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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this is strange as most times if a proper transmit key is depressed , then the radio switches from receive to transmit , the mfg know this would cause some great squeal from receiver /transmitting so close to a receiver so the part that is the receiver is muted to keep this from happening , id say there is some fault in the part that does this muting of receiver
The other guest, has hit a very good point have you tried checking your mic? If not try changing it out. If you still have a problem do this; get a power meter and connect it to your antenna jack of the CB and the other end of the meter to the antenna this will put the meter in series with the CB and the antenna. then try to key the mic and speak, if the meter indicates 4watts PEP then the transmit function is working and you are getting out. The second test is to set an RF generator to 27.185MHz at -123 dbm or 5.1x-16 watts and use a 1kHz tone to modulate the signal, couple the signal to the antenna with an insulated wire loop and this will allow you to test if you can receive signal. These two tests will show if you can transmit and receive. I believe the problem is with your mic, but I have provided two tests that will prove if you can transmit and receive, so you are ready to test. Let me know how it goes.
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.
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.