Fluke 87 repair question

[mke]

Hi,
I'm new to the forum but definitely not new to the EEVblog YouTube channel.
I recently purchased a used Fluke 87v for $65. For the most part, the meter works great, the only trouble is in the resistance function it will read 495.5k ohms without any leads plugged in. When you do plug leads in and short them, it works perfectly fine and displays 0.1 ohms. Also in diode test mode, it displays 0.795v. I first checked for any ptc damage but everything seems to be fine (no signs of heat damage or failure) also I tested the 1kohm fusible resistor and it is fine. Then I went ahead and gave the board a thorough cleaning with ipa. But, no luck.
Has anyone seen/had an issue similar to this. I was trying to locate diagrams for the 87 series 5 but I can only seem to find them for the series 1 multimeters.
Thanks in advance!

[retiredcaps]

I recently purchased a used Fluke 87v for $65.

Excellent deal. 

For the most part, the meter works great, the only trouble is in the resistance function it will read 495.5k ohms without any leads plugged in.

It is likely the blue MOVs have failed. See

https://www.eevblog.com/forum/testgear/fixing-a-fluke-87v/

https://www.eevblog.com/forum/testgear/fluke-87-v-mystery-low-impedance-input/

[joeqsmith]

Dave was just saying how reliable these 87Vs are but sounds like another one bit the dust.   0.78 volts sounds like one of the higher speed clamps has failed.  See pictures.  Check the temperature feature as well. 


Sorry but this gateway error has been preventing me from attaching the pictures. 

[alm]

I imagine that Dave's statement was based on mostly using it for extra low voltage (< 48 V) circuits. He does not seem the type of person to routinely use it on > 300 V circuits. The results of using it daily for 600-1000 V circuits might be very different. Never mind that we do not know the history of this particular unit and it may well have been used far outside its specifications.

I am not saying that either statement about reliability is more or less valid, but it would explain the different impressions that people have.

[joeqsmith]

I imagine that Dave's statement was based on mostly using it for extra low voltage (< 48 V) circuits. He does not seem the type of person to routinely use it on > 300 V circuits. The results of using it daily for 600-1000 V circuits might be very different. Never mind that we do not know the history of this particular unit and it may well have been used far outside its specifications.

I am not saying that either statement about reliability is more or less valid, but it would explain the different impressions that people have.

I think it's important to also understand Joe's tests in context.
The Fluke 87V, the most trusted meter on the market, fails every single one of Joe's tests.  According to Joe's tests it's one of the worst meters on the market. Yet I doubt there is a single 87V owner ever who has seen their meter die due to any ESD or pulse overload etc.

[mke]

Forum was down last night so I wasn't able to post this.
In response to retiredcaps:
That's what I had initially thought also. The problem is that it reads ac and dc voltages perfectly fine. The only issue seems to be the resistance function. The blue varistors visually seemed to be fine, no black coating or burnt look as if they were damaged. I went ahead and took apart my other working 87v to test on it's board and I found that, in the resistance function, the known working 87v had 6.5v at the V/Ohm input jack (I had my neg lead on the 9v ground). The damaged 87v had around 2.99v. Looking around the board with my microscope, I didn't find anything that would indicate a component failure.
Since I was stumped, I went ahead and removed all the blue movs from the board and tested them with my fluke 1503, they each read 0.7M ohms.
My next thought was the input jacks, but I removed them and soaked them in ipa, they're fine.
Here's a pic of the high speed clamps, they appear to be intact.

[joeqsmith]

Did you actually test them with the second 87V or just do a visual?  If only visual, I would again suggest you test them. 

Of, if you like, you could do the same trick with the MOVs and remove them.  Running it without the MOVs and clamps will be fine for a quick check.  If meter starts working you at least have narrowed it down.    I would strap in.   

[mke]

I did remove the movs and turned it back on, same issue.
I reinstalled them and tried temp. With no thermocouple, it reads OL. I believe this is normal for this revision (later ones read "Open").

[mke]

Here's some more pics of what I'm getting

[mke]

It's almost as if it's finding a lower resistance path than the input jacks when no leads are plugged in to flow through, then when you short the leads, that has a lower resistance than the other path, which is why it reads properly up to the point where the resistance being measured is more than the resistance of the other path.

[joeqsmith]

I did remove the movs and turned it back on, same issue.
I reinstalled them and tried temp. With no thermocouple, it reads OL. I believe this is normal for this revision (later ones read "Open").

What I was suggesting is for you test the parts making up the clamp.  Visual may not tell you anything.  Test them in-circuit or remove them if you like.   

[joeqsmith]

What happened to Fluke's lifetime warranty anyway?      Let me know what you see.  Diode mode with second 87V, check all three in-circuit. 

[retiredcaps]

Since I was stumped, I went ahead and removed all the blue movs from the board and tested them with my fluke 1503, they each read 0.7M ohms.

Those MOVs should all read infinite resistance so they are definitely bad.

[retiredcaps]

It's almost as if it's finding a lower resistance path

Did you check the rotary switch for something like this?

http://mrmodemhead.com/blog/ideal-carbon-footprint/

[retiredcaps]

I first checked for any ptc damage but everything seems to be fine (no signs of heat damage or failure)

How did you check the PTC?  That PTC should measure around 1.1k ohm.

[giosif]

Maybe a silly thing but could you check the number of calibrations this meter has had (there's a Youtube video on that)?
Maybe someone has played with that and screwed up.

[mke]

Hey Guys,
Sorry to dig this thread up by I finally got some time to take a look at this thing again. I went ahead and removed all three high speed clamps. The meter no longer reads a ghost resistance and correctly reads OL in ohms and diode test mode, though I assume this is due to me manipulating the circuit by removing the clamps. Does anyone have a good method or spec for testing the high speed clamps? Visually they show no signs of obvious failure (ie. heat damage, melted id numbers on top etc.).
Oh, and for the movs I used my fluke 1503 insulation/megger meter.

Thanks for all the suggestions!
Cheers