Keithley 2520, Service Manual, Page: 89 / 137

Model 2520 Pulsed Laser Diode Test System Service Manual Troubleshooting 4-17
No comm link error
A “No Comm Link” error indicates that the front panel display processor has stopped
communicating with the main processor, which is located on the motherboard. This error
indicates that the main processor ROMs (U3 and U4) may require re-seating in their sock-
ets. The ROMs may be reseated as follows:
1. Turn off the power, and disconnect the line cord and all other test leads and cables
from the instrument.
2. Remove the case cover as outlined in “Case cover removal” on page 5-4 .
3. Locate the firmware ROMs, U3 and U4, located on the motherboard. These ROMs
are the only IC installed in a socket. (Refer to the component layout drawing at the
end of
Section 6 for exact location.)
4. Carefully push down on the ROM ICs to make sure it is properly seated in its
socket.
CAUTION Be careful not to push down excessively. The motherboard could
crack.
5. Connect the line cord, and turn on the power. If the problem persists, additional
troubleshooting will be required.