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Low volume PC76XL Philippines

1jonnyz

1jonnyz

Member
Dec 30, 2011
62
3
18
I am messing around with this radio and I hear nothing if I have my NB in any position but off, with it off I get low voume. I tried it with an external speaker and it is low volume also, unless I have the NB on and then nothing. I tried it on PA and it is LOUD! Any idea where the problem might be? Thanks! Jon
 

I should clarify... when I say it was loud in PA mode, that was with the mike keyed, when mike is not keyed it is low volume.
 
If the mic isn't the problem, I would look for shorted wires, or solder bridge, at the mic jack, the pa/cb switch. Maybe look at the audio chip (ic4), the tx switch (tr21). May be labeled different on a uniden, those are cobra 29 labels. Look at the pa/external speaker jacks, maybe someone hacked up a talk-back mod.
If ya figure it out, I'd be interested to know what it was...good luck
 
If the radio hasn't been messed with internally; then it is purely a mic problem.

If it has been messed with inside; then it could be a number of things.

I would go over the mic and exhaust that possibility - first . . .
 
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OK, I found Q7 was very leaky, I changed it to a 2sc2999 and put in schottky diodes in place of D4, 6, and 7. I tested the caps around the audio chip but they were all good, looks like someone replaced them.

When I fired it up I had static with the radio on and the NB off, much louder than before. I still heard nothing with the NB or ANL on. I decided to align the receive using my HP 8656B and Kikusui scope. I followed the alignment instructions for a Cobra 29. I tried to use my VTVM but could get no reading.

AFTER the alignment I now here NO static in ANY NB position. I could hear the signal generator at 6 uV but no static at all. I have a Grant XL and a Connex 3300HP-ZX and both of them I could hear static plus the 1kHz tone down to 1 uV. Any ideas where to go from here?
 
1jonnyz said:
OK, I found Q7 was very leaky, I changed it to a 2sc2999 and put in schottky diodes in place of D4, 6, and 7. I tested the caps around the audio chip but they were all good, looks like someone replaced them.

When I fired it up I had static with the radio on and the NB off, much louder than before. I still heard nothing with the NB or ANL on. I decided to align the receive using my HP 8656B and Kikusui scope. I followed the alignment instructions for a Cobra 29. I tried to use my VTVM but could get no reading.

AFTER the alignment I now here NO static in ANY NB position. I could hear the signal generator at 6 uV but no static at all. I have a Grant XL and a Connex 3300HP-ZX and both of them I could hear static plus the 1kHz tone down to 1 uV. Any ideas where to go from here?
Click to expand...
If you can hear the signal at 6uV but not until that much; then there is something wrong in one of the receive gain stages after the 2999. Perhaps check the receive diodes (don't recall their numbers; it is on the schematic - tho).

How mangled was this radio when you got it?
 

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