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Author Topic: Fluke 87 III repair  (Read 2916 times)

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Offline Beer LoverTopic starter

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Fluke 87 III repair
« on: July 19, 2018, 05:08:20 pm »
Hi all,

I have purchased broken Fluke 87 III multimeter, hoping it would be an easy fix (blown fuse...).
mA range fuse is blown (as the seller said), but there is more!
All measurements show lower values than expected.
Ohm range shows 18.28Kohm without anything connected.

There are traces of someone soldering in the trouble fuse area, but nothing seems out of order.
Without knowing what resistor (and other) values should be there, I have no chance of figuring it out without help :)

Thank You in advance,

Beer Lover
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Offline pelule

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Re: Fluke 87 III repair
« Reply #1 on: July 19, 2018, 05:46:10 pm »
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Offline pelule

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Re: Fluke 87 III repair
« Reply #2 on: July 19, 2018, 05:48:33 pm »
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Offline retiredcaps

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Re: Fluke 87 III repair
« Reply #3 on: July 19, 2018, 08:07:14 pm »
Quote from: Beer Lover on July 19, 2018, 05:08:20 pm
Ohm range shows 18.28Kohm without anything connected.
The input protection is likely bad.

Check the PTCs, MOVs and fusible resistor.  I have written about testing all 3 in various Fluke broken/fix/repair threads.

Quote
There are traces of someone soldering in the trouble fuse area, but nothing seems out of order.
Clear focused pictures attached would help us help you.
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Offline Beer LoverTopic starter

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Re: Fluke 87 III repair
« Reply #4 on: July 19, 2018, 08:28:27 pm »
Thank You    pelule and retiredcaps.

Will check tomorrow, now that I have schematics :)
(not that I claim I can understand anything)

Someone has done some soldering/desoldering in the input protection area,
I mean there are flux residue around trough-hole components,
and looks like one leg of smd bridge-rectifier was lifted, then resoldered...

I'll keep You posted for sure :)
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Offline Beer LoverTopic starter

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Re: Fluke 87 III repair
« Reply #5 on: July 20, 2018, 02:12:39 pm »
Update:
Thermistor reads 1.17 Kohm at ~25C
Varistor RV1 reads 10Kohm, RV2 reads 7.7Kohm
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Offline retiredcaps

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Re: Fluke 87 III repair
« Reply #6 on: July 23, 2018, 04:31:55 am »
Quote from: Beer Lover on July 20, 2018, 02:12:39 pm
Thermistor reads 1.17 Kohm at ~25C
Varistor RV1 reads 10Kohm, RV2 reads 7.7Kohm
PTC ok.

RV1 and RV2 are bad.  Remove both and meter might work fine.  Test with low voltage like 1.5V AA cell and try some resistor values to make sure 87 III works.

If meter works fine, replace both varistors.  Other threads have suggested digikey/mouser proper replacements.
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