Electronics > Repair
Fluke 87-1 Constant beeping, stuck in V AC and no measurement possible
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Wildsau96:

--- Quote from: Shock on May 14, 2024, 11:55:19 pm ---Do you have details about the onset (how it came to be not working)?

--- End quote ---

I got it from a colleague. „One day i turned it on and it started beeping and didn‘t work anymore“. The meter didn‘t have a hard life. More or less just stationary use in a laboratory.


--- Quote from: Shock on May 14, 2024, 11:55:19 pm ---
Please do look at (test resistance) and clean the input jacks. They leak across to the lead detection or become intermittent, high resistance. If you are using the jacks to take measurements you could get erroneous measurements. Better idea to solder or hook a wire on the pcb somewhere. I've cleaned up a similar problem on a 179 and it was input jacks and dirt on the pcb. If you ever see dirt while cleaning the input jacks high chance a contamination issue existed. In the past I've used an IPA soaked cotton bud with some of the cotton unwound. You have to clean until it comes out spotless after several attempts.
 
AC will bounce around a little until you short the leads together then it should zero.

--- End quote ---


I already cleaned the jacks several times. Cotton buds stay spotless, when i insert them soaked in IPA. I also resoldered the pins of the jacks. There are no shorts in the lead detection.
I also bathed the whole board in IPA for several hours and scrubbed it down with a toothbrush.
I do all my measurements connected to the COM jack of the 87. But i can repeat the last ones and take the ground from somewhere on the board.

Edit: All the measurements are the same when taking ground from the board
Wildsau96:
I resoldered R42 and C34 to the board (The trace near U4 pin 87 is still cut)
Now i get a voltage from AP6 to COM of -178,9 mV. So everything seems fine there.
daisizhou:
The focus of cleaning is the yellow area
alanep:

--- Quote ---I resoldered R42 and C34 to the board (The trace near U4 pin 87 is still cut)
Now i get a voltage from AP6 to COM of -178,9 mV. So everything seems fine there.
--- End quote ---

That indicates the only place the extraneous leakage can be coming from is U4 pin 87 or whatever remaining pcb trace that's connected to it. If the trace is short, it's starting to look awfully like U4 might be stuffed given I believe, U4 pin 87 is an input. There's probably no point doing the 68K load test.

Interestingly, U4 pin 87 is very close to the U4 pins used as lead detection/sense for uA/mA/A i.e. pin 88 (AP5), pin 89 (AP4). Perhaps there was some kind of flash over due to crud between the terminals etc at some stage...
Wildsau96:
I cleaned and inspected the area around the remaining trace of pin 87 extra carefully again. I can‘t find anything that indicates a leakage.
It‘s hard for me to say that, but i declare U4 for dead.
Since i‘m not able to lift U4 from the board (and the prices for a working chip are pretty high), i declare the whole meter as a parts donor.
Thanks to everyone who helped me narrow down and find the problem! Without you, i would still stare at the schematics and the board, trying to understand the workings of it  :-+

If someone needs a parts donor Fluke 87-1 in or around germany, he can pm me.
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