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Measuring Pots?


Charles218

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Is it possible to measure pots to confirm that they are working properly? Several times I've removed a pot, cleaned it, and then replaced it only to find that there was still a problem. It would be a real time saver if I could measure it so that I would know that it was functioning properly before installing it.

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Measuring the wiper to one of the sides of the pot may pick up some major problems. Using an older analog meter would help.

When I redid my AR-2AX's a couple of years ago, I hot-wired my pots to a junk speaker from my amplifer after cleaning them up. It gives you a good idea if there is still much of a noise problem.

I don't recall how exactly I did it. I think I just wired one side of the pot to the + of the amp and the wiper to the + speaker terminal. I then wired the - of the amp to the - of the speaker to complete the circuit. Run music through your amp, rotate the pot back and forth and listen for excessive noise or dropping out. Effectively you are just putting a variable resistor in series with the speaker.

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Tom H provides a good way to test a pot for basic functionality. However, if you truly want to measure a pot as you stated, you do need a DMM or analog multimeter. Clip the leads to the 1 and B tabs and rotate the stem and watch the meter for blips in a smooth response that should range from almost 0 ohms to 16 ohms.

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Tom H provides a good way to test a pot for basic functionality. However, if you truly want to measure a pot as you stated, you do need a DMM or analog multimeter. Clip the leads to the 1 and B tabs and rotate the stem and watch the meter for blips in a smooth response that should range from almost 0 ohms to 16 ohms.

No argument but IMHO an analog meter works much better as you rotate the stem. Digits tend to change rapidly while dips in a needle are easier (for me) to interpret.

Kent

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Thanks for the responses, I just knew that there must be an easier way than putting everything back together and doing a listening test. At least now I will have a sense of confidence that my pot cleaning job made a difference.

Kent, last summer I found a beautiful, vintage Triplett 640-PLK voltmeter. I really get a kick out of watching the needle elegantly move from side to side as I make measurements. I'll get it busy on the pots that I'm currently working on.

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  • 3 months later...

Yes, by connecting the leads on your ohm meter to the "B" post (the one in the center of the pot) and then to either the "1" or the "2" terminals, you ought be able to see the meter swing smoothly from 0 to around 15 ohms without any major fluctuations or drop outs as you turn the pot through its range of motion. If the meter is swinging nicely in one direction and then hops way up to a very high or an open circuit (infinite resistance) reading as you are turning the adjustment knob and then back to where one left off before the jump, that indicates that there is a dirty/corroded non-conductive patch on the nichrome wire. At that point there will be little or no signal going to the speaker and thus no music. Shoot for smooth and continuous. That leads to smooth and continuous music. :)

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  • 2 years later...

I have always used a DMM, but I can see the advantages of using a analog multimeter. If you change the lead from the 1 to the 2 terminal the range changes direction from 0-16 ohms to 16 to 0n ohms. Visual inspection of the wiper and the coil can tell you a lot, but only testing the true resistance can confirm correct operation. Smooth operation of the wiper throughout the range is what you want. Any bumps or sticky spots (I call these hiccups) usually indicate a problem.

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