obnoxious Fluke 87 V meter problem

[Cydrome Leader]

[...]

I just confirmed that just one breath like one would use to clean
eyeglasses is enough to "short out" the small current range jack.

Can anybody else try this?

I'm going to ask fluke about this.

Doesn't happen with mine. Serial # is 96800437.

OK, I checked my 87-5. DOES NOT trigger the lead warning by any amount of
close-up hot breathing into it.

I got an RMA today for mine.

The tech support guy was basically able to cut me off before I described
the problem, and suggested I clean the jack with pure alcohol, which I
tried already. That didn't work so it's going back. It was hinted it would
take years of grime to build up on the jack before it acts weird, which
obviously isn't the case.

Also checked my 289 again to confirm "Made in America".

It is, "of U.S. and non-U.S. components" - about as I expected.

So it's back to the 73 series II for now I guess.

I'm really curious as to what the resistance is between the "shorted"
contacts, but I can't measure it without desoldering the jack, which would
probably cancel any warranty work on the unit.

 

[Mark Zacharias]

[...]

I just confirmed that just one breath like one would use to clean
eyeglasses is enough to "short out" the small current range jack.

Can anybody else try this?

I'm going to ask fluke about this.

Doesn't happen with mine. Serial # is 96800437.

OK, I checked my 87-5. DOES NOT trigger the lead warning by any amount of
close-up hot breathing into it.

I got an RMA today for mine.

The tech support guy was basically able to cut me off before I described
the problem, and suggested I clean the jack with pure alcohol, which I
tried already. That didn't work so it's going back. It was hinted it would
take years of grime to build up on the jack before it acts weird, which
obviously isn't the case.

Also checked my 289 again to confirm "Made in America".

It is, "of U.S. and non-U.S. components" - about as I expected.

So it's back to the 73 series II for now I guess.

I'm really curious as to what the resistance is between the "shorted"
contacts, but I can't measure it without desoldering the jack, which would
probably cancel any warranty work on the unit.

DC resistance between split halves of current jacks on the 87-5 = 2.4 meg

on the 85-3 it is 30 meg on mA jack, 25 meg on Amp jack
..
The 289 appears to use optical sensing.

Mark Z.

 

[Cydrome Leader]

[...]

I just confirmed that just one breath like one would use to clean
eyeglasses is enough to "short out" the small current range jack.

Can anybody else try this?

I'm going to ask fluke about this.

Doesn't happen with mine. Serial # is 96800437.


OK, I checked my 87-5. DOES NOT trigger the lead warning by any amount of
close-up hot breathing into it.

I got an RMA today for mine.

The tech support guy was basically able to cut me off before I described
the problem, and suggested I clean the jack with pure alcohol, which I
tried already. That didn't work so it's going back. It was hinted it would
take years of grime to build up on the jack before it acts weird, which
obviously isn't the case.

Also checked my 289 again to confirm "Made in America".

It is, "of U.S. and non-U.S. components" - about as I expected.

So it's back to the 73 series II for now I guess.

I'm really curious as to what the resistance is between the "shorted"
contacts, but I can't measure it without desoldering the jack, which would
probably cancel any warranty work on the unit.

DC resistance between split halves of current jacks on the 87-5 = 2.4 meg

on the 85-3 it is 30 meg on mA jack, 25 meg on Amp jack
.
The 289 appears to use optical sensing.

Interesting- I'll test resistance with HP 34401 (which has been mostly
surprise free except for the really low input impedance of the AC ranges)
before I ship it off.

Yesterday was less humid in the house, and it took an extra puff to
trigger the lead error, but it was still easy. Maybe the shroud of the
jack uses a water absorbing plastic like nylon.

 

[William Sommerwerck]

Yesterday was less humid in the house, and it took an extra puff to

trigger the lead error, but it was still easy. Maybe the shroud of the
jack uses a water absorbing plastic like nylon.

Maybe there's some hygroscopic shmutz around the jacks. Have you thoroughly
cleaned/flushed the area?

 

[Cydrome Leader]

Maybe there's some hygroscopic shmutz around the jacks. Have you thoroughly
cleaned/flushed the area?

yeah, it's clean, plus it's basically new. I've not been dragging it
around a steel mill or anything like that.

 

[William Sommerwerck]

Yesterday was less humid in the house, and it took an extra puff

Yeah, it's clean, plus it's basically new. I've not been dragging it
around a steel mill or anything like that.

This has puzzled me ever since you first posted.

CMOS is sensitive to surface contamination -- anything that's conductive,
even only slightly including water.

You might try hitting the area with freeze spray. This ought to reveal two
things... First, is the problem caused simply by blowing on the board (ie,
moisture has nothing to do with it). Second, the low temperature will cause
moisture to condense. Does the problem occur after the spray has evaporated?

If I had access to an ultrasound bath, I'd dunk the board in an inert
solvent and clean it thoroughly. If that didn't clear the problem, I'd be
surprised.

 

[Cydrome Leader]

This has puzzled me ever since you first posted.

CMOS is sensitive to surface contamination -- anything that's conductive,
even only slightly including water.

I've decided not to mess with the inside of the meter itself. It's under
warranty, and clearly screwing with it won't help me out in this case. The
board itself looks clean- none of that white dust you see on crappy board
with water based flux or whatever causes that. Just blowing on the jacks
with the meter close will cause the lead error, although today it's harder
as it's less humid out. Maybe there's some factory included contanmination
on the PCB itself, so that the extra gigaohm of my breath is just too much
for it.

I did measure the resistance of the current jack, which was about 1.8M and
it changed as if there was a cap in the sense circuit. There were visible
1M resistors connected to the sense side of the current jacks.

You might try hitting the area with freeze spray. This ought to reveal two
things... First, is the problem caused simply by blowing on the board (ie,
moisture has nothing to do with it). Second, the low temperature will cause
moisture to condense. Does the problem occur after the spray has evaporated?

If I had access to an ultrasound bath, I'd dunk the board in an inert
solvent and clean it thoroughly. If that didn't clear the problem, I'd be
surprised.

Fluke seemed keen on getting in for repair, so we'll see what they do to
it.

 

[William Sommerwerck]

Fluke seemed keen on getting in for repair, so we'll see

what they do to it.

Please let us know. I like to hear solutions to odd problems.