Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-15
Troubleshooting
Digital circuitry checks
Digital circuit problems can be checked using Table 4-4.
Tab le 4- 4
Digital circuitry checks
Step Item/Component Required Condition Remarks
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Power-on test
U152, pin 16
U171, pin 16
U194, pin 1
U171, pin 4
U135, pin 68
U135, lines A0-A20
U135, lines D0-D15
U135, pin 60
U159, pin 13
U159, pin 14
U158, pins 34-42
U158, pins 26-31
U158, pin 24
U158, pin 25
U135, pin 48
U135, pin 76
U135, pin 77
U135, pin 74
RAM OK, ROM OK.
Digital common.
+5V (+5VD supply).
+5V (+5VB supply).
+3V
Low on power-up, then goes high.
Check for stuck bits.
Check for stuck bits.
32.758kHz
Pulse train during RS-232 I/O.
Pulse train during RS-232 I/O.
Pulse train during IEEE-488 I/O.
Pulses during IEEE-488 I/O.
Low with remote enabled.
Low during interface clear.
Pulse train.
Pulse train.
Pulse train.
Pulse train.
Verify that RAM and ROM are functional.
All signals referenced to digital common.
Digital logic supply.
Battery backed memory supply.
Battery voltage (BT100).
MPU RESET line.
MPU address bus.
MPU data bus.
MPU clock.
RS-232 RX line.
RS-232 TX line.
IEEE-488 data bus.
IEEE-488 command lines.
IEEE-488 REN line.
IEEE-488 IFC line.
ADRXB
ADTX
ADCLK
ADTS
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