Keithley SourceMeter 3A 2420, Service Manual

Page: 67 / 136

Troubleshooting 4-11
Power supply checks
Power supply problems can be checked out using Table 4-2. See Principles of operation for
circuit theory on the power supply.
Digital circuitry checks
Digital circuit problems can be checked out using Table 4-3. See Principles of operation for
a digital circuit description.
Table 4-2
Power supply checks
Step Item.component Required condition Remarks
1
2
3
4
5
6
7
8
9
Line fuse
Line power
TP502
TP503
TP504
TP505
TP507
TP508
TP510
Check continuity.
Plugged into live receptacle,
power on.
+80V, ±10%
-80V, ±10%
+38V, ±10%
-38V, ±10%
+15V, ±5%
-15V, ±5%
+5V, ±5% Remove to check.
Check for correct power-up
sequence.
Referenced to TP501.
Referenced to TP501.
Referenced to TP501.
Referenced to TP501.
+15VF, referenced to TP500.
-15VF, referenced to TP500.
+5VF, referenced to TP500.
Table 4-3
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
Power-on test
U3 pin 19
U3 pin 7
U3 pin 68
U3, lines A0-A19
U3, lines D0-D15
U3 pin 66
U4 pin 7
U4 pin 8
U13 pins 34-42
U13 pins 26-31
U13 pin 24
U13 pin 25
U3 pin 43
U3 pin 44
U3 pin 45
U3 pin 47
RAM OK, ROM OK.
Digital common. common.
+5V
Low on power-up, then goes high.
Check for stuck bits.
Check for stuck bits.
16.78MHz.
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.
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.
D_ADDATA
D_DATA
D_CLK
D_STB