HP 85662A Operating instructions

Troubleshooting and Repair Manual
HP 85662A Spectrum Analyzer IF-Display Section
HEWLETT
PACKARD
HP Part No. 85662-90085
Microfiche Part No. 85662-90086
Printed in USA December 1990

@Copyright Hewlett-Packard Company 1990
All Rights Reserved. Reproduction, adaptation, or translation without prior written
permission is prohibited, except as allowed under the copyright laws.
1212 Valley House Drive, Rohnert Park, CA 94928-4999, USA

Certification
Hewlett-Packard Company certifies that this product met its published specifications at the
time of shipment from the factory. Hewlett-Packard further certifies that its calibration
measurements are traceable to the United States National Institute of Standards and
Technology, to the extent allowed by the Institute’s calibration facility, and to the calibration
facilities of other International Standards Organization members.
Warranty
This Hewlett-Packard instrument product is warranted against defects in material and
workmanship for a period of one year from date of shipment. During the warranty period,
Hewlett-Packard Company will, at its option, either repair or replace products which prove to
be defective.
For warranty service or repair, this product must be returned to a service facility designated
by HP. Buyer shall prepay shipping charges to HP and HP shall pay shipping charges to
return the product to Buyer. However, Buyer shall pay all shipping charges, duties, and taxes
for products returned to HP from another country.
HP warrants that its software and firmware designated by HP for use with an instrument
will execute its programming instructions when properly installed on that instrument. HP
does not warrant that the operation of the instrument, or software, or firmware will be
uninterrupted or error-free.
Limitation of Warranty
The foregoing warranty shall not apply to defects resulting from improper or inadequate
maintenance by Buyer, Buyer-supplied software or interfacing, unauthorized modification or
misuse, operation outside of the environmental specifications for the product, or improper
site preparation or maintenance.
NO OTHER WARRANTY IS EXPRESSED OR IMPLIED. HP SPECIFICALLY
DISCLAIMS THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE.
Exclusive Remedies
THE REMEDIES PROVIDED HEREIN ARE BUYER’S SOLE AND EXCLUSIVE
REMEDIES. HP SHALL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL,
INCIDENTAL, OR CONSEQUENTIAL DAMAGES, WHETHER BASED ON
CONTRACT, TORT, OR ANY OTHER LEGAL THEORY.
Assistance
Product maintenance agreements and other customer assistance agreements are available for
Hewlett-Packard products.
For any assistance, contact your nearest Hewlett-Packard
Sales and Service Ofice.
. . .
III

Safety Symbols
The following safety symbols are used throughout this manual. Familiarize yourself with each
of the symbols and its meaning before operating this instrument.
Caution
I)
The caution sign denotes a hazard. It calls attention to a procedure which,
if not correctly performed or adhered to, could result in damage to or
destruction of the instrument. Do not proceed beyond a caution sign until the
indicated conditions are fully understood and met.
Warning
The warning sign denotes a hazard. It calls attention to a procedure which,
if not correctly performed or adhered to, could result in injury or loss of life.
Do not proceed beyond a warning sign until the indicated conditions are fully
understood and met.
General Safety Considerations
Warning
9
Before this instrument is switched on, make sure it has been properly grounded
through the protective conductor of the ac power cable to a socket outlet
provided with protective earth contact.
Any interruption of the protective (grounding) conductor, inside or outside
the instrument, or disconnection of the protective earth terminal can result in
personal injury.
Warning
There are many points in the instrument which can, if contacted, cause personal
9
injury. Be extremely careful.
Any adjustments or service procedures that require operation of the instrument
with protective covers removed should be performed only by trained service
personnel.
Caution
Before this instrument is switched on, make sure its primary power circuitry
has been adapted to the voltage of the ac power source.
Failure to set the ac power input to the correct voltage could cause damage to
the instrument when the ac power cable is plugged in.

