On Feb 17, 1:59 am, "Pete KE9OA" wrote:
Another eBay special that "worked perfectly". It doesn't matter if I put in
an external audio source from an audio oscillator or a microphone. I've
tried three good microphones, and have the same problem. When I first key
the mic, Tx audio is fine, but it quickly, almost abruptly fades after about
2 seconds. Has anybody seen this problem?

Pete

It certainly could be many things... but what you describe would lead
me to replace the high power audio IC. I'm assuming that it has one...
and uses a high-level modulation scheme. I have seen these fail in the
way you have described. I believe what happens there is that the
internal die has somehow lost contact with the heat sink... and
therefor heats rapidly... sending semiconductors within the IC all
over the bias map. This IC is normally failrly cheap, available, and
is usually easy to replce. Hope that helps...

www.telstar-electronics.com