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Cobra 142GTL with no AM receive or transmit. BUT has SSB transmit

Frylock508

Member
Jul 25, 2011
28
1
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Hi Everyone, I have a Cobra 142 that was gifted me by a good friend who picked it up off eBay. Worked great for a couple of weeks and then stopped transmitting & receiving on AM. Here's a little backround on the radio. Its been heavily modded for audio,wattage, and channels have been done. A potentiometer has been installed to drop it down to 1 watt and to dead key around 5 and swinging to around 18. The channels are done in a way I'm not familair with. Hopefully someone on here can explain. Its all done through a 3 position swith next to the mic plug. On the back of the switch is 3 crystals. We tracked it to go about 44 up and 26 or so down with some skips along the way. Never heard or seen this mod before. My original radio had 26.815 to 28.045. A standard I thought. ANYWAY, I have seen people post that this is a common problem and to change the 2SC1419. Located in the back right side of the radio. MY RADIO HAD A DIFFERENT ONE AND LOOKED LIKE IT WAS CHANGED FAIRLY RECENT. MY final has 331 marking on it. Same size as whats supposed to be in there but mine has the 331 on it with "N2" above it. I have not been able to cross reference this with any transistor. ANYWHERE!
So I swapped it out with a C1419 from a Cobra 2000. Still no good. Plus, the guy who did the last swap put so much solder on the leeds that it smeared AFTER I had no results from the initial install. The smearing occured after I got no results and wanted to make sure I had a nice weld. Now I have to copper braid the mess before I proceed. ANY HELP WOULD BE GREATLY APPRECIATED. You guys have saved my a$$ in the past and hope you can again. Thank you
 

If this radio is important to you; then perhaps it is time to send out to a reputable shop and have it sorted out and set right.

I have a 142 that was given to me, and went through it and set it back to stock after fixing many similar problems. Gave it an alignment and also peaked the TX coils; it works as well on AM as it does on SSB. I would suggest the same . . .
 
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Unfortunately any reputable radio shop we had in my area went out of business soon after the Ranger 2950's started coming out in the early/mid 90's and people were able to do their own mods. Now thanks to forums like this and others people are able to do most anything. That's why I am hoping someone has gone beyond just replacing the final on this radio and has found another component for me to go through. Thank you for your response though.
 
after reading your post it says AM stopped working and you changed a 331 to a 1419. then you mentioned the final. the 1419 is not a final it is a AM regulator for AM. not a final. do you have TX and RX on SSB?
we need good info here to help you. do not worry about the channel board for now. just let us know what works and what does not. does the 142 have pa fubction on it?do you have equipment to check for voltages and a freq counter and a way to inject a tone into the radio. does the s meter move as if it is recieving ,does the tx and rx light change. does the s meter move when you key the radio etc.
 
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Thank you for responding, Sonoma. The Tx and Rx change when keyed in ssb.
There is also receive in ssb. As soon as I turn it to AM it stops lighting up TX and you hear nothing. This radio does have a cb/pa switch that I believe was disabled for a channel mod and never connected again. We had an ice storm here one morning before i went to work so I checked my SWR's before leaving. They were fine. I get home later that evening and this problem starts happening. I will confirm that the PA is indeed disabled being that nothing happened when turning it on and off in the past. The S meter is working as well as the mod/swr meter. But in ssb only. I do have equipment to check for voltages as well as frequency. Again, I appreciate your help.
 
OK you are saying SSB receives and transmits. is this correct. if so the final is good. you have another problem since the TX light does not come on when you key the radio. there could be a capacitor or a transistor bad some where in the switching circuit. can you verify the am to ssb switch is working properly. you need to make sure you are getting 8 volts at the switch in AM mode. since SSB is working it will have 8 volts to it. it could even be a bad switch not turning on AM.
 
Update: So after checking the voltage at the switch I tried to key the radio into a dummy load. It keyed and the RX light came on. BUT no modulation on the meter. So I then put the radio inline to see what was really happening. When keyed in AM mode its making a hum and swinging it to full wattage. I'm unable to turn the dynamic control down or anything. Its pinning the S/RF meter in AM. SSB is uncopyable. Still no receive in AM even though its transmitting a signal. So I'm guessing this could have been the problem even before I replaced C1419. A bad contact perhaps?
 
most of the time the way you say the radio is acting is the 2sc1419 is shorted. make sure the voltages are right on it.
 

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