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Old 9th June 2009, 10:23 PM   #1
figge77 is offline figge77  Sweden
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Default Fluke 77 service

been thinking about this for some years now. and ill post it here, who knows maybe somebody will answer?.

problem:
got this Fluke 77 in early/mid 90s and been happily using it ever since. but somwhere along the way it has stopped reading Mohms properly.
lets say i take 5Mohm resistor an meashure it. it starts at 5M and counting down. what could be wrong?
i have never tinkered with such a device before. only hifi.
not really much of a problem but i would like to dedicate my better half some attention.

solution:
maybe i should do some service to it. are there any multimeter servicemen here willing to share some knowlage?

regards Fredrik
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Old 12th June 2009, 06:36 AM   #2
dangus is offline dangus  Canada
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I found some Fluke service info at:
Multimeters Fluke

Could you hook up another voltmeter and see what voltage appears across the 5M resistor when it's being measured? That should give some clue.

And, forgive the obvious question, but, does the meter have a fresh battery?
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Old 12th June 2009, 07:02 AM   #3
figge77 is offline figge77  Sweden
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hi!

thank you!

i downloaded some manuals and will try to meashure the voltage as you described this weekend. ill report back here with results.

the battery is fine, should have mentioned that in the first post.

the meter i have is a 77 non MK, old but i like it.

the problem i described only occur in the MOhm range

its been like this for a very long time.

not that i do any meashuring in that range. but its nice to know your stuff is working correctly.
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Old 12th June 2009, 10:15 PM   #4
figge77 is offline figge77  Sweden
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i checked with a second meter and when meashuring a 4,7M resistor with the fluke i get 0,07V over it.
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Old 13th June 2009, 09:50 PM   #5
anatech is offline anatech  Canada
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Hi figge 77,
I used to repair Fluke meters, and calibrate them also. Possibly some of these suggestions may help you.

Clean the banana jacks inside using alcohol only. Cotton swabs work, remove some cotton if the fit is too tight.

Clean the function switch metallic contacts. Alcohol again.

Check and make sure the PCB of you meter is clean. Alcohol would be the cleaner of chose here (like there is any question). Do not clean the entire PCB, or anywhere near the display contacts or IC unless nothing else works. If your display becomes faulty, clean the elastomer gently on both ends and also the PCB contacts and display contacts. The contacts are hard to see as they are transparent. Do not allow your finger oils or anything else to contaminate any surfaces in there.

If none of that works, I would normally resolder the terminals. I think that one was metal cylinders only. This is a job for someone who is very good at soldering and "has the touch".

Meters like the 87 types used a plastic terminal assembly that you just replaced. It used 4 wire connections to the common and volt terminals. Quite advanced for a hand held meter.

-Chris
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Old 14th June 2009, 10:22 PM   #6
figge77 is offline figge77  Sweden
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thanks chris!

i resoldered the terminals and when i was at it all the other joints aswell. cleaned it up best i could. but still same thing.

it seems i lied in the posts before. the problem is not just at M range. i tried a 660k resistor and it showed 600k.
so i suspect the problem starts around 0,5Mohm or so. but at the higher values it cant get a reading it just falls .
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Old 15th June 2009, 02:19 AM   #7
anatech is offline anatech  Canada
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Hi figge 77,
It still sounds like leakage in the range switch or PCB. The 77 is a pretty good meter and might be worth having Fluke look at it. Otherwise, buy a new Fluke.

I had been lucky in that I could fix most of them properly. Usually the only ones I gave up on were things like measuring the current across a 550 VAC circuit. Tends to vaporize the traces and severely mess with everything else. That and when they get squished flat by construction equipment.

-Chris
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Old 15th June 2009, 02:46 AM   #8
troystg is offline troystg  United States
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I don't mean to hi-jack the thread but I figured I'd ask a question since it was relevant.

I spent my graduation money on a Fluke 87 some 22 yrs ago and it still works flawlessly EXCEPT for the screen readout.. It started to fade a few years ago. I have cleaned the screen and PCB contacts and that generally helps but doesn't cure it completely.

How do I clean the pink "pads" or connector cables that tie the two together? Or should I just get replacements?

My 22 yr old fluke, my 21 yr old Ungar heatshrink gun and my 35 yr old Ungar fixed temp soldering station are all still rocking along. They just don't build them like that anymore... I sure hope I last as long as they do!!
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Old 15th June 2009, 02:59 AM   #9
jam is offline jam  United States
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Troy,

The pink pads can be cleaned with an eraser or a small amount of alcohol on a swab. Fixed my 87 several years ago and still works fine today.
If this does not work replace pads.

Jam
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Old 15th June 2009, 03:18 AM   #10
anatech is offline anatech  Canada
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Hi Jam,
An eraser is destructive to the elastomer. So is any form of cleaning, so it must be done gently and using a damp cotton swab. Isopropyl alcohol only (the 99% stuff). It can be purchased at any pharmacy or ordered in. It is not expensive.

Hi troystg,
To clean your display, there are four surfaces for each elastomer to work on. Do both sides of the elastomer ** gently ** using a damp cotton swab only. Then, clean both the contacts on the display and the PCB carefully. Don't be cheap, use a new swab. Be very careful not to allow anything to contact the cleaned edges. Reassemble them as soon as they are dry, don't leave them hanging around while you work on something else. This is also a good time to clean your lead terminals using the same materials. Never force anything into those terminals! Keep cleaning until the swab comes out clean (like cleaning a gun barrel). Again, don't use too much fluid or you will force the materials inside the terminals out onto the PCB. You do not want to do that.

As Jam correctly pointed out, buy new ones if that didn't work. Oddly enough, I did run into one where the contacts had somehow been worn off the glass display, or maybe had some lacquer or enamel on the contacts. It's well worth the cost of a new display if you need one. Your calibration should be close, even though you are well outside the calibration interval (by about 11 times in commercial use). Got your money's worth, didn't you?

Nice meter by the way. I am hoping to repair a junker to I can have one too. The new meters are "closed case calibration", which is really nice. It really helps the high frequency adjustment, which changes even by putting a different top cover on. I had to make a jig in order to "optimize" the calibration on these. It works extremely well.

-Chris
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