Contents
IF-Display Section
General Information
IF Overall Block
Diagram
Al Display Section
A3 Digital Storage
Troubleshooting
A4 IF Section
Troubleshooting
Options
General Parts Listing
Major Assembly and
Component Locations
General information on the contents of the manual, including storage,
shipment, and packaging.
Mnemonic Table, Instrument Bus Pin Connection Table, and Overall
IF Block Diagram.
Al Display Section Troubleshooting information, Block Diagram, and
AlAl through AlAlO service sheets.
A3 Digital Storage Troubleshooting information, Block Diagram, and
A3Al through A3AlO service sheets.
A4 Section Block Diagram, and A4Al through A4AlO service sheets.
Information and service sheets that explain the difference between an
IF-Display Section with an option and a standard IF-Display Section.
Replaceable parts information and parts identification figures.
Major assembly and component locations.
Contents 1

IF-Display Section General Information
IF-Display Section Service
Introduction
This Troubleshooting and Repair Manual contains information for the troubleshooting and
repair of the IF-Display Section of the instrument. This information is combined in service
sheets and indexed with tabs for quick reference.
Instruments Covered by This Manual
n HP 85662A IF-Display Sections, serial number prefixes 2403A and above.
n Option 067 (1 kHz to 3 MHz Resolution Bandwidths for the HP 8567A Spectrum Analyzer),
w Option 400 (400 Hz operation)
n Option 462 (Impulse Bandwidths)
n Option H96 (30 Hz-l MHz Resolution Bandwidths)
HP 85662A IF-Display Sections with serial number prefixes below 24038 are covered in both
Volume 3 of the HP 8566A Operating and Service Manual (HP part number 08566-90006) and
Volume 3 of the HP 85688 Operating and Service Manual (HP part number 08568-90012).
How the HP 85662A Is Used
n HP 85662A IF-Display Section is used with:
q HP 85660B RF Section as the HP 8566B Spectrum Analyzer
q HP 85680B RF Section as the HP 8568B Spectrum Analyzer.
w Option 462 is used with:
q HP 85660B RF Section as the HP 8566B Option 462 Spectrum Analyzer
q HP 85680B RF Section as the HP 8568B Option 462 Spectrum Analyzer
n Option 067 is used with:
q HP 856708 RF Section as the HP 85678 Spectrum Analyzer
n Option H96 is used with:
•I HP 85680B Option H96 as the HP 8568B Option E96 Spectrum Analyzer
o HP 85680B Option H44 as the HP 8568B Option E44 Spectrum Analyzer.
IF-Display Section General Information 1

Service Sheets
The service sheets in this manual are organized in alpha-numeric order and are indexed with
tabs to make it easy to locate a specific service sheet. Each of the service sheets contain the
following information:
n Circuit Description (where practical)
n Troubleshooting Hints (where practical)
n Replaceable Parts Lists
n Block Diagram (where practical)
n Component Location Illustrations
n Schematic Diagrams
Repair Procedures
Repair procedures are included for use in removing and replacing assemblies for repair. They
are located in the following sections:
n Front-Panel LED Replacement
Tab: AlAl Keyboard
u Front Panel Removal and Repair
Tab: AlAl Keyboard
n CRT Replacement
Tab: AlA High Voltage Regulator
n IF-Display Section Internal Fuse Replacement
Tab: AlA f15 V Regulator and High Voltage
Major Assembly and Component Locations
Major assembly and component location illustrations for the IF-Section are located at the rear
of this manual.
Troubleshooting
Troubleshooting information for the IF-Section is divided into two levels as follows:
n Section Level
IF Overall Block Diagrarn
Al Display Section Block Diagram
A3 Digital Storage Troubleshooting
A4 IF-Section Troubleshooting
n Assembly Level
Most assemblies have troubleshooting hints immediately following their circuit
descriptions. Troubleshooting information is also located on assembly-level block
diagrams, notes, and schematics.
2 If-Display Section General Information

