Keithley 2520, Service Manual, Page: 87 / 137

Model 2520 Pulsed Laser Diode Test System Service Manual Troubleshooting 4-15
Digital circuitry checks
Digital circuit problems can be checked out using Table 4-3 . See “Principles of operation”
on page 4-4 for a digital circuit description.
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
Clip W2
U15 pin 7
U15 pin 68
U15, A0-A18
U15, D0-D15
U15 pin 66
U20 pin 7
U20 pin 8
U5 pins 34-42
U5 pins 26-31
U5 pin 24
U5 pin 25
U15 pin 43
U15 pin 44
U15 pin 45
U15 pin 47 RAM OK, ROM OK.
Digital 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 TX line.
RS-232 RX line.
IEEE-488 data bus.
IEEE-488 command lines.
IEEE-488 REN line.
IEEE-488 IFC line.
D_RETURN_DATA
D_SPI_DATA
D_SPI_CLK
D_SPI_STB