Keithley 2015, Service Manual

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4-18 Troubleshooting
Troubleshooting
Troubleshooting information for the various circuits is summarized below. See Principles 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
4-2.
Table 4-2
Display board checks
Step Item/component Required condition Remarks
1
2
3
4
5
6
7
Front panel DISP test.
P1005, PIN 5
P1005, PIN 9
U401, PIN 1
U401, PIN43
U401, PIN 32
U401, PIN 33
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.
Use front panel display test.
D5V supply.
D37V supply.
Microcontroller RESET.
Controller 4MHz clock.
Control from main processor.
Key down data sent to main
processor.