QCX+ audio attenuation 5 seconds after power on
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Sorry. Didn¡¯t see your name in the note. The symptoms you¡¯re describing sound like a dry solder joint. At least that¡¯s a good starting point assumption. Before looking for that I like to check the DC voltages on the op amps. Specifically you want to see about 2.5v on pins 1,2,3,5,6&7 of ICs 5,6,7&8. Also 2.5v on pins 5,6&7 of IC9, 4.9v on pins 1,2&3 of IC9 and a little less than half the input supply voltage on pins 1,2,3,5,6&7 of IC10. Please look at those voltages first and let us know what you see. That may point to a specific area to look at for solder troubles or whatever.? 73¡¸é´Ç²Ô On Fri, May 31, 2024 at 09:56 Cam via <camd1776=[email protected]> wrote: Hey all, I've had my QCX+ collecting dust for a few years.? When it was shelved, everything was working fine (according to a much more knowledge ham than myself - he had to fix a small assembly issue).? My son decided he wanted to learn CW so we've dusted it off and have been practicing a bit.? The first few days, after powering the unit on it would somewhat randomly reduce the volume almost completely.? We'd turn the volume all the way up on the radio and the speaker and could barely hear the dits and dahs.? After a minute or two, the volume would slowly return to normal (and we'd reduce the volume on the radio and the speaker).? It started to get worse, and now it's to the point where after about 5 seconds preceding power on the volume dies almost completely and never comes back.? If there is a transmission on frequency after power on it sounds beautiful, for about 5 seconds.? This occurs with or without an antenna connection (we are careful to put it into practice mode without an antenna) as well as with a dummy load.? It happens with an external speaker as well as with normal ear buds.? It happens on battery or on mains, but when on mains there's the added nuisance of odd high-pitched chirping as the volume is decreased to almost nothing.?? |
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Hi Cam. Well, it's possible that IC10 is internally shorted but also possible a problem in the voltage divider made of R39 and R40 along with C24 is feeding the wrong bias into the chip to start with. If the ground side of R39 was not grounded or "grounded" through a high resistance connection, a higher voltage would appear on pin 5, and would cause high voltage to appear on the other 5 pins. So check around that area first before removing IC10. But I think you're?in the right area... Good luck ... 73 .. .Ron On Fri, May 31, 2024 at 1:18?PM Cam via <camd1776=[email protected]> wrote: Thanks Ron!? Missed your message before I posted my last bit but it sounds like I might be on the right track now eh?? Think I should resolder those pins, or based on the high voltages just attempt to replace it? |
Ronald Taylor