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Cleaning pots in old analog meters

Discussion in 'General Electronics Discussion' started by guitar1580, Jul 22, 2014.

  1. guitar1580

    guitar1580

    4
    0
    Jul 22, 2014
    I have a couple of old Triplett 310 VOMs, and a couple of old Simpson 260 meters. I mostly use the small Triplett, because it's more handy, and fits in my toolbox. The last time I used it, I noticed the needle jumping around when I zero the resistance scales. I've eliminated the leads as the cause. My one Simpson does the same thing.

    I haven't had the Simpson apart in a while, but I noticed the zero adjusting pot on the Triplett 310 is in plain view when I take the back off. I was wondering if anyone has any suggestions for cleaning the pots on these meters. I have some Deoxit spray cleaner, and lube, that I use on stereo receiver pots, and I would think it is safe to use on the meter pots, and selector switch. Any advice would be appreciated. I'd like to clean up the connections without sending them back to the factory.

    JT
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    I would check for corrosion on the battery holder and battery contacts, and dry joints on the circuit board. Also check that the sockets for the meter probes are clean and tight.

    Clean the selector switch contacts with isopropyl alcohol and a cotton swab. Clean both the stationary and moving parts thoroughly, but be very gentle with any flimsy springy metal as it's easy to bend it.

    If that doesn't fix it, upload some photos of the meter, both sides of the board, and close-ups of the zero-ohm potentiometer.
     
  3. shrtrnd

    shrtrnd

    3,665
    453
    Jan 15, 2010
    If you spray contact cleaner into the pots, run the pot up and down full scale several times so the wiper can try to clear the carbon debris from the resistor wafer.
    That usually works unless the resistive element or wiper within the pot is excessively worn.
     
  4. guitar1580

    guitar1580

    4
    0
    Jul 22, 2014
    Thanks guys. In the Tripletts, I cleaned the battery & fuse connections, and cleaned the selector switch contacts with alcohol, and it seemed to solve the problem, so I didn't spray the pot.
    A lot of black dust came off of the switch contacts. Now the switches feel a little dry. I have the Deoxit Gold (G5), which I believe is more of a lube to be used after the Deoxit Cleaner (D5). Does anyone recommend using the Gold on the switch contacts to make it more smooth, or will this attract dust?
    Also, does anyone know the best way to tighten up the Triplett 310 leads where they plug in? One set goes in fairly tight, the others drop in a little loosely.
    Thanks again for the input.

    JT
     
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