Troubleshooting; Display Board Checks; Power Supply Checks; Table 4-2 Display Board Checks - Keithley 2750 Service Manual

4-14

Troubleshooting

Troubleshooting
Troubleshooting information for the various circuits is summarized below. See
of operation" for circuit theory.

Display board checks

If the front panel DISP test indicates that there is a problem on the display board, use
Table
Table 4-2
Display board checks
Step Item/Component
1 Front panel DISP test
2 P1005, PIN 5
3 P1005, PIN 9
4 U401, PIN 1
5 U401, PIN43
6 U401, PIN 32
7 U401, PIN 33

Power supply checks

Power supply problems can be checked using
Table 4-3
Power supply checks
Step Item/Component
1 Line fuse
2 Line voltage
3 Line power
4 U144, pin 3
5 U101, pin 7
6 U125, pin 3
7 U119, pin 3
8 U124, pin 3
1
TP106
2
TP102
4-2.
Required Condition
Verify that all segments operate.
+5V ±5%
+37V ±5%
Goes low briefly on power up, then
goes high.
4MHz square wave.
Pulse train every 1msec.
Brief pulse train when front panel
key is pressed.
Required Condition
Check continuity.
120V/240V as required.
Plugged into live receptacle,
power on.
+5V ±5%
+37V ±5%
+15.7V ±5%
-15.7V ±5%
+5V ±5%
Model 2750 Multimeter/Switch System Service Manual
Use front panel display test.
Digital +5V supply.
Display +37V supply.
Microcontroller RESET.
Controller 4MHz clock.
Control from main processor.
Key down data sent to main processor.
Table 4-3.
Remove to check.
Check power module position.
Check for correct power-up sequence.
+5VD, referenced to Common D
+37V, referenced to Common D
+15V, referenced to Common A
-15V, referenced to Common A
+5VRL, referenced to Common A
"Principles
Remarks
Remarks
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1
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2
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2
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2
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