Author Topic: Fluke 8840A  (Read 258 times)

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Offline Maruku

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Fluke 8840A
« on: February 18, 2020, 09:02:57 am »
Hi folks,

So I saved one of these from the skip the other day and finally got around to try and fix it. It came back from ETC as faulty and not worth repairing, last calibration was done in 2014 with restricted usage on the 200 and 2000VDC range (non-functional).

Took it apart and found the fuse resistor "network" Z302 (P/N: 655852; 9M9 and 100k DC input divider). The 9M9 was open so that will need replacing, for the time being I used a high voltage 10M resistor there. Does Fluke still supply replacement components for these?

Also wanted to check the supply voltages whilst trying to fix the unit and the -15V rail is a bit off (table in attachments).
Measured the big regulator caps and they seem to be fine, not sure about DCR don't have a meter for that. I also measured ripple on all rails with a AC millivoltmeter and had 4-6mVRMS on all rails.
Should I start checking for voltage drops on components using the -15V rail? Tantallum caps possibly?  :-/O

Finally I wanted to test the calibration, so I have pressed the CAL switch, wait for the first cal which is short, press the STORE button and I get an error 42 (Calibration memory write error.)
Any experience with that anyone?  :-//



Offline lowimpedance

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Re: Fluke 8840A
« Reply #1 on: February 18, 2020, 10:43:18 am »
This model is long obsolete and the only spares available come from other 8840a 's.
Why bother with the calibration if the input divider is shot, whatever it was before is now no longer valid anyway.
If you manage to find another parts unit you might end up taking bits from this one to fix the other 'parts' unit assuming the input divider is good and cal has not been played with.

edit : corrected a typo!.
« Last Edit: February 18, 2020, 10:02:04 pm by lowimpedance »
The odd multimeter or 2 or 3 or 4...or........can't remember !.
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Offline Maruku

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Re: Fluke 8840A
« Reply #2 on: February 18, 2020, 02:37:48 pm »
Thanks for the info, appreciate it.

Shame the parts aren't available anymore, its only the 200V and 2000V range that is off anyway.
Wonder if the error 42 may be a common fault and someone else has managed to fix that.


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