Cleaning, testing, calibrating an 8050a

[magconpres]

I picked up an 8050a of FleaBay for $35 shipped.

Upon arrival, the display wasn't working, but after letting it charge all night it came on the next day, but was displaying random stuff.

Before returning it, I thought I'd try new batteries, and that seems to have done the trick, but it still isn't perfect.

in the 200mv DC setting, I get a reading of about .01 mV with nothing being measured.  At times this will drift up to about .10, but then comes back down.  If I short the probes, it sites at .01mV.

Similar, shorting the probes on the 200 Ohms setting shows about .06 Ohms on the display.

Comparing measurements of voltage and resistance with my handheld Extech EX300 shows between a .2 to .4% difference in resistance measurements across various resistances.  about .3% for DC Volts (testing some batteries), and 2.7% on AC volts (120V mains).

The offset doesn't bother me much, but the fact that the voltage drifts around makes me think somethings up.

For now, I plan to clean up the board with some contact cleaner and will plan to replace the PS Caps to see if that tightens things up a bit.  From reading threads on this forum, that seems to be standard practice for these older units.

Hoping that addresses the issues.  The buyer will take it back, but I suspect this is in fact 'in working order' as described and just needs some TLC.

Looking for any input from others on what to investigate or do while I have it opened up.

James

[med6753]

I had similar issues with an 8010A that would drift high over time on DCV. Turned out to be board contamination. Your issue could be the same. Fluke recommends the following process and I did it and it works....

Remove the LCD display.
Scrub the main board both sides with 100% IPA.
Bake the board at 150 degrees F (65 C) for several hours.

[Fungus]

I had similar issues with an 8010A that would drift high over time on DCV. Turned out to be board contamination.

It could also be the capacitors on something that old.

I'm sure that baking at 150 degrees will kill off the bad ones, maybe make them discharge their electrolyte all over the PCB.

[med6753]

I had similar issues with an 8010A that would drift high over time on DCV. Turned out to be board contamination.

It could also be the capacitors on something that old.

I'm sure that baking at 150 degrees will kill off the bad ones, maybe make them discharge their electrolyte all over the PCB.

The board clean and bake was AFTER the power supply was re-capped and any suspect tantalums replaced.

[Fungus]

The board clean and bake was AFTER the power supply was re-capped and any suspect tantalums replaced.

That little detail was missing from your procedure. 

[magconpres]

I had similar issues with an 8010A that would drift high over time on DCV. Turned out to be board contamination.

It could also be the capacitors on something that old.

I'm sure that baking at 150 degrees will kill off the bad ones, maybe make them discharge their electrolyte all over the PCB.

The board clean and bake was AFTER the power supply was re-capped and any suspect tantalums replaced.

The power supply caps seem straight forward enough, as does the cleaning.  But, with regards to "suspect tantalums", is this just a visual check or do I need to start measuring each cap?

[Fungus]

is this just a visual check or do I need to start measuring each cap?

Measure.