Troubleshooting
Troubleshooting information for the various circuits is summarized below. See Analog signal
switching states for additional information regarding the analog circuitry.
Display board checks
If the front panel DISP test indicates that there is a problem on the display board, use
Table 4-2. See Principles of operation for display circuit theory.
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, pin 43
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 1ms.
Brief pulse train when front panel key
is pressed.
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.
4-10 Troubleshooting
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