most chips after insertion, will stay in the. board securely
due to the fact that the leads are normally bent outward
somewhat and will hold the chip by pushing outward against
the holes. Some chips, however, will be loose after inserted.
Extra care should be taken to see that these are properly
against the board when they are soldered. The board can
either be set flat against the table or other surface that
will hold the chips against the board or two diagonally
opposite ends may be bent slightly to prevent the chip from
dropping out.
Power Regulators
The 7805 regulators for the +5 volts are supplied with a
heat sink and mounting hardware. The three leads must be
bent down at the proper lengths to match the solder pads,
and this should be done with the needle-nose pliers. The
lead should come straight out and bend sharply down, rather
than slope gradually towards the hole. After the leads are
bent, the regulator can be fastened to the board along with
the heat sink, using the short 6-32 screw down from the top,
with the lockwasher and nut on the back. The regulator should
be held to prevent turning while the nut is tightened firmly.
The nut should be tight enough to insure good heat conductivity
between the regulator and heat sink and board. Heat sink
grease may be used if desired.
27

IMSAI 8080 System
General Assembly Notes
Discrete Components
Resistors and diodes can be installed most neatly using a
lead bender to bend the leads consistently. Most pads for
this sort of component are .5" apart.
Disc ceramic capacitors often have the dipped insulation
extending down the leads a short distance, preventing these
from being pulled down all the way to the board. This in
sulation may be broken off by squeezing it in the pliers.
Take it off until the bare wire comes up to the level of
the bottom of the capacitor.
All discrete components should be held in their desired
final position while being soldered. Normally this means
holding them against the board by putting a slight bend
in the lead behind the board so the component cannot lift
from the board. (See the sketch for a way of bending the
leads we find works better than simply finger-bending them
slightly.) Components not held in place look sloppy and
it is much harder to move them once they are soldered. In
some cases, a little extra lead is needed, such as to lay
the disc capacitors down on top of the chips on the front
panel board. In these cases the solution is again to hold
them in their final position during the soldering operation.
This insures that the leads are left the proper length.
28

RECOMMENDED ORDER OF ASSEMBLY
IMSAI 8080 System
General Assembly and
Test Instructions
Step Description Described In
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
MPU Chapter
RAM Chapter
CP-A Chapter
PS-C Chapter
Assemble MPU and RAM boards. Check care
fully.
Assemble CP-A including switches and
flat cable. Check carefully.
Assemble electronic components on Power
Supply. Check carefully.
Assemble Mother board(s). Check carefully Mother Board Chapter
Assemble Chassis sheet metal: Cabinet Assembly
a. Install required number of card guides Chapter
on card frames.
b. Install fan (if supplied) on back frame.
Install line cord through grommet.
c. Bolt together sheet metal parts. Install
rubber feet.
Install Power Supply Board in chassis. Mainframe
Section Assembly
a. Bolt board in place.
b. Bolt transformer in place.
c. Cut wires to length and crimp on (or
solder on) lugs.
d. Connect up Power Supply except for
wires to Mother board(s).
(Connect Mother boards together and) in
stall Mother Board(s) in chassis.
Connect wires to Mother board. Check
carefully.
Prepare front plastic panel assembly.
Plug CP-A board into Mother board.
Connect wires to CP-A board. Install
front panel assembly. Hold CP-A DIP
cable out of way.
Check complete assembly carefully before
applying power. Plug in machine and turn
on. Test Power Supply voltages.
Plug in MPU board and RAM board(s) and
test system.
Assemble other individual boards. Check
carefully.
Install individual boards.
Install required cables. Install Cable
Clamp.
Install Switch escutcheon and cover and/
or Rackmount parts.
Mainframe Assembly
Section
Mainframe Assembly
Section
CP-A Chapter
Mainframe Assembly
General Assembly-
and Test Instruc
tions
General Assembly
and Test Instruc
tions
(Individual board
chapters)
Cabinet Assembly
Section
Cabinet Assembly
Section
29

