Keithley 2520, Service Manual, Page: 85 / 137

Model 2520 Pulsed Laser Diode Test System Service Manual Troubleshooting 4-13
Troubleshooting
Troubleshooting information for the various circuits is summarized below. Refer to the
component layout drawings at the end of
Section 6 for component locations.
Display board checks
If the front panel display tests indicate that there is a problem on the display board, use
Table 4-1 . See “Principles of operation” on page 4-4 for display circuit theory.
Table 4-1
Display board checks
Step
Item/
component Required condition Remarks
1
2
3
4
5
6
Front panel test
J1033
U902, pin 1
U902, pin 43
U902, pin32
U902, pin 33
Verify that all segments operate.
+5V, ±5%
Goes low briefly on power up, and
then goes high.
4MHz square wave.
Pulse train every 1 ms.
Brief pulse train when front panel key
is pressed. Use front panel display test.
D5V supply.
Microcontroller RESET.
Controller 4MHz clock.
Control from main processor.
Key down data sent to main processor.