4-14 Troubleshooting Model 2701 Service Manual
Digital circuitry checks
Digital circuit problems can be checked using Table 4-5.
Analog signal switching states
Table 4-6 through Table 4-12 provide switching states of the various relays, FETs, and ana-
log switches for the basic measurement functions and ranges. These tables can be used to assist
in tracing an analog signal from the input to the A/D multiplexer.
Table 4-5
Digital circuitry checks
Step Item/component Required condition Remarks
1
2
3
4
5
6
7
8
9
10
11
12
Power-on test
J1, pin 3
J1, pin 9
U4, pin 9
J900, pin 1
U1, pin 149
U1, lines A0-A24
U1, lines D0-D31
U1, pin 174
U15, pin 13
U15, pin 14
TP8
RAM OK, ROM OK.
Digital common.
+3.3V (+3.3VD supply)
+4.2V
+4.2V
Low on power-up, then goes high.
Check for stuck bits.
Check for stuck bits.
50MHz
Pulse train during RS-232 I/O.
Pulse train during RS-232 I/O.
500Hz signal.
Verify that RAM and ROM are functional.
All signals referenced to digital common.
MPU supply voltage.
Battery backed memory charge voltage.
Battery voltage (BA-52).
MPU RESET line.
MPU address bus.
MPU data bus.
MPU clock.
RS-232 RX line.
RS-232 TX line.
Signal present if main code is running
properly.
Table 4-6
DCV signal switching
Range Q101 Q102 Q114 Q136 Q109 K101* Q113 Q105 Q104 Q108
Q14/
Q13
100mV
1V
10V
100V
1000V
ON
ON
ON
OFF
OFF
ON
ON
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
ON
OFF
OFF
OFF
OFF
OFF
SET
SET
SET
SET
SET
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
ON
OFF
OFF
OFF
OFF
OFF
ON
ON
OFF
OFF
ON
OFF
OFF
* K101 set states: Pin 8 switched to Pin 7
Pin 3 switched to Pin 4
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