RoadTalker 40 Mobile probs

[Farmer Brown]

I've had this unit for 5-6 years and never hooked it up. So now that I've got around to it, it lights up and seems to have ears on some channels but others it has no static or anything.

Channels that it will key up on, the modulation light comes on in the meter swings. But I cannot hear nor can I be heard.

Could the channel selector just need cleaning or does this sound like the crystals are messed up? I do not have any experience with a radio with crystals.

Advice or suggestions are very much appreciated, as I would like to have this as my mobile radio.
Thanks, Farmer

 

[Shadetree Mechanic]

I didn't know that there were any 40 ch radios that were crystal? I thought they had to go to a PLL to meet the regulations for 40 Ch. I guess that doesn't help much but I am tuned in to see what the solution is.

 

[Farmer Brown]

I didn't know that there were any 40 ch radios that were crystal? I thought they had to go to a PLL to meet the regulations for 40 Ch. I guess that doesn't help much but I am tuned in to see what the solution is.

Shadetree, you are probably right, but myself, I do not know.

I'll be taking it to C.C. down in Calhoun, LA soon, he will be able to tell if it can be fixed. I have never seen one do this way.

 

[Shadetree Mechanic]

Maybe the channel selector needs to be cleaned?

 

[TM86]

If that's a model 934.38260700, it uses a SM5104 PLL. There's a thread with a schematic for that radio here:

https://www.worldwidedx.com/threads...-sears-ssb-roadtalker-40-934-38310700.231932/

 

[nomadradio]

1978 radio. Cleaning the controls and switches is a routine thing to do every ten years or so. Might make some difference.

If it was a 1978 car, you would be counting up the gaskets, seals, bushings, belts and hoses that it will need to become reliable again, even if the mileage is low.

Around the 40-year mark, it's incredibly common for the several dozen electrolytic capacitors in the radio to start going bad one or three at a time. The expression "re-capping" a radio refers to changing every last one of them. The term "electrolytic" refers to a liquid material held inside the component by a rubber gasket. The rubber shrinks with age and use, then breaks that critical seal. If the radio were NOS in the original box with no mileage, those parts might all still be good. But only for a while. The stress and heat of operating the radio would cause them to begin "remembering" how old they are. But if it has any miles on it at all the wear and tear will cause those parts to fail. A radio that old with any actual mileage usually has at least some of those parts going bad.

Of course it could have other problems besides that, but the electrolytic caps are at the top of the hit parade.

30 or 40 years ago, my "sideband operator" customers liked the audio quality of those radios. Failed solder connections on the printed-circuit board were a common fault. Probably worth checking for that, too.

73

 

[sunbulls]

Like TM86 said, it does look like a 934.38260700. It’s one of the better SSB mobile radios that are worth fixing unless the quoted repair cost is crazy high. In any case don’t toss it. Older SSB radios are always wanted for their parts if nothing else. I’m hoping you will have good luck with it. Let us know how it turns out.

 

[guitar_199]

Even PLL units have crystals in them... the reference, then usually one or two to beat the frequency of the VFO down or up to what it needs for transmit and for receive IF.
That said... it's not like the old crystal synthesized days... where 4 channels would work...then the next 4 would fail..... or every 4th channel will fail.... because you don't have the same kind of mixing.

Now, the PLL may not be locking....and most of these...when the PLL won't lock... they won't do diddly. Often they shut of receive AND transmit.

 

[nomadradio]

A good-quality control cleaner like De-oxit might very well bring it back to life. Bad contact in the PA switch is a good way to shut down the transmit side, as just one example.

First thing to find out after that is whether or not the radio is receiving on the channel that's selected. The radio has six crystals in it. They're not the most-likely items to fail. What's more likely to find in that department would be one or more crystals that just won't quite adjust onto the correct frequency.

It has 45 (I think) electrolytic capacitors in it. At the 40-year mark, they might all still work, but the odds of that are not good.

Moving parts are the first place to look, and cleaning them is the starting point to find out what it will do or won't.

73

 

[Woody-202]

A good-quality control cleaner like De-oxit might very well bring it back to life. Bad contact in the PA switch is a good way to shut down the transmit side, as just one example.
73

I don't mean to hijack a thread but... are you using the newer De-oxit with the big straw, or did you spring for the retro-fit straw @ $1.99 or move to another product entirely?

 

[Farmer Brown]

A big thank you to each of you for your comments, I will take more pics of I t soon.

 

[Farmer Brown]