I'm kind of new to electronics and sorry if this is a bad question.

I am trying to repair my father's old radio transmitter and I noticed that the PTT won't pick up your voice. I opened it up and found that in the microphone there is a ceramic capacitor that is burned. It is a 101 but I only have a 56, a 104 and a 220 at hand.

Can I replace the burned one with one of those mentioned without breaking the PTT?

enter image description here

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    \$\begingroup\$ I doubt that capacitor is bad, it may be stained but not burnt. The mic would work without it. So if you really believe it is bad, just remove it. \$\endgroup\$ – lakeweb Jul 18 '20 at 0:53
  • \$\begingroup\$ it is with a black stain in both sides but as you say, im going to try removing it thaks for the reply! \$\endgroup\$ – Rigo_158 Jul 18 '20 at 0:57
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    \$\begingroup\$ Code 101 is only 100 pF. Normally used to help audio circuits ignore local RF noise, and reduce the hiss of ancient transistors. \$\endgroup\$ – user105652 Jul 18 '20 at 0:57
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    \$\begingroup\$ After you remove it, put an ohm meter to it. I'm sure it is not shorted. \$\endgroup\$ – lakeweb Jul 18 '20 at 1:00
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    \$\begingroup\$ it;s there to prevent the radios microphone from picking up the radios transmissions 56 should work almost as well the others are all too far out of range. \$\endgroup\$ – Jasen Jul 18 '20 at 3:41

If you must replace that capacitor, then you should use the 56 pF part rather than one of the others you have at hand.

The part you are looking at is a 100pF capacitor intended to "short circuit" any of the transmitted radio signal that might find its way to the microphone. If you use one of your larger capacitors, it will "short circuit" the lower frequency audio signals produced by the microphone - your microphone signal will be weakened, and your voice will sound really quiet to whoever hears your transmitted signal. If you use a capacitor that is too large, there will be no audio from the microphone at all.

Regardless, I don't think you need to replace that capacitor at all.

There's no voltage source in that microphone capable of delivering enough voltage and current to damage a ceramic capacitor. If an external voltage source capable of destroying that capacitor had been connected to the microphone, then much more would have been damaged than just that one capacitor - you would see burned and exploded components all over the place.

Ceramic capacitors don't "go bad." They are ceramic (like a dinner plate.) Some other types of capacitors (oil and paper or electrolytic capacitors) have liquids in them and they go bad over time because the liquid dries out or leaks out. Ceramic capacitors have no liquid so they don't go bad over time.

Ceramic capacitors can break, but then you'd see that. They are some what fragile and sometimes split or fall apart from physical movement. That would be obvious though - you would see cracks or visible crumbling of the part. Your capacitor looks fine.

The microphone will normally work fine without the capacitor if you keep the microphone away from the antenna and the antenna cable.

Remove the capacitor, try out your microphone. If it still doesn't work it wasn't the capacitor.

  • \$\begingroup\$ thanks a lot for the info, i removed the capacitor and it worked but when i transmit the is a kinda white noise on the backround, but it works!, i think i will have to put a new one on \$\endgroup\$ – Rigo_158 Jul 19 '20 at 2:24

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