Fluke 8024 repair

[Tom Bavis]

First the back story... 25 years ago i worked for a small RF communications company, and at various times I was in production test, design, test engineer, cal lab - we had a bunch of Fluke 8022s and there were only two problems I recall - segments would go out on the display and the Ohms protection MOV would get blown a lot.  The first was fixed by cleaning the PCB and display contact and the second by rewriting the transceiver test procedure so that the +800V supply wasn't the first measurement after the (power-off) Ohms checks.  A few years ago, I bought a Fluke 87 at a garage sale that had a few segments out and had it fixed within a few minutes.  That's the extent of my Fluke repair knowledge.

Flash forward to 2013.  I bought a $5 Fluke 8024B (not really expecting it to work...) and two weeks later found another 8024B with a fuzzed out display (also for $5).  Both of these show an offset of about 20-40V, reads the same on different ranges, so I guess it's ahead of the range switch.  My first guess is circuit board leakage due to failed electrolytics - but if anyone has seen this symptom, I'd like to hear about it.

[retiredcaps]

My first guess is circuit board leakage due to failed electrolytics - but if anyone has seen this symptom, I'd like to hear about it.

Both ModemHead and I have experienced failed/leaked caps on the Fluke 8060A.  ModemHead documented the process and found some other problems in his blog at

http://mrmodemhead.com/blog/fluke-8060a-repair/

His blog also contains various other multimeter repairs.  It is well worth reading. 

[retiredcaps]

BTW, schematics at

http://www.ko4bb.com/Manuals/Fluke/Misc/8024B_Manual.pdf

I also forgot to mention that one of the caps that leaked and wicked its way up the ACV calibration pot. It took a few full turns of the pot to make it work again.  It took several days for me (with generous help from ModemHead) to track down the problem, but I learned a lot in the process.

[Tom Bavis]

Looked at the schematic and didn't see any large value caps.  I suppose an error in the reference voltage would give a proportional error, not a offset.  But the auto-zero circuit would be an offset... could be more than one thing wrong too, but DC volts is the simplest, figure out what's wrong there and maybe I have it.

[lowimpedance]

 I have had similar problems with offsets and drifting in an 8020b due to pcb contamination as a result of electrolyte leakage from those minature electrolytics.
While I cannot recall either what electrolytics if any have been used in the 8024, they have been a real pain in the 8060 and 8020b.
They will be physically small and generally all will be leaky. Have a good look inside for these minature electro's and if found replace after a very
thorough clean of the PCB and hopefully there will not be too much damage to the copper traces!!.

[retiredcaps]

C3 sits on the switch pcb assembly and C10 sits on the main pcb are both 22uF 16V electrolytic caps (as per parts list).  C10 sits right next to U12 the thickfilm resistor network.

On my 8060A, some leaky caps were not obvious.  It wasn't until I removed them that I saw the electrolyte on the pcb.  That is, it leaked from the bottom bung.  As ModemHead and lowimpedance suggest, a good IPA cleaning is recommended.

PS. I'm still learning how a multimeter works so hopefully, I'm not leading you on a wild goose chase.

[ModemHead]

I'm late to the party, it appears...   

Definitely PCB contamination is the #1 possibility.  The only thing I can add to the discussion is that it doesn't even take a leaky electrolytic cap, sometimes just enviromentals will deposit a film on the PCB that leads to offsets.  Generous use of IPA and a toothbrush is the remedy.

If U8 is socketed, take it out and scrub it too.  Believe it or not, I ended up reviving my 8060A MAC chip (the one in the blog entry) that way.

[Excavatoree]

Thanks for the tips.  Maybe I'll try and fix some of my (button-less, ha ha) 80xx series meters.

[retiredcaps]

Maybe I'll try and fix some of my (button-less, ha ha) 80xx series meters.

While I'm still learning, I would happy to assist in troubleshooting if you start a new thread for your meters.