Author Topic: Fluke 87 III misbehaves  (Read 8707 times)

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Offline andyrew

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Re: Fluke 87 III misbehaves
« Reply #25 on: March 17, 2020, 08:52:59 pm »
i dont have a variable ps at the moment so i just hooked up the 9v battery and tried to take a couple measurements. i'm getting 6.6v across vdd and vss and about 3.2 across each of them independently. i'm also seeing a current draw of about .2mA with no screen.

do you have a map of where i can check the voltages in fig 3-14? i can find the points on the schematic but i cant translate into physical locations (they're too small :) do the TPs match up to the voltages listed somewhere?
 

Offline andyrew

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Re: Fluke 87 III misbehaves
« Reply #26 on: March 18, 2020, 08:15:15 pm »
i asked the people at fluke what the problem with this might be and they told me their technicians are telling them that this is a fatal error. they think the problem lies within the processor. if that's the case the only way to fix it would be the replace the processor and i'm pretty sure they don't make them anymore  :)

If anyone has other ideas please let me know as i'll be very sorry to trash this meter
 

Offline shakalnokturn

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Re: Fluke 87 III misbehaves
« Reply #27 on: March 18, 2020, 08:34:36 pm »
Fluke could be right but you're the one who can actually do the most testing.

If you're sure of the switch contacts, battery connection and wires, my next suspects would be the tantalum drop capacitors. It could also be worth the trouble of reflowing the ASIC.
 

Offline andyrew

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Re: Fluke 87 III misbehaves
« Reply #28 on: March 18, 2020, 08:38:32 pm »
i assume to test the capacitors i need to remove them from the board?
and i assume by ASIC you mean the main processor?
 

Offline shakalnokturn

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Re: Fluke 87 III misbehaves
« Reply #29 on: March 18, 2020, 10:17:19 pm »
i assume to test the capacitors i need to remove them from the board?
and i assume by ASIC you mean the main processor?

Tantalum drops sometimes show "intermittent" behaviour so  this is one of the rare cases where in doubt I just replace them. (I test them out of circuit on the oscilloscope's component tester, I'm not sure how/if the intermittent failure shows on other testers though.)

Yes, that's what I meant by ASIC.
 


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