Cobra 29ltd issues

[kaos513]

Hello guys here are the issues:
works: tx/rx light, key up red tx
what doesnt work: no key up power, no audio and faint receieve. thanks.

 

[nomadradio]

Any chance the power supply polarity got connected backwards?

Burned parts attached to the power socket will generally reveal when this has happened.

73

 

[kaos513]

i had opened it up cleaned it up,aligned the radio was working fine left the radio on bench for 3 days fired it up and nothing,

 

[sonoma]

you might look for a bad solder joint in the VCO,PLL, and audio IC areas. over the years I have seen so many radios with bad solder joints and ever dirty controls on the front of the radio.
had a lot of the Superstar 121 radios to come in with bad solder joints from some of their last production models. I have 2 right now with a dead issue like you are having and need to go over the solder joints. since they started acting up for the owners with a work no work problem. one the guy said he could turn the power switch on a few times and it would work for most of the day.

 

[Handy Andy]

No key up power signals no carrier...

Weak receiver - squelch on?

Or...

Was work done around the AM Xfrmr? Mod transformer (reactance Modulator)

Output of Chip to Cap - Cap failed?

Does the side where the Audio amp is, does it get hot around that Audio Amp chip?

May mean the Audio Amp chip or it's output cap is on it's way out...

If none of the above, try external speaker and also PA using the external speaker on the PA jack for audio test...Mic work? Hear full volume?

 

[kaos513]

Tr23 gets hot

 

[kaos513]

I had recapped theradio sometime ago , stopped working after it was on my bench for 1 week

 

[Handy Andy]

TR 23 is the main regulator - Do you have voltages on TR23? If two legs of it, go to zero, Stop! You have a short somewhere, save the TR23 if you can.

Restart your "Hey looks like a cap shorted" hunt, like at C114 and C119.

Check the branch off of TR23 - it even goes to the 5 VDC regulator for the PLL chip too...at C114

D21 can be suspect too, but you'd have strange results with that part...

 

[kaos513]

I solved it, some reason i had to do the alignment all over agian works now.

 

[kaos513]

I will keep any eye on the radio maybe there is a part failing.

 

[Shadetree Mechanic]

Gremlins.

 

[loosecannon]

i can't see how an alignment would cause TR23 to get hot.
My guess is that you set the radio down on the bench and TR23 or some other part on one of it's branches was touching some errant solder blob, cut off end of wire, or other "bench metal".

now that you've moved the radio around a bit, whatever it was shook loose.
LC

 

[Robb]

i can't see how an alignment would cause TR23 to get hot.
My guess is that you set the radio down on the bench and TR23 or some other part on one of it's branches was touching some errant solder blob, cut off end of wire, or other "bench metal".

now that you've moved the radio around a bit, whatever it was shook loose.
LC

Yeah, I agree LC.

KAOS: It's times like that that one needs to clean all of the solder joints on the bottom with an old tooth brush and some rubbing alcohol over an old newspaper and then rinse with clean alcohol. Then, examine all of the solder joints with a magnifying glass looking for incomplete solder joints, solder blobs, or solder joints that look dull grey after they have been cleaned.

Fixed more than a few radios doing just that w/o any other parts needed. Some radios are worse than others in that regard. Galaxies and RangerUSA made Cobras were the worst so far - IMO . . .YMMV . . .

 

[kaos513]

i did find some solder around c87 touching another ceramic cap cleaned it out.