Author Topic: Yet another Fluke 8842A transformer solder fail  (Read 1545 times)

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Online LazyJack

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Yet another Fluke 8842A transformer solder fail
« on: July 19, 2016, 09:20:07 pm »
Couldn't resist to get a cheap  Fluke 8842A from eBay. It was advertised as powering up, without the display. Since it was loaded with the AC and GBIP options and was in a very nice physical condition, I figured, even if it is very dead, I would able to source an other instrument and make one from the two, with all the options.
I first looked into it, did not see any visibly obvious, so tried powering up. The relays clicked and they also clicked when changing ranges, so at least for some extent it was working, but no display at all.
Components had 1988 datecodes, so it's not exactly young, but at least not older than me. 
Next step is to check voltages. They all looked ok on the main board, except the VFD filament voltage, which should have been 4.5VAC, but was zero.
OK, so the first usual suspect, the transformer. pins 14-16 are the filament, and bingo! As soon as nudging it with the probe, the display flashed.
Lets get the soldering iron and resolder all pins. It was really hard to do, once reflowed the solder, on some pins it actually separated from the lead, was not wetting at all. Remove solder, srape pins, it was now possible to properly wet and solder.
Turn on, display works, all self tests are passed. Fortunately the VFD is of good brightness (not on the picture, because of the flash), the instrument is pretty clean and tidy inside an outside.
I'll need to check the accuracy, but first checks show it is not way off at least.
I am satisfied and happy.
 
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Offline mzacharias

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Re: Yet another Fluke 8842A transformer solder fail
« Reply #1 on: July 19, 2016, 10:26:09 pm »
My 8840A - virtually same story. Often the bad solder connections are hard to tell visually. Common problem, I guess.
 

Online LazyJack

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Re: Yet another Fluke 8842A transformer solder fail
« Reply #2 on: July 20, 2016, 04:46:06 am »
All right. I tested all functions and ranges and pretty much matches up to the Fluke 87. Of course this should be done the other way around, but I don't have anything more precise than the 8842A. But at least it shows that functions work and they are likely very close (maybe even in) to being in spec.
The GPIB also works, so it's now possible for me to set up long time measurements and data acquisition.
The ultra high input impedance voltage ranges are also pretty cool. Really nice instrument.
I think it was worth the 70 bucks.
 

Offline lowimpedance

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Re: Yet another Fluke 8842A transformer solder fail
« Reply #3 on: July 20, 2016, 10:38:08 am »
Good score for 70 bucks,...... perhaps this thread could have been just an addition to this one.

https://www.eevblog.com/forum/repair/what-was-your-easiest-repair-ever/

Still always good to see good old gear being saved from landfill..........enjoy.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 


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