EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: salbayeng on July 05, 2016, 09:50:04 am
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I found an old post on this topic,
https://www.eevblog.com/forum/testgear/fluke-8840a-bench-multimeter/ (https://www.eevblog.com/forum/testgear/fluke-8840a-bench-multimeter/)
And my 8840 had the same problem, basically you turn it on , it would run for 5 minutes then stop (go blank, relay clicks) then start again, sometimes it would restart in few minutes and then stop again.
If you wriggled the case it would restart again. With the cover off , it would work if you pushed down on the piggy back ROM on the CPU (U202) , and stop if you pulled up on it.
With some difficulty I replaced the 40pin CPU socket with a nice machined pin socket and though I had fixed it, but nope 10 minutes later, playing up again.
I pulled the ROM out, and polished the legs using one of those rubbery abrasive blocks, pushed it back again, working again?... nope.
I was getting ready to jam a 20pin machined pin socket into the piggy back one (figuring out the wider pins would make better contact, when I thought, the plastic bit looks removable, so I gently levered it off (with an IC extraction tool) , and :wtf: , two sockets came away with the carrier! (see photo)
A little flux and some very average soldering, and the contacts were back together (see photo).
Working fine now no matter how hard you push and pull.
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Resolder ALL of the mains power transformer connections at the main board. It's easy to miss a couple. The connections might look ok but still not be. Fixed mine.
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That's a good point, that I found in the earlier post .
The first place I checked was the transformer, as I found pushing and pulling on the power transformer would sometimes cause my problem.
With a naked eye, the transformer joints looked good, but with a microscope you could see fairly poor wetting, I fixed all these joints with some good flux and good solder, and lots of scrubbing with soldering iron tip, but it didn't fix my problem. I also noticed the power rails stayed constant when the 8840 dropped out.