I purchased a set of dual comm Peltors from an e-bay vendor that had sold several sets to friends of mine. Everyone's worked. Mine worked. And then, the right side headphone started toning at high pitch whenever turned on. The pitch would modulate relative to the amplification--ie it got louder when you cycled the volume higher and softer when the volume was lowered.
First things first, I changed to fresh batteries. I have disconnected the boom mic, which had no effect.
Pulling them apart, it appears that the battery contacts on the right headphone (the one with the tone) show significant corrosion on the negative contact. This is easily fixed, but for the fact that the contacts are heavily potted with a translucent epoxy. The same side headphone showed what appeared to be potting material soaked onto the foam inner cover, centered around the active microphone (the one that listens to the world around you and amplifies ambient sound). Between the battery contacts and the brown potting material/corrosion around the active microphone, I am leaning towards the active mic being blown. What is odd is that when I tap on the active mic, the tone will disappear for a moment...
It should be noted that the main control board for Comtacs (be they single, dual, or no comms) is in the left side headphone. I pulled apart that side, and checked both headphones for obviously corroded, broken, or faulty connections, but found none.
So, my questions are these: have any of you run into a problem like this in the past (a high pitched tone that modulates with volume settings)? Given the behaviors listed, am I way off base in my diagnosis? Does anyone have a schematic and/or parts list for these things?
If I can get a parts list, I can just order a new active mic, solder it in, and see what's what...
PS: it's $230 to send it back to 3M for repairs, given that I don't have the original sales receipt, so I can afford to spend some time and money on this one.
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