Pc76 audio chip

[Dirty Duck]

I have an old Philippine Uniden pc76xlw with no audio at all.

I’m thinking I need to get an audio chip. I can’t tell which one it is.

Anybody know which one is needed?

 

[Dirty Duck]

quick update it’s From 1994 apparently.

 

[Cable Guy]

That's a big step, did you verify the mic is good? Also, the ext speaker jack has a switch in it to disconnect the internal speaker when you plug into it. That switch is known to corroded or tarnish, leaving no speaker audio, even if you never plug into it. I would try an external speaker first, and a different mic. Also, the internal speaker could be bad. Just saying, I wouldn't jump on the audio chip so quick, since most of the time it is innocent.

 

[Dirty Duck]

That's a big step, did you verify the mic is good? Also, the ext speaker jack has a switch in it to disconnect the internal speaker when you plug into it. That switch is known to corroded or tarnish, leaving no speaker audio, even if you never plug into it. I would try an external speaker first, and a different mic. Also, the internal speaker could be bad. Just saying, I wouldn't jump on the audio chip so quick, since most of the time it is innocent.

Yeah I got a good mic on it. I have the external speaker on. I still get the “pop” when the radio powers on.

Last I checked it was still transmitting.

This is my first radio I’m trying to fix myself with minimal tools and just a dosy meter.

Gotta learn some how.

 

[Cable Guy]

Ok. Try putting the radio in pa mode and plug the speaker into the pa jack. Can you hear anything? If you key the mic and talk, do you hear yourself?

 

[Cable Guy]

It probably has the TA7222AP audio chip, 10 pins, along the right side of the chassis from the bottom side (speaker side). I would start with a voltage check of those pins. The radio is old enough, could have a faulty capacitor. Use the service manual for the cobra 29 ltd on www.cbtricks.org.

Cobra 29LTD ST, 29WX ST

 

[Dirty Duck]

Ok. Try putting the radio in pa mode and plug the speaker into the pa jack. Can you hear anything? If you key the mic and talk, do you hear yourself?

Nothing at all

 

[Dirty Duck]

Another update, I was wrong on the transmit. When I key down I get a buzz.

 

[Cable Guy]

Also, when you take the covers off, on the solder side of the board, run your finger along the pins of the audio chip with the radio on and mic hooked up. If you hear hum, that's good.

 

[Dirty Duck]

Another update, I was wrong on the transmit. When I key down I get a buzz.

On top of that it isn’t consistent either. My voice isn’t heard.

I have a little cobra 36 st I use to hear myself with when I’m checking my audio

 

[Dirty Duck]

Also, when you take the covers off, on the solder side of the board, run your finger along the pins of the audio chip with the radio on and mic hooked up. If you hear hum, that's good.

Will do

 

[Dirty Duck]

It makes a hum-buzz just like you said.

 

[Dirty Duck]

Alright so the radio receives apparently as well.

Sorry for switching the diagnosis already.

So currently it receives and doesn’t transmit.

 

[Cable Guy]

It makes a hum-buzz just like you said.

Ok, just for starters I think your chip is okay. I will get back with you in the morning, it's bed time. Until then, with the radio unplugged, work the volume knob back and forth, completely, a hundred times, do the mic gain knob too. Then try it out. The pots get corroded and dirty if not stored right, and not used. It might help, but won't hurt if it don't. Does that mic work on the other cobra you have? Swap them out just for giggles.

 

[Dirty Duck]

Ok, just for starters I think your chip is okay. I will get back with you in the morning, it's bed time. Until then, with the radio unplugged, work the volume knob back and forth, completely, a hundred times, do the mic gain knob too. Then try it out. The pots get corroded and dirty if not stored right, and not used. It might help, but won't hurt if it don't. Does that mic work on the other cobra you have? Swap them out just for giggles.

The other cobra is a hand held. I got more mics hanging around.

Currently I have a dead key but, 0 swing and 0 modulation.

Probably a good idea doing this after some sleep. I’ll probably make a little more sense if I’m not as tired.

Thanks for giving me a hand.

I’ll turn the knobs and they are in fact dusty.