I am sorry to post a non HP/Agilent question here. I just want to
know if anyone can help me finding the root cause of my 8842A problem.
When the meter is powered on, it stuck in rolling reset. The display
first come on ok, but it blinks in about every 1.2sec. It has no
reponse to any key input. Pressing SQR button for 3sec will not
trigger it to go to diagnostic mode neither.
With the help of the service manual, I discovered U202 Z8 CPU doesn't
have 80Hz pulse input on pin 39. I believe the signal comes from
U101, the Fluke proprietary A/D chip which has long been out of
production. It is like a dead sentence to my meter.
I have checked all DC supply lines and they are all within spec.
I also believe the meter stuck in rolling reset is because of the
watchdog timer times out every 1.2sec due to inactivity on CS7
according to the service manual. Unfortunately the service manual
doesn't have schematic of the U101 A/D chip input and output.
I'll appreciated it if anyone can help me how to diagnose the issue.
Tom
