The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

I have a cobra 139 xlr base, 858pll, pc- 176ab, no receive, no transmit, and the relay is not working. no movement on the meter. i put finals in the radio. i saw that the wires were off the cb/pa switch. someone put channels in the and used the cb/pa switch. and left all the wires tied up with tape. I was looking at another radio to put the wires back. when i was touching the wires I lost receive. I must have shorted out something in the radio, what part i short out. I appreciated if someone can please help me with this radio. thank you galaxy

This radio has turned into a real "Chicken or Egg" situation.

Even a sharp, experienced tech needs to put the wires where they belong FIRST to make measurements and identify what part of the radio has been shut down.

Or, if you could point to a radio with all the wires in place, and identify exactly which wire touched exactly what, you could trace back on the schematic and make a prediction about what part or parts that this could have overloaded and damaged.

Still leaves you needing to take a 'scope and/or meter, the schematic and start with each sectoin of the power supply, identifying who is alive and who is dead, one by one

Not too different from taking the plug wires off each spark plug in a Jaguar V-12, and then putting them back in random combinations to see if you can get it to run again.

And if one of those combinations causes a loud "CLUNK" from inside the motor when you try to start it, then ask the mechanic what got damaged.

He won't know from that description alone, no matter how good a mechanic he is.

73

thank you for your reply. ALL WIRES ARE BACK TO STOCK. GALAXY

Can you read and follow a schematic diagram?

If yes, check all CB/PA switch connects and verify that they are working when switching from CB to PA, next check for open circuit components at the end of the switch wiring to PCB. Try to give a better expiation of the faults you have (not just no audio) tell us thinks like, TX good with audio SSB and AM, S/RF meter shows incoming signal, and so no, as this makes it easier to find the fault. You may think you just have one fault but you may have other which are related, that why its best to give as much information as possible.

Rick

the radio does light up. there is no movement on the meter.there is no hissing sound coming from speaker. when i key the mike the relay is not working. no sound ssb. thank you, galaxy

Check D25 cathode or the end with black or white line for 7 to 8 volts, let us know what voltage you have.

Check D27 cathode or the end with black or white line for 13 to 14 volts (this is by the relay), let us know what voltage you have.

Check D28 cathode or the end with black or white line for 8 to 9 volts, let us know what voltage you have.

Check pin 1 of the audio amp IC4 for 13 to 14 volts, let us know what voltage you have.

Can you read and follow a schematic diagram?
I ask you the above question but you did not answer.

Rick.

checked d-25 it reads 7 volts,,d-27 it reads 14 volts,, d-28 its reads 8 volts. check pin 1 . it reads 14.62.. i can not read a schematic, thats why i need your help..... galaxy

hi there,just my two cents worth,but sounds to me like your in p.a. mode

All the voltages you have given us are correct the fault must be with the CB/PA switch or its wiring, which as already been suggested to you.

Rick.