4-12 Troubleshooting Model 2500 Service Manual
Digital circuitry checks
Digital circuit problems can be checked out using Table 4-3. See “Principles of operation”
for a digital circuit description.
Table 4-3
Digital circuitry checks
Step Item/component Required condition Remarks
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
Power-on test
U163 pin 19
U163 pin 7
U163 pin 68
U163, A0-A19
U163, D0-D15
U163 pin 66
U166 pin 7
U166 pin 8
U167 pins 34-42
U167 pins 26, 27,
29-32
U167 pin 24
U167 pin 25
U163 pin 43
U171 pin 4
U163 pin 45
U163 pin 47
U165 pin 48
RAM OK, ROM OK.
Digital common.
+5V
Low on power-up, then goes high.
Check for stuck bits.
Check for stuck bits.
20MHz.
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.
Pulse train.
Verify that RAM and ROM are functional.
All signals referenced to digital common.
Digital logic supply.
MPU RESET line.
MPU address bus.
MPU data bus.
MPU clock.
RS-232 TX line.
RS-232 RX line.
IEEE-488 data bus.
IEEE-488 command lines.
IEEE-488 REN line.
IEEE-488 IFC line.
ADRXB
ADTX
AD_CLK
AD_TS
ADSEL
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