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Old 15th May 2008, 03:06 AM   #11
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those switches are better than the ones i was describing.... use deoxit on those, and it might work like new. i was thinking of the switches etched onto the PC board and the knob having the leaf spring contacts on it. the ones in the pic are usually pretty reliable and will last a lot longer. cleaning those switches with deoxit should work just fine. the only thing that would NERTS those switches would be a bad case of corrosion with visible green crystals.
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Old 15th May 2008, 03:12 AM   #12
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Will do!

Wish me luck! If it isn't the problem... I'll be back! (with an Austrian accent) I don't see any corrosion so we will see.

Thank you for the experienced guidance!

Regards//Keith
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Old 16th May 2008, 03:30 AM   #13
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Oh well. it was worth a shot.

I spayed and clicked and sprayed and clicked. I can see the contacts and they are clean and fine. Maybe the center contact is bad on the lowest settings or maybe the resistors in the ladder just went? I am not sure which resistors are the ones for the lowest DC settings.

I look forward to any suggestions! Thanks!

Need to use a bullet?

Regards//Keith
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Old 16th May 2008, 10:55 AM   #14
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you might look at the pc board and see if it's cracked or if you have bad solder connnections. the resistors for the lowest ranges will be low value resistors (comparatively speaking, they are usually at least a few megohms), usually in meters they are all 1% or less tolerance. another thing that happens to DMM's (especially older ones) is damage to the input amplifier and ADC from static electricity. i once had a new Beckman DMM go south, just from the static picked up near the face of a TV picture tube. back then DMM's were a new thing, and DMMs were easily damaged by static. the problem has long since almost completely vanished as manufacturers have made the electronics in meters more durable. it is possible that your meter got damaged from exceeding the input voltage (marked in red between the banana plugs) limits if you have measured something that has a low average voltage but a very high peak voltage (like a horizontal output transistor collector on a TV or computer monitor, some of which might have an average voltage of about 200 or less volts, but peak values above 1500V).
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Old 30th May 2008, 05:28 PM   #15
KP11520 is offline KP11520  United States
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So I got to the range selector switch again and put sonme 400 grit sand paper where I could clean the contacts. The switch will not come apart with it soldered into the PCB, even with the e-clip removed. Another blast of residue free contact cleaner.

While open, I checked evenything and the resistors, solder joints and PCB all look perfect.

I turned it on and the three lowest ranges worked again....... for a half hour and right back to the problem.

I knew exactly what to do and with the help of Chris (Anatech), I bought a new Agilent U1242A. Probably one of the best values around for a DMM. He assured me it was the one to get at this price range ($220.00 USD).

I got it yesterday and It is an investment. Truly impressive. Check it out.

Now if only someone can tell me where I can still buy that rotary switch for my Micronta POS.

Back to measuring Idss!

Regards//Keith
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Old 31st May 2008, 02:31 PM   #16
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while those switches are far better than most used on cheap DMMs, they do have their limitations..... if the silver plating was worn off the contacts to begin with, you didn't hurt anything using sandpaper on them. the copper does have a tendency to oxidize quickly. there is a better way to burnish switch contacts (and relay contacts) and that's with a piece of brown paper from a paper bag. glad you bought a new DMM you're happy with. i have an old milsurp Fluke handheld i'm happy with, and also hace a couple of odd cheapo meters i keep for things like working on the car, etc...
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