Digital Circuitry Checks - Keithley 2425 Service Manual

Model 2425 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
1 Power-on test
2 U3 pin 19
3 U3 pin 7
4 U3 pin 68
5 U3, lines A0-A19
6 U3, lines D0-D15
7 U3 pin 66
8 U4 pin 7
9 U4 pin 8
10 U13 pins 34-42
11 U13 pins 26-31
12 U13 pin 24
13 U13 pin 25
14 U3 pin 43
15 U3 pin 44
16 U3 pin 45
17 U3 pin 47
Required condition
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.
Troubleshooting
Remarks
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
4-15