Cobra 29 ltd Chrome No tx audio

[Harley3315]

Have this on the bench with the tda2003 audio chip I have rx audio just fine no tx audio at all.
Not even the pa shows any tx audio any ideas? Half burned out audio chip I think they run the tda2003 in bridge mode
could half be tx half rx?

 

[OldTech03]

If you have an audio signal tracer or scope, follow the yellow brick audio road back to the TDA2003 you should be able to go from the Dynamike control and trace back to the mic preamp and see an audio signal on the scope or like i said an inexpensive audio signal tracer. Schematics are helpful in this if you have little experience with the 29's circuit layout.

 

[Harley3315]

If you have an audio signal tracer or scope, follow the yellow brick audio road back to the TDA2003 you should be able to go from the Dynamike control and trace back to the mic preamp and see an audio signal on the scope or like i said an inexpensive audio signal tracer. Schematics are helpful in this if you have little experience with the 29's circuit layout.

Well I think I have Schematics for the older 29's somewhere but not this newer style with tda2030 any idea what transistor acts as the mic preamplifier?

 

[nomadradio]

Umm, tried another mike yet.

Or trying this mike on a working radio?

Mikes tend to break sooner than radios, all other things being equal.

If the receiver audio is good with the volume turned up, the problem is not in the audio power-amp chip.

This would leave the mike gain control, and a one-transistor mike amp circuit to check next.

Do you have another radio on hand to monitor this radio's transmit audio?

73

 

[Harley3315]

Umm, tried another mike yet.

Or trying this mike on a working radio?

Mikes tend to break sooner than radios, all other things being equal.

If the receiver audio is good with the volume turned up, the problem is not in the audio power-amp chip.

This would leave the mike gain control, and a one-transistor mike amp circuit to check next.

Do you have another radio on hand to monitor this radio's transmit audio?

73

New mic was tried this is the one I use on the bench all the time works fine on my radio. changed the chip changed tr17 supposedly the mic amp and the 10 volt cap next to it for good measure nada still for tx audio or pa audio.

 

[nomadradio]

Something in between the mike plug and 2030 chip is blocking the tracks. A very bright light and a magnifier on the rear of the mike jack and the wires leading from it may reveal a fault. Mike gain controls fail regularly. Turning the mike gain to max, and then bridging across the wiper (center) lug and the clockwise lug with the tip of a screwdriver will bring back the mike audio if this is the cause. Naturally the other end of wires attached to that control are on the list of possible suspects.

Using PA mode with a speaker plugged into the PA jack sounds easier than using transmit mode. Once you have PA audio again, I predict the transmit modulation will come right back as well.

73