Killed my Fluke 87 III

[defaced]

This is more of a feeler thread right now. In my infinite wisdom, I attempted to read my 560VDC B+ voltage with my Fluke 87 III set to resistance. After the sparks flew (literally at the probe to B+ contact point), the meter still reads, but voltage readings are low by about two orders of magnitude; I haven't diagnosed the other settings. I've found a schematic on Fluke's site, but I'm not making much sense of it. Is there a Fluke repair group out there (Yahoo group or forum), or would one of you be willing to hold my hand while I attempt to repair this (if possible)?

[Prairie Dawg]

Originally Posted by defaced

This is more of a feeler thread right now. In my infinite wisdom, I attempted to read my 560VDC B+ voltage with my Fluke 87 II set to resistance. After the sparks flew (literally at the probe to B+ contact point), the meter still reads, but voltage readings are low by about two orders of magnitude; I haven't diagnosed the other settings. I've found a schematic on Fluke's site, but I'm not making much sense of it. Is there a Fluke repair group out there (Yahoo group or forum), or would one of you be willing to hold my hand while I attempt to repair this (if possible)?

Duid you check to see whether you blew the internal fuse in it?

[Steve Conner]

This has happened to me before. It fried the main chip inside the meter, and I had to throw it away.

That was with a cheap no-brand DMM though, and Flukes are supposed to be tough.

So, check internal fuses as suggested. Also check the schematic for any protection devices such as MOVs, TVS diodes, clamping diodes or the like. A good meter should have these, and one of them might have blown out, giving its life to save the chip.

[Robert M. Martinelli]

Hi all,
Steve's right, Flukes are really tough, and I think Fluke included something in the circuitry to protect the meter from misusing it ( I think we all burned a DMM at one point in our lives, I did it too, and I'm not ashamed to tell, as they say, you live, you learn ).

Since the reading you're getting are low by two orders of magnitude, I would expect something in the selectable voltage divider has gone south ( the meter's processor should normally select the appropriate divider ratio ). Usually there are several 10x scaling resistors, namely, 909 K, 90.9 K, 9.09 K, 909 Ohms....etc. possibly enclosed in a plastic envelope ( array ).

Hope this helps

Best regards

Bob

[Enzo]

Your title says Fluke 87 III, while your post says Fluke 87 II. WHich is it? Can you link the schematic to the right one?

[defaced]

I'm 90% sure it's a III, but I will double check. Right now I can't seem to put my hands on the schematic on Fluke's site, so I'll work on that tonight after work.

[Prairie Dawg]

Originally Posted by defaced

This is more of a feeler thread right now. In my infinite wisdom, I attempted to read my 560VDC B+ voltage with my Fluke 87 III set to resistance. After the sparks flew (literally at the probe to B+ contact point), the meter still reads, but voltage readings are low by about two orders of magnitude; I haven't diagnosed the other settings. I've found a schematic on Fluke's site, but I'm not making much sense of it. Is there a Fluke repair group out there (Yahoo group or forum), or would one of you be willing to hold my hand while I attempt to repair this (if possible)?

this is a little after the fact but that's a good argument for doing preliminary measurements with something you can dedicate to the task and toss if you burn it up. I've got a $5 Cen-Tech DMM that I use for measuring B+ voltage and nothing else. That way the good stuff doesn't have the risk involved.

[defaced]

Looks like 90% positive means you're 100% wrong. I have a Fluke 87 (no roman numerals), the board is dated 1986, so I'd say it's of the right vintage. Service manual is 12MB, so here's the link to Fluke's site that has it:
http://assets.fluke.com/manuals/83_85_87smeng0500.pdf

Layout and schem starts on PDF page 83.

Both fuses test good, 0.2 ohms and 0.8 ohms.