Fluke 8800A - quick question about fault

[qu1j0t3]

Noob here, just bought a nice clean Fluke 8800A from ebay… Just powered this one up and before I even get to making a reading, there seems to be an issue. On DC 20V range, the display starts at -0.0000 but immediately starts counting in the negative direction without stopping, about .005V per second. Does this problem sound familiar to anyone?

I'm getting hold of the schematics. Haven't popped it open yet. Thanks for any clues.

[bitseeker]

Welcome to the forum!

Edit: See edavid's and bd139's posts, below.

[edavid]

It's not a fault, it's totally normal for a high impedance voltmeter.

[bd139]

For ref, 8800A on 20v range is quoted as >1000M impedance. Only on 200v and above it will probably not drift as that's 10M. As edavid says - normal

Also, nice meters!

[bitseeker]

Interesting. On other high-impedance meters I get the values dancing around (noise), rather than building up (or down, as the case may be).

[bd139]

My 8600A just climbs and climbs. It's probably picking up the stress electrons coming off me.

[bitseeker]

LOL, I guess seeing it climb adds to your stress. Positive feedback!

[qu1j0t3]

OK, glad I flagged myself as noob, then.

Thanks for the excellent and very fast replies, everyone.

[bitseeker]

No worries. There's so much to learn, we're all noobs at something or many things. That's what the forum is for, sharing knowledge.

[switcher]

These are excellent excellent excellent meters. I like mine so much, I bought another one...

[bitseeker]

OK, I figured out why I didn't see this behavior on a regular basis. By default, the input impedance on my Keithley and HP meters are high, but not in the >1 or >10 GOhm range. Changing them (either via menus or manually ranging) then yields the constantly drifting value with no input.

My Fluke 8100A is too old. Its impedance is fixed at 10 MOhm on all ranges.

[qu1j0t3]

I am missing a couple of the input shorting bars, though, if anyone knows a source.

[alm]

Try Pomona 4115. They are fairly expensive (approximately $3/ea).

[qu1j0t3]

Thanks @alm That looks like the ticket... https://www.digikey.ca/product-detail/en/pomona-electronics/4115/501-1505-ND/736747

[switcher]

I think the earlier ones are nicer, the keys are more 'square' Later ones have more 'pointy' keys.

[bitseeker]

Yeah, they have their pros and cons. That's why you can't have just one (or two, or three, or ...)

[bd139]

N+1 is the magic number

[qu1j0t3]

Reading other Fluke threads, it seems like electrolytic cap replacement is often recommended. Is this something I should do right away on this meter?

(I've done a fair bit of cap replacement on other supplies and inverters.)

[bd139]

Might be an idea. A couple of mine have had leaky ones in and they make a mess of the board.

[qu1j0t3]

I opened it up, caps are clean as a whistle…