4-12 Troubleshooting
Digital circuit checks
Digital circuit problems can be checked out using Table 4-4.
Table 4-4
Digital circuit checks
Step Item/component Required condition Remarks
1 Power-on test RAM OK, ROM OK. Verify that RAM and
ROM are functional.
2 TP301 Digital common. All signals referenced to
digital common.
3 U103 pin 32 +5V Digital logic supply.
4 U101 pin 48 Low on power-up, then goes
high.
MPU RESET line.
5 U101, lines A1-A18 Check for stuck bits. MPU address bus.
6 U101, lines D0-D15 Check for stuck bits. MPU data bus.
7 U101 pin 44 14.7456MHz MPU clock.
8 U110 pin 13 Pulse train during RS-232 I/O. RS-232 RX line.
9 U110 pin 14 Pulse train during RS-232 I/O. RS-232 TX line.
10 U106 pins 34-42 Pulse train during IEEE-488 I/O. IEEE-488 data bus.
11 U106 pins 26-31 Pulses during IEEE-488 I/O. IEEE-488 command lines.
12 U106 pin 24 Low with remote enabled. IEEE-488 REN line.
13 U106 pin 25 Low during interface clear. IEEE-488 IFC line.
14 U101 pin 84 Pulse train. ADRXB
15 U101 pin 91 Pulse train. ADTX
16 U101 pin 90 Pulse train. ADCLK
17 U101 pin 89 Pulse train. ADTS
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