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My son bought this USB microphone for his computer. It only works if you keep your hand on the volume knob. I assume this is a grounding problem. I took it apart. It looks like the copper wire attached to the housing is there for grounding - it attaches near the rear of the volume knob. But touching that wire or touching any part of the interior of the knob does nothing to get the sound to work; only the front of the knob makes the sound come through. What can I connect to what to get it to work without having to put a finger on this thing? Thanks!

enter image description here

enter image description here

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  • \$\begingroup\$ I have the same mic doing the same thing. Fifine has not responded to my inquiries so I went looking for answers. Did you ever get your repaired after the lesson learned above? \$\endgroup\$ – Matt B Feb 16 at 21:58
  • \$\begingroup\$ Matt B - Welcome :-) However site rules mean you shouldn't ask clarification questions in the "Your Answer" box, as this isn't an answer & so it may be deleted (subject to moderator discretion). See the tour and help center to read more about Stack Exchange sites and how they are different to typical internet forums. When you have enough "reputation" you will be able to post comments, which is how clarification questions can be asked. See here for more details: "Why do I need 50 reputation to comment? What can I do instead?". Thanks. \$\endgroup\$ – SamGibson Feb 16 at 22:05
  • \$\begingroup\$ This does not really answer the question. If you have a different question, you can ask it by clicking Ask Question. You can also add a bounty to draw more attention to this question once you have enough reputation. - From Review \$\endgroup\$ – winny Feb 17 at 8:20
  • \$\begingroup\$ MattB REad bobflux's answer and the OP's comment re contact pressure - and Tony et al's comments re WD40 \$\endgroup\$ – Russell McMahon Feb 17 at 13:52
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If it is a grounding issue, touching it could change the amount of hum, buzz or interference.

However you say "It only works if you keep your hand on the volume knob" which I interpret as "there is sound only when the hand is on the volume knob, otherwise there is no sound."

If this is the case, then I'd suspect a bad contact perhaps at the pot wiper, or a cold/broken solder joint that makes contact only when the volume pot is messed with.

You can check this by touching the volume pot with a non-conductive object like a plastic rod. You can use the shell of a ball point pen, or a toothpick for example. If wiggling the knob around with a non-conductive object results in the sound turning abruptly on or off, then you can rule out any influence from your conductive finger, it'll probably be a bad contact.

If the failing contact is at the pot wiper, it will depend on the pot's position. So if the problem does not depend on the pot's setting, it is more likely this is a bad solder joint on the board.

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    \$\begingroup\$ Thank you - you were correct that non-conducting pressure works. \$\endgroup\$ – Jim Hunziker May 16 '20 at 19:36
  • \$\begingroup\$ Use electronic spray or WD40 drops only \$\endgroup\$ – Tony Stewart EE75 May 16 '20 at 22:26
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Repair questions are off-topic on this site so let's make it an education question.

enter image description here

Figure 1. Potentiometer terminals 1, 2 and 3.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 2. A schematic showing the potentiometer arrangement. As the wiper (2) is adjusted from (1) to (3) the volume goes from zero to maximum.

If pressing on the potentiometer causes the system to work then it's possible that the wiper has lost contact with the resistance track. You can test this safely by turning the knob to mid-position and connecting (2) to (3) with the tip of a screwdriver. If that works the potentiometer is faulty.

If you're feeling brave you can desolder the potentiometer, bend the tabs folded underneath and disassemble. You might then be able to bend the wiper a touch so that it springs onto the resistance track more firmly. A spray with some contact cleaner would be good if you have access to it.

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  • \$\begingroup\$ Thanks for the suggestion. @peufeu's suggestion to try non-conducting pressure to rule out grounding confirmed your guess. \$\endgroup\$ – Jim Hunziker May 16 '20 at 19:37
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The First Photo "looks" like it's broken...

But assuming it's not, this behaviour looks like the potentiometer (variable resistor) is broken. The pressure of the finger pushes the wiper contact on to the track completing the circuit.

It's also possible the solder joints are "dry" and need to be reflowed

Otherwise replace the potentiometer or the whole device would be the best advice.

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