Electronics > Repair

Fluke 8840A Faulty CPU

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Kjo:
There are very few versions of the manual for the 8840A (12/91 revised 5/97), and it is incomplete in terms of schematics. But you can combine it with the 8842A (12/91 revised 7/96) which is complete.
The main PCBs are slightly different, and some of the option boards are jumpered  specific to the 8840A/AF (AC Converter) and/or have different ROMs (488 card) but the schematics are the same.

But I know of no material changes to the main PCB from 1984-85 to 1997-98. Your meter may have been re-caped, but of the 30 meters I have tested, I found only 2 that needed new caps (and not all of them).
I dont subscribe to the "re-cap" everything, particularly industrial equipment. I typically measure, with a pair of HP3457A scanning system meters), AC & DC values of the 6 main input filter capacitors
and the 10 regulated DC supplies. If these meet the Fluke specs I dont tough them.
The only thing I have found that changed is the supports under the main PCB in the transformer area. Meters up to about 1988 have only a white nylon hex standoff to keep the PCB from sagging. Later
models have a machined Delrin transformer support. I suspect a known failure was de-laminating of the transformer solder joints. (I always re-solder the transformer if I poen a meter.)

kjo  KO3Y

eric.niu:
Z86E11 and Z86E21 from ST works for sure, I already tried few.

Kjo:
If you can find them in good working order. Virtually all you see on eBay are removed from equipment. About 15-20% of my aqusitions are faulty in some way. Either they will not program or one or more I/O pins are faulty.

Not too many hobbyists have the capacity to program the EPROMs in these let alone actually test the functionality of a microprocessor. The closest is some application that is known to use all of the I/O pins is a rigorous manner. Fortunately, I think the 8840A/42A main processor code gets close to this if you run the 21 built-in self-tests with both the AC and GPIB adapters attached.

It is also interesting that the ST Z86E11 & 21 EPROMs program very differently than the original Zilog Z86 OTP devices. And I have never seen a Zilog programmable device with a window…

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