IMSAI 8080 System
General Assemoiy and
Test Instructions
MAINFRAME ASSEMBLY
Assembly of the mainframe consists of the following steps:
•Power supply installation
•Mother board installation
•Connection between power supply and mother board
•Installation of CP-A panel.
•Connection of power supply and front panel
POWER SUPPLY INSTALLATION
Remove #8 hardware from transformer on Power Supply p.c. board.
Take care to not let the transformer damage the p.c. board. Put
the five #8 screws in the cabinet bottom and secure with the 8-32
threaded spacers. Install the four V - 2 0 nuts and spacers for the
transformer similarly. Carefully lower the Power Supply Assembly
onto the mounting screws so all the screws extend through the board.
Fasten with washers and nuts. See Figure 1. Complete the power
supply by attaching the capacitor brace plate to the bases of the
large capacitors with the adhesive backed foam tape on one side of
the brace plate.
MOTHER BOARD INSTALLATION
Attach the Mother board to the cabinet base with the hardware sup
plied with the Mother board as shown in Figure 2. The front 100-
pin connector should be located in frort of the sheet metal front
frame to accomodate the CP-A assembly.
CONNECTION BETWEEN POWER SUPPLY AND MOTHER BOARD
See the wiring drawing in the Power Supply chapter. Connect the
following wires between the Power Supply and the system:
a) 1 or 2 #18 gauge wire from holes at edge of -16 volt plane
to -16 volt trace on Mother board.
b) 1 or 2 #18 gauge wire from holes at edge of +16 volt plane
to +16 volt trace on Mother board.
c) 2 or 3 #14 or #12 gauge wire from +8 volt plane to +8 volt
bus on Mother board.
30

TRANSFORMER
FOOT
r - V," - 20 x 1!
/ r K" -:
5U22J
KTOW1
vnnn
V." - 20 x 114" BOLT
20 NUT
14" SPLIT LOCK WASHER
x 1/16 FLAT WASHER
ID X 1/16" + THICK
NYLON WASHER
- - THREADED SPACER . NYLON
' '/." - 20 x .500" HIGH
HEX OR ROUND
UlTirmti m u± z m m in n n nn-rrrm
8 - 32 x IX" MACHINE SCREW
8 - 32 NUT
No. 8 STAR LOCKWASHER
No. 8 x 1/16" NYLON WASHER
eaasr
PSC BOARD
THREADED SPACER - NYLON
No. 8 -32 x .500" HIGH
HEX OR ROUND
I B / / / / / / / / / z ' / / / > . ‘ - x - BASEPLATE
4 PLACES 5 PLACES
PS-C BOARD MOUNTING SYSTEMS
MAINFRAME ASSEMBLY
FIGURE 1
> 0 =
zrnÄ
jjj>S
-lfnJ<
2 3 3

I MSA I 8080 SYSTEM
GENERAL ASSEMBLY
AND TEST INSTRUCTIONS
MOTHERBOARD MOUNTING SYSTEM
6—3 2 x * " NYLON SCREW
4 PER E X P -4
8 PER E X P -6
24 PER E X P -2 2
MAINFRAME ASSEMBLY
FIGURE 2
o

