I have a Maxon MCB-55 which I am unable to transmit or receive with. When I key the mic, other CBs recognize the signal and the meter moves; however, no sound is transmitted. Furthermore, when I key the mic on other CBs, the meter moves on the MCB-55, but no sound is heard. Also,when I que into the weather W1-W3, I do not receive any sound. I have checked the antenna and know that it is working; I have also read several posts on here and have already checked the solder joints, but that has not fixed the issue. Any suggestions?
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I have one that doesn't transmit between the two we could have one radio but who's.. you should try to tune the receive cans but with no schematic you can't because if you turn the wrong one you could kill the radio. I would buy another radio like a radio shack trc - 503 or something in that line if you're into small radio's. Some of them can be opened up to talk like a big radio.
Check you mic first to see if it is indeed working. Then if it is the below advice is applicable. It sounds as if your TX audio amplifiers might be malfunctioning or the TCXO might be bad. If you have a background in Electronics I would suggest that you open up the unit and using a dummy load on the antenna check the two TX audio amps to see if when you key the mic and speak into it the amplifiers are amplifying your voice and sending it to the modulator. If the problem is not amps or the filters in between the amps, the modulator and the VCO buffer are suspect. If the TCXO is being modulated I would check the PPL IC and the Drive amp to see if the modulated signal is getting through. The last two checks I would perform are on the final amp and the TX switch prior to the antenna jack.
If you do not have a background in electronics, still check your mic, but the rest of the above advice can be done by a qualified Radio Technician.
Moving the volume/on/off knob to make the radio work again is interesting and a good clue. On most CB's, the pot is probably soldered directly to the printed ciruit board.
It's possible that there is a bad solder joint to the power connections on the pot that turn the radio on & off. If the solder joint is bad, it can still make a connection but the connection will have added resistance in line. The on/off switch can be bad too. Switches arc each time they are used and over time, the contacts become pitted and make poor connection.
I had a stereo receiver where the tuner lights flickered and there was electrical noise in the receiver. It turned out to be a bad on/off switch.
This resistance may be low enough not to affect the radio when in the receive mode but when you transmit and draw more current that resistance will be noticable during transmit.
The fact that you rotate or move the volume/on/off knob and the radio starts working again, tells me that there may be a bad connection in the radio.
A cheap thing you can try is spraying some electrical contact cleaner into the pot and rotate the pot back & forth several times and turn the switch on & off several times to clean it.
Please let me know if I can be of further assistance to you.
I recall the combo unit as I used to sell them. I am about sure they are no longer avaidable. You never know, you might see something on ebay/auction sights that might be to your liking. Good Luck.
In order to test this unit you will need a power meter with a dummy load. connect the power meter and turn on the unit, key the microphone and look at the power meter it should have a reading of < 4 watts PEP unmodulated and = 4 watts PEP modulated.
If you do not have this reading the RF transmitter in the CB might be malfunctioning. You will need a RF generator, a power meter with dummy load, oscilloscope and a multimeter to troubleshoot this problem with. If you do not have or do not know what this equipment is or how it works, please take your unit to a CB repair shop.
I'm not sure about your particular model but many CB radios use the microphone push-to-talk switch to kill the speaker while the radio is transmitting. If you don't have the correct microphone or if the cord has a broken wire it can cause the radio to have no sound. Another possibility is that the speaker is bad. There is probably an external speaker jack on the back of the radio. You could try plugging a different speaker or even an earphone in the jack to see if you get sound there.
You might have a loose wire in the mic plug, also in the plug itself there are 4 holes for 4 pins in the radio to fit into, these 4 holes have tiny metal sleeves in them to make contact with the radio pins. these sleeves are split and you can take a tiny jewlers screwdriver and slightly close up these sleeves this causes them to fit tighter on the radio pins creating a better connection. these sleeves WILL over time spread out causing the radio to lose a function such as receive or transmit I have encountered this problem several times in the past at my shop. Good luck on your problem.