Service manual

Service Manual
Keyboard and mouse
Check computer interface by swapping to a known good
keyboard and mouse. If failure still present, check
continuity of keyboard connector SK 11 and ensure that
+5 V can be found on pin 4 and 0 V on pin 3.
Check functionality of inverting buffers in IC 3, check
continuity through R 62 and R 101.
Check REF8M clock at IC58 pin 8 with a digital frequency
meter. Replace IOC IC 58.
Expansion cards
Check through the section entitled System Failure on
page 5-23, tracing all signals through to the expansion
card backplane. If necessary, replace the expansion card
backplane.
5-28 Issue 2, June 1991 Part 5 - Main PCB fault diagnosis