d) 2 or 3 #14 or #12 gauge wir ® from ground plane to ground
bus on Mother board.
e) 2 #18 gauge wires from External Switch pads to power switch
on CP-A or on back panel.
f) 2 wires (#18 or #20 gauge) from switched AC pads to fan (if
fan installed) install insulated tubing over fan terminals.
g) 3 wires from power cord to terminals W, G, and B on PS-C.
Make sure the power cord wire colors match the label on
the panel
INSTALLATION OF CP-A PANEL AND CONNECTION TO POWER SUPPLY
Plug the completed CP-A panel into the front 100 pin connector on
the Mother board. Install the eight Allen head screws into the
PEM nuts on the sheet metal front frame. Solder the two #18 gauge
wires from the External Switch pads on the Power Supply assembly to
the power switch pads on the CP-A panel. Provide as much clearance
as possible between the connections on the CP-A board and the sheet
metal front frame. Be careful not to damage the acrylic panels
with the soldering iron.
CHECK OUT OF POWER SUPPLY
Before plugging in circuit boards except the CP-A board,
the unit should be plugged into the AC power supply and
the power supply turned on by depressing the front panel
rocker switch. The voltages at the outputs should then
be measured (any DC volt meter with a full scale voltage
of 20 to 50 volts will do) and the voltages should read
approximately 18 volts on the +18 and -18 volt outputs,
and 10 volts on the +8 volt output. If the voltage does
not come to these values, a check should be made that
the positive and negative terminals of the capacitors are
connected properly and the diodes are mounted properly.
If there is a problem with any of these items a wiring
error has probably been made and the wiring should be re
checked carefully. If the wiring is checked and no error
is found, assistance should be sought from a person know
ledgeable in electronics or from the factory.
When the voltage of the capacitors has been checked out
to be satisfactory, the unit may be turned off. A 10
minute wait will permit the capacitors to discharge.
While there is considerable energy stored in the power
supply filter capacitors when they are fully charged, the
voltage levels are not high enough to present a danger.
Some care should be taken, however, not to discharge the
capacitors by shorting them with a tool or other metallic
object.
IMSAI 8080 System
General Assembly and
Test Instructions
33

IMSAI 8080 System
General Assembly and
Test Instructions
With the Power Supply checked out and operating
properly, the rest of the system is ready to
be tested. The MPU board should be inserted in the
slot behind the front panel with the flat cable
inserted into the socket in the upper right hand
corner of the MPU board before the board is fully
seated.
The memory board should then be inserted in the
third slot. While it is not necessary that the
first memory board be addressed beginning at po
sition 0, it is normally expected and the rest of
this section will assume that the memory board
jumpers were wired according to the directions
in the User Guide section of the RAM-4A board for
addressing the board at 0.
The slots in the Mother board are not unique and
if a larger version (e.g., 22 slot) was ordered
with more edge connectors, the boards need not be
plugged into the second and third slot as directed
but may be plugged into any slots.
SYSTEM FUNCTIONAL TEST
When the boards are installed, the machine is
ready to test. Turn the power on with the front
panel rocker switch and depress the RUN/STOP
switch momentarily to STOP position and release.
The WAIT light should be on and the RUN and HOLD
lights should be off, with the other lights in
various states at this time. Raise the RESET
switch momentarily to the RESET position and
release. AIL the lights on the bottom row in
the ADDRESS BUS section should be indica
ting that the program counter is set to loca
tion 0. The WAIT light should still be on with
the RUN and HOLD lights off. The DATA BUS lights
may show various random bits on and the STATUS
byte should have three lights on: MEMR, Ml,
and WO. With all 16 ADDRESS switches in the down
or 0 position, the EXAMINE/EXAMINE NEXT switch

IMSAI 8080
General Assembly and
Test Instructions
should be raised momentarily to the EXAMINE position and
released. Check that the lights after this operation are
exactly the same as described for after the RESET switch
was operated.
The machine is now ready to enter a small test program. For
complete description of program
An Introduction To Microputers.
the following program should be
TEST PROGRAM
ADDRESS
1
HEX BINARY
0DB 1101 1011
1FF 1111 1111
2D3 1101 0011
3 FF 1111 1111
4 C3 1100 0011
5 00 0000 0000
6 00 0000 0000
TEST PROGRAM
ADDRESS
2
HEX BINARY
0 DB 1101 1011
1FF 1111 1111
2 2F 0010 m i
3D3 1101 0011
4FF 1111 m i
5C3 1100 0011
600 0000 0000
700 0000 0000
operation in computers, read
For the initial machine test,
entered:
OCTAL
333 INPUT
377 ADDRESS
323 OUTPUT
377 ADDRESS
303 JUMP
000 LOW ADDRESS
000 HIGH ADDRESS
OCTAL
333 INPUT
377 ADDRESS
057 COMPLEMENT DATA
323 OUTPUT
377 ADDRESS
303 JUMP
000 LOW ADDRESS
000 HIGH ADDRESS
35