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Pc76 audio chip

Dirty Duck said:
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.
Click to expand...
Ok, I think you said you only have a dmm and a dosy meter? If so, and a scope isn't available, this complicates the procedure, but I will try.

Using a dmm on the 10k resistance scale, probe pins 1 and 2 of the mic jack. Turn the mic gain knob back and forth, see if that reading goes from low to high, maybe 1 ohm to 5k ohms. If so, the mic audio is making it to the mic gain knob. If you get no resistance reading, you have found an issue. Maybe a wire came loose or the mic gain opened up. If you get a low resistance that doesn't go up, probably have a shorted cap or a short to ground right past the mic jack.
 
Dirty Duck said:
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.
Click to expand...
How much dead key are you seeing? At least it's switching to transmit, the led is changing to red, you have rx audio so your audio chip is probably fine. And the driver and final are making power, so the modulation transformer isn't open. If above resistance check is good, we may be looking at a capacitor issue, given the buzzing you hear. Btw, when transmitting, do you hear the buzzing on the uniden or the cobra?
 
Cable Guy said:
How much dead key are you seeing? At least it's switching to transmit, the led is changing to red, you have rx audio so your audio chip is probably fine. And the driver and final are making power, so the modulation transformer isn't open. If above resistance check is good, we may be looking at a capacitor issue, given the buzzing you hear. Btw, when transmitting, do you hear the buzzing on the uniden or the cobra?
Click to expand...
When it decides to transmit a “buzz” I’ll hear it on the cobra. I’m at work right now but, I’ll get on it as soon as I get home.
 
Cable Guy said:
Ok, I think you said you only have a dmm and a dosy meter? If so, and a scope isn't available, this complicates the procedure, but I will try.

Using a dmm on the 10k resistance scale, probe pins 1 and 2 of the mic jack. Turn the mic gain knob back and forth, see if that reading goes from low to high, maybe 1 ohm to 5k ohms. If so, the mic audio is making it to the mic gain knob. If you get no resistance reading, you have found an issue. Maybe a wire came loose or the mic gain opened up. If you get a low resistance that doesn't go up, probably have a shorted cap or a short to ground right past the mic jack.
Click to expand...
I will as soon as I find my tester again. Looks like I currently dead key 1 watt
 
Cable Guy said:
Using a dmm on the 10k resistance scale, probe pins 1 and 2 of the mic jack. Turn the mic gain knob back and forth, see if that reading goes from low to high, maybe 1 ohm to 5k ohms. If so, the mic audio is making it to the mic gain knob. If you get no resistance reading, you have found an issue. Maybe a wire came loose or the mic gain opened up. If you get a low resistance that doesn't go up, probably have a shorted cap or a short to ground right past the mic jack.
Click to expand...
 
Ok currently with radio both on and off 1 and 2 do not register.

My mistake because I didn’t see on of my probs touching the outer ring.
 
Ok, you should see close to 0 ohms with mic gain down, about 5000 ohms with mic gain up. I'd leave the radio off for those measurements. If you say it doesn't register, does it say OL, or open, what does the meter say? A few pics would be helpful.
 
IMG_3653.jpegOk this was all on minimal modulation without turning the knob. It wanders from as you see 2-280.

I didn’t get a photo of maximum modulation but, it was stuck at 1.

I then turned the modulation back down and it started wandering again on minimum.

I’m calling it a night because I’m beyond confused now.
 
So, 2 ohms all the way down, and I guess 1 ohm all the way up. That's not right. When you feel up to it, take some pics of the inside of the radio, like these....

Behind the mic connector. Red, yellow, blue and white wires.
17557419160415950525905287412689.jpg

Board directly behind the mic connector. You can see where those mic wires go. You can grab them individually and lightly tug to see where they go. Make sure they're all connected.
17557419971744397660566088081294.jpg

Directly behind the mic jack, Solder side of board, where the wires connect from the mic jack. To see if the traces are burned or a cold solder joint, anything not right.
17557423213929202826607312864292.jpg

The modulation pot and limiter, center rear of the board, next to the modulation transformer (green wrapped here, yours may be different color).
17557420544206306935615935498267.jpg
You can see that D11 is clipped on this radio, that disables the limiter and it will be fixed soon, but I need to see these of your radio.


General solder side of the board. Get this as clear as possible.
17557427182155040185675801535565.jpg
If your readings are right, mic audio is shorted to ground somewhere. Could be the yellow wire came loose and touching something. Could be a failed attempt at defeating the limiter. Could be any number of things, but the pics will help us help you.
 

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