All assemblies are indexed by tab except for the ones listed in Table 1 at the end of this
section. Table 1 lists the index tabs where these assemblies can be found.
Assembly Locations
I
Assembly 1
Tab Location
I
AlA Rectifier, Block Diagram
General Parts Listing, Table 6
AlVl
AlAll
A2
AlA High Voltage Regulator, Block Diagram
General Parts Listing, Table 6
AlA High Voltage Regulator, Block Diagram
General Parts Listing, Table 4
Not Assigned
Storage and Shipment
Environment
The instrument may be stored or shipped in environments within the following limits:
Temperature
...................................................
Humidity
..-40’Ct o +75OC
...............................................
..5%t to 90% at 0”to 40°C
Altitude
.........................................
.Up to 15,240 meters (50,000 feet)
The instrument should be protected from temperature extremes which might cause
condensation within the instrument.
Original Packaging
It is recommended that the original factory packaging materials be retained for use when
shipping the instrument. If original packaging material cannot be retained, packaging
materials identical to those used in factory packaging are available through Hewlett-Packard
offices. Part numbers and descriptions of the packaging materials are listed in Figure 1.
The combined weight of the two instrument sections is approximately 50 kg (112 lbs).
Because of the weight involved, do not package the instrument sections fastened together as
one unit. The instrument sections must be separated and packaged in separate containers.
The quantity of packaging materials in Figure 1 is for only one instrument section.
If the instrument is being returned to Hewlett-Packard for servicing, attach a tag to each
carton indicating the type of service required, return address, model number, and full serial
number. For your convenience, a supply of tags is included at the end of this section. Also,
mark each container FRAGILE to assure careful handling. In any correspondence, refer to the
instrument by model number and full serial number.
Other Packaging
If it is necessary to use packaging materials other than the type used in original factory
packaging, the following general instructions should be followed.
IF-Display Section General Information 3

1. Separate the two instrument sections and wrap each in heavy paper or plastic.
2. Place the instrument sections in separate containers with 8 to 10 cm (3 to 4 inches) of
shock-absorbing material around all sides to provide firm cushioning and prevent movement
inside the container. Protect front panels with cardboard. Double-wall corrugated cartons
of 125 kg (275 lb) bursting strength are sufficient for shipping containers.
3. Seal each container securely and, if shipping to a Hewlett-Packard office or service center,
attach a tag to each container indicating the type of service required, return address, model
number, and full serial number. For your convenience, a supply of tags is included at the
end of this section.
4. Mark each container FRAGILE to assure careful handling.
I TEM
QTY
0 1
1
0 2
2
0 3
1
HP PART NO.
921 l-4487
5180-2319
5 180-2320
DESCRIPTION
OUTER BOX
INNER FOAM PAD
INNER BOX
Figure 1. Packaging for Shipment Using Factory Packaging Materials
4 IF-Display Section General Information

IF Overall Block Diagram
Table 1. A3 Digital Storage Mnemonic Table
Mnemonic Description Mnemonic Description
184MHZ LO 18.4
MHz Local Oscillator Signal
LDRMP
Load Ramp Register
[MHZ
1 MHz ADC Clock
LDSR
LOW = Digital Storage Ready
21.4MHZ
21.4 MHz IF Signal
LDX
Load X Position Register
3 MHZ 3
MHz IF Signal
LDY
Load Y Position Register
A LOG Log Expand Control
LFSEN
LOW = Fast Sweep Enable
A0 - All
Accumulator Bus Bits 0 through 11
LG 10 Linear
Gain Controls
AlOdB Attenuation Controls LG20
A20dB LGCLK
200 kHz Line Generator Clock
A2dB LGX
Line Generator Horizontal Signal
A4dB
LGY
Line Generator Vertical Signal
AMB LINCRSA
Increment Stroke Address
ADRO Instrument Bus Address Bits 0 through 3 LINTG
LOW = Integrator Control
ADR3 LL Long
Line
AUX BLANK Auxiliary Blanking Output
LLGBLANK
LOW = Line Generator Blanking Control
4ux z Auxiliary Z Axis Output LLL LOW = Long Line
4VdB Attenuation
Control LMEMEN
LOW = Enable Memory Output
2 LOG Log Expand Control Log/Linear Control
BCI - Bll
Digital Storage Bus Data Bits 0 through 11 LQ LOW = Selected Qualifier
BLO - BL6
Branch Length Bus Bits 0 through 6 LROMEN
LOW = ROM Enable
BLINK Blink CRT Display Control
LRSTO
LOW = Reset Trigger Occurred
BRIGHT
Bright CRT Display Control LRTN
LOW = Enable Interrupt Return
BS Block Switch Control LRTRC LOW = Retrace Signal
BWS Bandwidth
Controls
LTlo
LOW= IF-Display Section l/O Strobe
BW63 LTON
LOW = Turn On
BW68
LTSTA
LOW = Input Test A Data
BW7
LTSTB
LOW = Input Test B Data
CE
Memory Chip Enable LWRITE Memory Write Control
ZHAR
Character Mode Display Control LZERO Output of Zero Check on ALU Result
>LK 8 MHz System Clock MAO-MA11
Memory Address Bus Bits 0 through 11
IF Overall Block Diagram

