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Author Topic: Multimeter with bad probe connectors  (Read 1053 times)
AG4DG
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« on: September 15, 2010, 10:07:03 PM »

I have a DMM with bad probe connections.  Even with new leads, I still don't always get continuity/0 ohms when I touch the probes together UNLESS I really press the leads into the multimeter.

In other words, the leads aren't the problem - it's the point at which they connect to the circuit inside the DMM.  I think there is corrosion here.

Have any of you fixed a DMM that had this very problem?  Unfortunately, the connector inside seems to be glued in place.
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AD5X
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« Reply #1 on: September 16, 2010, 03:40:38 AM »

Sounds mechanical, so open it up and see what the problem is.  Either a bad solder connection, or a loose screw if that is what is holding the jacks to the pc board.  I got a very nice benchtop DMM for a great price because it was intermittant.  In my case, the jacks were attached to the pc board with screws, and one jack had a loose screw.

Phil - AD5X
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KG8JF
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« Reply #2 on: September 16, 2010, 05:14:51 AM »

Unless it is a Fluke, just buy a new multimeter.  They are so cheap.  They can be had for as low as $5.00 up to about $20.00.  Generally, when we use a meter we are looking for the presence of a voltage or signal.  We do not need the fractional value. Smiley
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WA3SKN
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« Reply #3 on: September 16, 2010, 05:16:31 AM »

You either go in, fix the electrical problem, then use glue to fix the physical problem... or just buy another meter.  They are just not too expensive, anymore.
I usually like to try and fix things, though.  It can become a challenge!
73s.

-Mike.
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KS3J
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« Reply #4 on: September 16, 2010, 10:09:32 AM »

If it's a good multimeter like a Fluke, Simpson, or Beckman, it's probably worth repairing.  Look for loose fittings (screws, nuts, setscrews) or (if the banana jacks are soldered to the board) for annular cracks in the solder.

If it's a cheapie, it's probably NOT worth spending much time on. I strongly recommend that anyone doing serious electronics work eventually get themselves a Fluke, even if it's old and secondhand, since this is one of the most important tools you will own.  Flukes last forever and hold their accuracy well.
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AD4U
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« Reply #5 on: September 16, 2010, 10:10:40 AM »

Just remember - when buying a cheap DMM for $10 - $15, even if the LCD display reads out in 4 or 5 digits, it definitely does not mean the DMM is accurate to that level.

A Fluke (or similar quality DMM) is a good lifetime investment.

Dick  AD4U
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W8AAZ
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« Reply #6 on: September 16, 2010, 10:54:34 AM »

If the probes fit snugly into the jacks, it is probably where they connect to the board.  Maybe a quick solder fix.  Or the jacks might be over sized, which are usually just hollow tubes on many meters. You would have to carefully spread the prongs a bit on the plugs to make a tight connection but do not break them spreading the contact points.  The jacks are often nickel plated and some resistance can build up as the surface oxidises. I have had a habit of occasionally dipping Q tips in pure isopropyl and working them in and out of the jacks till they come out clean.  Dirty or corroded will leave gray stains on the dampened Q tips.  Or if it is worse oxidation, you might have to dip the Q tips in some metal polish paste and work that in and out of there till it shines up the insides.  Then remove any traces of the polish with the alcohol.  Do not put a lot of metal polish on the tips and make a mess that will be harder to get out.  Just a thin coating will work. But I would check the internal conns. first. 
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