I picked up this cb used with no mic. I was able to determine that it would receive when wired for a Midland mic and everything worked except for there was no modulation. It would receive and transmit a carrier (confirmed with a local 7 miles away) but there was no modulation. Upon advice from this same local it was advised that on older radios a cap, as opposed to an audio chip, was responsible for modulation and that I should recap the radio. I did just that and now there is no rx or TX. I confirmed the right caps, right values and right orientation. What I didn't check before install was that the new caps were indeed good ( brand new). So, after testing the original caps, which all tested good, I put the original caps back in their original locations but there is no rx/tx. PA does not work. The internal speaker produces hash but at half the volume level that it did originally. If an external speaker is connected a high pitched oscillating sound can be heard. Switching from cb to PA stops the hash on the internal speaker. If certain spots, or pots, are probed with a volt meter the sound level will increase. Switching channels of switching from cb to PA produces an audible click in the speaker. I've verified 13.8vdc at the red dots.Any and all advice is welcome. A schematic would also be great! Thank you in advance!
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23 ch. Smokey cb radio no rx/tx
- Thread starter Champo
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K5MPH
Member
What model is the radio......
doctordialtone
Member
It appears to be a generic. There is no model information other than Smokey written on the front (see pictures) and I cannot find any record of a Smokey company ever existing. There are also no other identifiers on the circuit board. A gentleman on another forum believes that the circuit board is similar to a Pierce-Simpson Bobcat 23 however not identical. I believe my issue may be related to my soldering skills so I will redo the cap soldering with flux rather than relying on the flux in the solder. If I can get it back to the original condition of no modulation then it'll probably be easier to troubleshoot.
It is not a Pace.
wtp
Member
a good couple of decades ago i recall hearing that some CB's need the 'right' mic cord to do anything, like RX, TX and if you don't have the mic right the PA will not work.
That was the initial thought but we were able to confirm that it was wired for a Midland mic. I have a cobra to midland adapter and without it there is no receive or transmit. With it it will receive and transmit a carrier just without modulation. At least it did until I recapped it and screwed the pooch.
I didn't see issues with bridged solder however my prep and application were not the best in retrospect. The common consensus seems to be a solder joint since everything worked prior to the recap minus modulation. I've cleaned the board thouroughly this go around and I have ordered a desoldering gun as opposed to relying on wick. I'm also going to use flux instead or solely relying on the flux in the solder. I was over ambitious and created more problems than I solved. Hopefully, with a whole lot of luck, I can at least get it back to where it was. Here is a pic of the mic connection. The previous consensus was midland wiring but I'm open to any and all opinions.
Also, I'll try to post a pic later today or tomorrow of the solder side of the board. Perhaps someone will see questionable joints, or to your point, bridges that I've missed. I appreciate everyones help! The radio is on excellent cosmetic shape and I'd love to rock it for my local Wednesday check in #WayBackWednesdays
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tvengr
Well Known Member
Take a good look at the circuit board. I suspect there is a solder bridge between foils. Microphone wiring varies from radio to radio.
Here are some picture of the solder side with different lighting.
Most of the caps were in this region (magnified pic). I found one spot that needs a do over. Only partially soldered. There are also some brown areas potentially bridging. Thoughts?
A gentleman on another forum believes the radio was made by Romar based on the act-1914 on the board. It appears in the cb-104 photofact. I just have to get my hands on one to confirm. It's not on cb tricks unfortunately.
It's in cb-104. Ironically one of the eBay sellers had taken a pic!
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Got it back to the way it was initially. Found a small piece of wick that was left behind bridging a single cap. So now I have receive and it will transmit a carrier but no modulation. I found some information regarding mic wiring from Astatic and it appears it uses 5 wires. Is it possible to make a 4 wire mic work?
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Yea, a 5 wire or 4 wire will work if you wire it correctly. Given you have RX audio, the same chip is the modulator.
Got a signal generator, find the mic in (usually coax at the mic plug) a volt P-P 1Khz into that.
Find the PTT and ground, it should transmit with modulation.
There is a transistor in the mic preamp, so last thing you need is more preamp. Just a ceramic or dynamic mic should work.
Got a signal generator, find the mic in (usually coax at the mic plug) a volt P-P 1Khz into that.
Find the PTT and ground, it should transmit with modulation.
There is a transistor in the mic preamp, so last thing you need is more preamp. Just a ceramic or dynamic mic should work.
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K5MPH
Member
Yeah tried to look up this radio on Google but nada found a couple on Ebay but dident look the same as yours,everytime you type in smokey the movie come up any way good luck on you project..........
tvengr
Well Known Member
It looks like you have some kind of corrosion on the circuit board. I would try cleaning it with alcohol. An old toothbrush will help with the cleaning. Corrosion can create leakage paths between the foils and cause all kinds of strange problems..
Just to recap what was found. Ultimately 3 transistors were found to be defective Q6, Q12 and Q13. A defective 10.625 Crystal was also found. The back swing on the meter was found to be the result of the meter wired backwards. After running the radio for a while transmit dropped out entirely on all channels. A defective transistor was found at Q15. Currently the radio is operational.
You might also want to take some rubbing alcohol & stiff brush to scrub off the flux when you're done (and before it gets too hard)-I've had some funky results from flux residue.
Glad to hear it's working!
KANE4109
Member
hey Champo! I see you are over here! Hope you are enjoying that thing.
Bob
Bob
I didn't know you were on here! I hope all is well.
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