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4-10
Troubleshooting
The front panel keys (S901-S931) are organized into a row-column matrix to minimize the
number of microcontroller peripheral lines required to read the keyboard. A key is read by strob-
ing the columns and reading all rows for each strobed column. Key down data is interpreted by
the display microcontroller and sent back to the main microprocessor using proprietary encod-
ing schemes.
Troubleshooting
Troubleshooting information for the various circuits is summarized below.
Display board checks
If the front panel display tests indicate that there is a problem on the display board, use Table
4-1. See Principles of operation for display circuit theory.
Table 4-1
Display board checks
Step Item/component
1
Front panel test
2
J1033
3
U902, pin 1
4
U902, pin 43
5
U902, pin32
6
U902, pine 33
Required condition
Verify that all segments operate.
+5V, ±5%
Goes low briefly on power up, and
then goes high.
4MHz square wave.
Pulse train every 1 ms.
Brief pulse train when front panel key
is pressed.
Remarks
Use front panel display test.
Digital +5V supply.
Microcontroller RESET.
Controller 4MHz clock.
Control from main processor.
Key down data sent to main
processor.
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Table of Contents
Troubleshooting
