Electronics > Repair
Fluke 87-I repair
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retiredcaps:

--- Quote from: staze on February 20, 2014, 03:14:20 am ---Also with the unit off, and no battery, the two MOVs register as OL both directions (getting somewhere).

--- End quote ---
I take the battery out because I might commit an oops and short something out.  It looks like removing the battery made change in the readings of the varistors.


--- Quote ---R2 still shows as 0.8517M (which seems wrong),
--- End quote ---
My R2 definitely reads 909K in circuit (both ways).  R2 is supposed to be +/- 1%.


--- Quote ---Could you test C20 in circuit and let me know what you get? I get about 0.136nF.
--- End quote ---
I get 0.115nF (no relative mode used) in circuit both ways.


--- Quote ---Interestingly, it is drawing a very small amount of current when turned off... about 9.80uA.

--- End quote ---
This is consistent with modemhead's finding on the Fluke 83 (8.85uA)

http://mrmodemhead.com/blog/fluke-83-dmm-repair/

Same for this Fluke 87 post (at very bottom - 7.5uA)

http://www.edaboard.co.uk/fluke-87-flat-batteries-t268153.html

My own test also shows 7.5uA when in the off position.
retiredcaps:

--- Quote from: lowimpedance on February 20, 2014, 03:24:53 am ---Give the PCB another good clean with IPA and check again.

--- End quote ---
Modemhead doesn't always document all his repairs, but I have firsthand knowledge that he sometimes gives multiple IPA baths to clean the PCB.  Sometimes a stiff clean toothbrush is required and lots of drying time.

I, too, have sometimes needed to give pcbs multiple IPA baths to get rid of contamination that was causing leakage current.
staze:
okay, just cleaned it again, and again... same result. ~9.8uA when switched off. Interestingly, and maybe I'm being oblivious here, but I'm seeing 9V between the negative side of the battery (VDD/GND?) and the COM jack when the unit is switched off. That, to me, seems... wrong.
staze:

--- Quote from: retiredcaps on February 20, 2014, 05:46:02 am ---Modemhead doesn't always document all his repairs, but I have firsthand knowledge that he sometimes gives multiple IPA baths to clean the PCB.  Sometimes a stiff clean toothbrush is required and lots of drying time.

I, too, have sometimes needed to give pcbs multiple IPA baths to get rid of contamination that was causing leakage current.

--- End quote ---

Okay, I'll give it another one tomorrow... but yeah, obviously something is leaking somewhere. Either that, or the switch is toast...
retiredcaps:

--- Quote from: staze on February 20, 2014, 05:48:27 am ---Okay, I'll give it another one tomorrow... but yeah, obviously something is leaking somewhere. Either that, or the switch is toast...

--- End quote ---
If you read the Fluke 83 repair blog, it goes into great detail how the code switch works including diagrams on how to take the code switch off and check for contamination.
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