Table 1. A3 Digital Storage Mnemonic Table (continued)
Mnemonic
CRT DSBL
AX
AY
DIM
DOTEN
Fo - F11
FCO - FC3
PSO - PS3
FREQ ZERC
FS
FSOUT
FSZ
HLDX
HLDY
HOLD
HSWP
[CLK
INSELA
INSELB
MTG
INTR
[OBO
[OB15
[OC
KS0 - KS3
LO-L7
;ADC
;BLANK
.CLK
LCLRSA
LDCHAR
LDEXP
LDM EN
;DMAR
;DMDR
Description
CRT Disable Control
Delta X Position
Delta Y Position
Dim CRT Display Control
Dot Enable
Function Bus Bits 0 through 11
Data Manipulator Function Control Bits C
thru3
l/O Port Selection Bits 0 through 3
Frequency Zero Control
Fast Sweep Mode
Fast Sweep Output
Fast Sweep Z Axis
Hold X Position (Sample and Hold Control
Hold Y Position (Sample and Hold Control
Track and Hold Control
HGH = Sweeping
ndicator Clock (Front-Panel LEDs)
Input Selection Bit A
tnput Selection Bit B
[ntegrator Control
[nterrupt
[nst-ent Bus Data Bits 0 through 15
l/O Port Input/Output Control
>onstant Selection Bits 0 through 3
Jnk State Bus Bits 0 through 7
.OW = Enable ADC Output
.OW= Blanking Control
nverted CLK
LOW = Clear Stroke Address
Load Character Register
Load Expand Register
lata Manipulator Output Enable
doad Memory Address Register
dad Memory Data Register
Mnemonic
NSO - NS7
OS10
0520-l
3320-2
PENLIFT
?OS
QSO - QS3
RO-R11
RBWA
XBWB
?tBWC
XBWD
XEC CAL
IEC ZERO
tMo - RM2
RSEN
RSHS
50 - Sll
so -s7
jGl0
jG20-1
;G20-2
iMPL
iTROK8
iWITCH
IBWA
rBWB
V’BWC
irBWD
0DEO
c
c
:
Description
Next State Bus Bits 0 through 7
Offset Gain Controls
iecorder PENLIFT Control
sign of ALU Results
Qualifier Selection Bits 0 through 3
Ram Bus Bits 0 through 11
!tesolution Bandwidth Controls
Recorder Calibrate
tecorder Zero
ti Register Select Bits 0 through 2
Reset Peak Detectors Enable
beset High Sweep
source Bus Bits 0 through 11
state Bus Bits 0 through 7
step Gain Controls
iample
itroke 8 of Current Character
Jp/Down Converter Control
ride0 Bandwidth Controls
Jideo Signal
Iorizontal Signal to CRT
Vertical Signal to CRT
ntensity Signal to CRT
2 IF Overall Block Diagram

Table 2. BO-Wire Instrument Bus Pin Connection Table for IF-Display Section
pin
Signal
1
GND
2 NC
3IOBO
4 IOB I
5 IOB2
6 IOB3
7 IOB4
8
IOB5
9
IOB6
10
IOB7
11
IOB8
12 IOB9
13 IOBlO
14 IOBll
15
IOB12
16 IOB13
17 IOB14
18
IOB15
19 NC
20 NC
21 NC
22 HPON
23 ADRO
24 ADRl
25
ADRP
Description
Ground
No Connection
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
Instrument Bus
Data Bits 0 -
15
No Connection
No Connection
No Connection
HIGH = IF-Display Section
Power ON
Instrument Bus
Address Bits 0
-4
Instrument Bus
Address Bits 0
-
4
Instrument Bus
Address Bits 0
-
4
Pin Signal
Description
26 ADR3
Instrument Bus Address
Bits 0 - 4
27 ADR4
Instrument Bus Address
Bits 0 - 4
28 ADRS Address Bit 5 not used
29 NC
No Connection
30 NC
No Connection
31 KR8 Key Rows 8
- 11
32 KR9 Key Rows 8
- 11
33 KRlO Key Rows 8
- 11
34 KR 11 Key Rows 8
- 11
35 KC0
Key Columns 0 - 7
36 KC1
Key Columns 0 - 7
37 KC2 Key Columns 0
- 7
39 KC4 Key Columns 0
- 7
40 KCS
Key Columns 0 - 7
41 KC6
Key Columns 0 - 7
42 KC7 Key Columns 0
- 7
43 LSTP LOW = Stop Processor
44 HSWP HIGH = Sweeping
45 LSRQ LOW = Service Request
46
LDSR LOW = Digital Storage Ready
47 LB10
LOW = RF Section I/O Strobe
48 GND
Ground
49 LTlO LOW = IF-Display Section I/O
Strobe
50 GND Ground
IF Overall Block Diagram 3

