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I have an old AT&T Tel. answering device that I would like to keep going as long as possible. However, the volume pot is absolutely shot after trying to service/clean many times. I haven't been able to find a replacement pot so I would be delighted to just have the volume "loud" if possible leaving the bad pot in place. Is there a way to by-pass it? Perhaps with a jumper? If so, how should it be done? I have included 2 photos of the double-sided circuit board with descriptive comments for reference. The third photo is of the actual speaker.

Photo 1 - Top-side of board showing pot (black rectangle) Top-side of board showing pot (black rectangle)

Photo 2 - Underside of board with outline of pot position Underside of board with outline of pot position

Note that the posts are numbered 1,2,3,4 consistently on each side.

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    \$\begingroup\$ It looks like pin 4 is not connected, so you have a normal three-terminal pot. I might guess that terminals 1 and 3 are the ends of the resistance element, and 2 is the wiper. This could be confirmed with ohmmeter measurements. \$\endgroup\$ Jun 23, 2016 at 3:48
  • \$\begingroup\$ I suspect the wiper is internally shorted to one end . Thereby changing the volume of both microphone and earpiece. A schematic would be helpful. \$\endgroup\$
    – Old_Fossil
    Jun 23, 2016 at 4:04

2 Answers 2

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It could be a conventional stereo pot (old style circa 1970's) - check out surplus stores or Amateur Radio flea markets (Hamfests as they're called). Probably cost a quarter or two.. Do you know the resistance?.

EDIT: The type of pot a volume control is logarithmic pot as opposed to a linear or non-linear pot.

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  • \$\begingroup\$ A stereo pot would have six terminals, not four. \$\endgroup\$
    – Transistor
    Jun 23, 2016 at 6:37
  • \$\begingroup\$ A linear would still do the job, but the scale is nothing-loud-very loud-very loud-very loud-very loud :-) \$\endgroup\$
    – winny
    Jun 23, 2016 at 8:00
  • \$\begingroup\$ @transistor: or two mono pots. \$\endgroup\$
    – Old_Fossil
    Jun 23, 2016 at 21:20
  • \$\begingroup\$ Can you explain further? (1) A potentiometer has three terminals. It would be possible to share the GND pins reducing to five but the signals and wipers require separate pins so that leaves 5. (2) The telephone system is monaural so a stereo answerphone is unlikely. (3) There is no connection to terminal 4. \$\endgroup\$
    – Transistor
    Jun 23, 2016 at 21:32
  • \$\begingroup\$ @transistor: It just looked like something I used to see years ago. I was checking on line for circuit diagrams for old phones and it seems you are correct....the question remains which terminal does what... \$\endgroup\$
    – Old_Fossil
    Jun 23, 2016 at 21:58
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It appears to be a monaural (1-section) pot. The connections look like...

  1. Top of resistance range. The signal goes INTO the pot here
  2. This is very likely the "wiper". The signal comes OUT of the pot here.
  3. This looks like the bottom of the resistance range. Likely common ground.
  4. No electrical connection. Provided for mechanical stability only.

I would move the pot to the top of the range ("volume loudest"), and connect pin 1 over to pin 2.

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