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

"Telstar Electronics" wrote in message
oups.com...
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...

You don't think it might be caused by him not having at least 9 square feet
of ground plane?



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Thanks...........that sounds super. I have the radio apart on my bench
downstairs. Gosh........what a brick! Isn't is great, when you have to undo
everything that the "technician" did to upgrade the radio?
There were several other problems that I have found. Why the manufacturer
chose to use hot glue on all of the solder lugs of the switches escapes me.
This caused several solder connections to fatigue and break off.
It looks like this repair will be an hour here and there. I might get it
fixed in a few months. The one redeeming quality is the great Rx section.

Pete

"Telstar Electronics" wrote in message
oups.com...
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

Well, I have replaced a few of the electrolytic caps in the modulator
section, and I have SSB audio. Now, on to the AM section.............

"Pete KE9OA" wrote in message
. ..
Thanks...........that sounds super. I have the radio apart on my bench
downstairs. Gosh........what a brick! Isn't is great, when you have to
undo everything that the "technician" did to upgrade the radio?
There were several other problems that I have found. Why the manufacturer
chose to use hot glue on all of the solder lugs of the switches escapes
me. This caused several solder connections to fatigue and break off.
It looks like this repair will be an hour here and there. I might get it
fixed in a few months. The one redeeming quality is the great Rx section.

Pete

"Telstar Electronics" wrote in message
oups.com...
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