Al
Display Troubleshooting
The Display system consists of four sections:
Input Section A3A8 Analog-Digital Converter and A3A9 Track and Hold
Processor Section
A3A4 Memory, A3A5 Data Manipulator, A3A6 Main Control,
and A3A7 Interface
CRT Driver Section A3Al Trigger, A3A2 Intensity Control, and A3A3 Line
Generator.
CRT Amplifier Section
AlA High Voltage Regulator and either AlA XYZ Driver
Amplifier (Serial Prefixes 3004A and above) or AlA Z Axis
Amplifier AlA X Deflection Amplifier and AlA Y Deflection
Amplifier
Isolation of a malfunction to one of the above sections is done with the use of rear-panel
display outputs and the internal test programs.
If the left INSTR CHECK LED is on, a failure has probably occurred in Digital Storage.
Refer to the A3 Digital Storage Troubleshooting notes for the correct troubleshooting
procedure.
The following paragraphs briefly describe the failure modes and appropriate places to begin
the troubleshooting.
Characters Only
If only the characters on the CRT display are affected, the problem most likely exists on the
A3A4 Memory.
Graticule and Characters Only
If the graticule and characters are incorrect, but the video information appears to be correct,
suspect the System ROMs on A3A6 first. Also the “long POP” test of the RF Section
memory should be performed. Refer to the Digital Storage Troubleshooting notes for more
information.
Al 1

Video (Signal) Only
If only the video information is incorrect, suspect A4 IF Section, A3A8, or A3A9. To
eliminate the IF, connect the rear-panel SWEEP and VIDEO RECORDER OUTPUTS to an
oscilloscope. If the video is correct, then either A3A8 or A3A9 is defective.
Remove cable 96 from A3A9Jl. Then jumper A3A8TPl to A3A9TP3 and push Instrument
Preset. This substitutes the sweep ramp for the video input. The CRT display is similar
to Figure 7 in the A3A8 tab. If the ramp is incorrect, remove A3A9, jumper A3A8TPl to
A3A8TP6 and push Instrument Preset. The CRT display is the same as Figure 7 in the
A3A8 tab. If the display is correct, the problem is in the A3A9 assembly. Refer to A3A9
Troubleshooting procedure. If ramp is incorrect, suspect ADC on A3A8. See the A3A8
Troubleshooting notes to verify this.
Don’t rule out the sweep system, especially the ramp converter on A3A8, when
troubleshooting video failures. Some ramp converter failures produce CRT displays that are
similar to those caused by ADC failures.
All CRT Information Blank or Distorted
Check X, Y, and Z DISPLAY OUTPUTS on rear panel. If these are correct, the fault is most
likely with the X/Y Deflection Amplifiers or Z Axis Amplifier (or AlA XYZ Deflection
Amplifier). The following program, which places a dot at the center of the display, is helpful
when troubleshooting the Deflection Amplifiers. It balances the voltages in both halves of the
circuitry. Press Instrument Preset and key in the following:
Blank Trace A, (%K), Recorder Lower Left, 0 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . .DSPL ADRS
[e), Recorder Upper Right . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .WRITE
1090 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vector Command
512 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..X coordinatesforcenter screen
512 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Y coordinates for center screen
1092 Hz . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
End of display
If the X, Y, and Z DISPLAY OUTPUTS produce either distorted or no output, Digital
Storage must be tested. Connect a jumper from A3A6TP3 to A3A6TP6 and push A3A7Sl.
The Digital Storage Test Pattern (Figure 1 of the A3 Digital Storage Troubleshooting tab)
results. Refer to the Digital Storage Troubleshooting procedures. If the test pattern is correct,
start with the system ROMs check.
If the test pattern is incorrect, verify operation of A3A3 Line Generator and A3A2 Intensity
Control. Refer to the troubleshooting information included with the schematics. If A3A3 and
A3A2 are working properly, then all of Digital Storage will have to be checked, starting with
A3A6.
Whenever the display is blank, and the left INSTR CHECK LED is off, check the AlA
f15 V Regulator (or AlA High Voltage Power Supply) and AlA +lOO V, t5.2 V
Regulator. The power supply LEDs indicate the presence of voltage but not regulation. Verify
operation of A3A2 Intensity Control and AlA Z Axis Amplifier. If these are all working
properly, carefully examine the AlA High Voltage Regulator assembly.
If the CRT is blank, check the CRT oscillator to see if it is turned off. Measure AlA6TP6
with a DVM. If TP6 is a digital high, the CRT will not operate since the oscillator is turned
off. Troubleshoot AlA to check for bad components, shorts, and so forth. If the AlA is
operating correctly, check the CRT disable line from A4A9U14. If the IC is damaged, it
2 Al

