Keithley 2750, Руководство по обслуживанию

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4-14 Troubleshooting Model 2750 Multimeter/Switch System Service Manual
Troubleshooting
Troubleshooting information for the various circuits is summarized below. See “ Principles
of operation ” for circuit theory.
Display board checks
If the front panel DISP test indicates that there is a problem on the display board, use
Table 4-2 .
Power supply checks
Power supply problems can be checked using Table 4-3 .
Table 4-2
Display board checks
Step Item/Component Required Condition Remarks
1
2
3
4
5
6
7
Front panel DISP test
P1005, PIN 5
P1005, PIN 9
U401, PIN 1
U401, PIN43
U401, PIN 32
U401, PIN 33
Verify that all segments operate.
+5V ±5%
+37V ±5%
Goes low briefly on power up, then
goes high.
4MHz square wave.
Pulse train every 1msec.
Brief pulse train when front panel
key is pressed. Use front panel display test.
D5V supply.
D37V supply.
Microcontroller RESET.
Controller 4MHz clock.
Control from main processor.
Key down data sent to main processor.
Table 4-3
Power supply checks
Step Item/Component Required Condition Remarks
1
2
3
4
5
6
7
8
Line fuse
Line voltage
Line power
U144, pin 3
U101, pin 7
U125, pin 3
U119, pin 3
U124, pin 3
Check continuity.
120V/240V as required.
Plugged into live receptacle,
power on.
+5V ±5%
+37V ±5%
+15.7V ±5%
-15.7V ±5%
+5V ±5% Remove to check.
Check power module position.
Check for correct power-up sequence.
+5VD, referenced to Common D
1
.
+37V, referenced to Common D
1
.
+15V, referenced to Common A
2
.
-15V, referenced to Common A
2
.
+5VRL, referenced to Common A
2
.
1
TP106
2
TP102