Sears Roadtalker 'slant face' SSB receive roll off issue

[doffo]

Hello,

I managed to bring the radio back to being able to receive/transmit. It does good on power. The issue that is happening is that in either SSB Mode, the signal will eventually "roll off" till no signal comes in.... The second you transmit and the relay clicks, it comes roaring back. From what I gathered, I don't think the relay is at fault. Once you switch to AM, its working just fine and the receive comes back. Its just the second you switch to either LSB or USB, it instantly goes away up until you transmit and let go, then the receive comes back for a random amount of time. It seems the longer you do transmit, the longer the receive will stay until it slowly goes away. Once the receive is gone, and if you are quick on the PTT on the mic, you can hear it barely come up and it goes away immediately.

Aside old capacitors, what other parts may make the radio behave this way?

Thanks a ton for all the help so far on the other radios.

 

[BC Coyote]

Gotta say it....likely an old electrolytic cap somewhere in the SSB receive circuit.
I guess it could also be something heat related like a voltage regulator that works when cold but fails when it heats up, or a cold solder joint somewhere; those can create all kinds of weird symptoms......

And I'll now defer to those who know more than I !

 

[doffo]

Gotta say it....likely an old electrolytic cap somewhere in the SSB receive circuit.
I guess it could also be something heat related like a voltage regulator that works when cold but fails when it heats up, or a cold solder joint somewhere; those can create all kinds of weird symptoms......

And I'll now defer to those who know more than I !

I hear ya. I just have better condition slant face Sears Roadtalker radios I would rather recap vs this one. Was fun undoing the butchering and at least got it to go again, but thats when I found out about the receive on SSB slowly rolling away. I can get it to go out quicker if I turn down the RF gain. Otherwise, switch back to AM and it comes roaring back to life.

 

[nomadradio]

A look at the schematic for a SSB CB usually reveals a capacitor or two that is switched into the AGC circuit for sideband mode and switched out for AM. The automatic gain should respond quickly in AM mode, but more slowly for sideband, and that's why extra capacitance gets added to the AGC circuit in those modes.

Sounds backwards, though. Old caps tend to lose capacitance. This would make it recover faster, not slower. Makes me wonder if the mode selector has an oxidized contact or two that isn't completing every circuit when you change modes.

Maybe. Still sounds like the reverse of the symptom I would associate with a failed cap in the gain-control circuit.

73

 

[doffo]

A look at the schematic for a SSB CB usually reveals a capacitor or two that is switched into the AGC circuit for sideband mode and switched out for AM. The automatic gain should respond quickly in AM mode, but more slowly for sideband, and that's why extra capacitance gets added to the AGC circuit in those modes.

Sounds backwards, though. Old caps tend to lose capacitance. This would make it recover faster, not slower. Makes me wonder if the mode selector has an oxidized contact or two that isn't completing every circuit when you change modes.

Maybe. Still sounds like the reverse of the symptom I would associate with a failed cap in the gain-control circuit.

73

Appreciate the information. Maybe for another time I will sit down and recap the radio. But I do have nicer ones that I would want to recap first that work. Least it will be something to make note of and shelf the radio for the time being. This Roadtalker went from a dead state to at least being able to transmit fine in all modes. Had to undo the toggle switches and the goofy home-made roger beep board inside and bridge back the traces to where they once were.

 

[doffo]

Makes me wonder if the mode selector has an oxidized contact or two that isn't completing every circuit when you change modes.

..... Funny you mention this....

Brought out my other Sears Roadtalker 40 channel SSB radio, their first one with the flat face and big channel knob, and AM and USB was only working. LSB was dead on both receive and transmit. Gave the selector a good few jiggles left to right and it sprung to life lol.... Damn oxidized contacts will get ya.... So with my other Roadtalkers I need to give the selector a good cleaning as well as everything else.