can cause the CRT to be disabled. If U14 is operating correctly, visually inspect the A4A9
assembly.
Al 3

AIAI
AlAl Keyboard, Circuit Description
AlAl Keyboard consists of three functional blocks: CRT Controls, Keyboard Switches, and
Status Indicators.
CRT Controls (A)
The CRT Controls include the following front-panel potentiometers:
n INTENSITY control Rl. Sets the level of the input to AlA 2 Axis Amplifier.
n ALIGN screwdriver adjustment R8. Sets the CRT trace to horizontal.
n FOCUS screwdriver adjustment R2. Focuses the CRT trace.
n FREQ ZERO screwdriver adjustment R3. For resolution bandwidths of 1 kHz or less,
adjusts the frequency of the 18.4 MHz oscillator (A4A5 Step Gain) to precisely align the IF
passband to 21.400 MHz.
The front-panel STANDBY indicator, LED DS16, which is driven by the PWR DWN signal
from AlA f15 V Regulator, is activated when line power is applied while the power supply
regulators are off.
Keyboard Switches (B)
The Keyboard Switches are a matrix of rows and columns connected to the RF Section
keyboard by the 50-wire Instrument Bus W8. When a keyboard switch is activated, Al5
Controller recognizes the switch and performs the indicated operation.
Status Indicators (C)
The 17 Status Indicators, LEDs DSl through DS15, DS17, and DS18, show the states of the
various keyboard functions. Al5 Controller loads the latches Ul and U2 via the Instrument
Bus W8. The latch address is decoded in A3Al Trigger, which generates the ICLK strobe
signal.
Front-Panel LED Replacement
1. Set instrument LINE switch to STANDBY.
2. Loosen set screws in INTENSITY control and Video Trigger LEVEL control knobs @ and
0 and remove knobs. See Figure 1.
AlAl 1

FRONT PANEL VIEW
1
9
\
p
bel 0 on 06
..
.
cjii Ii 00 ofi
.
q ocjb oocl
00 0 0000
2
/o
Figure 1. Front Panel Control Knobs
3. Remove nut from INTENSITY control and from Video Trigger LEVEL control using a
5/16-inch wrench.
4. The dress panel is now loose. It may be necessary to pry front panel out slightly using a
sharp instrument such as a knife blade along the edge of the panel.
5. Remove the Front Panel by removing the 8 screws @ around its edge. The LEDs are now
accessible for replacement. Unsolder the leads of the LED from the rear of the printed
circuit board. Pull out the LED and its standoff. Insert a new LED in the standoff and
replace it on the board with the negative lead (cathode) to the square pad on the printed
circuit board. Refer to Figure 2 for identification of LED leads. Solder leads to printed
circuit board and trim excess lead length and reassemble the front panel.
2 AlAl