Have a fidelity cb3000 homebase radio and require assistance to mic wiring internally to the mic itself. there are 6 positions to solder and several of them have come off and can't remember what colour wire goes where. it is a four pin mic which have never been touched but its the mic end itself where the joins have been worn. other details are that it is a basic mic nothing like a power mic. Regards Simon

the rf power going out is geting inducted on the wires of the mic.try using some ferrites close to the coax on the pl259 connector and on the mic wire itself.

CBTricks Radio Info check this for mic wiring and resolder

Hi Davey,

You have a Radioshack PRO 505XL, and I take it that you have the mic connected to the set and not using the internal mic, is this correct?

If this is so, the problem might very well be the wrong mic for that radio brand & model, or if it's the correct mic, then it's a dead mic, but if you're referring to the radios internal mic, then it could be a wire has come lose or that mic needs replacement, which ever it is, it means replacement or re-soldering.

I hope this has been helpful.

Cheers,
Peter

Your mic has a series of contacts which cut off the speaker before you transmit and activate the transmitter. If the mic has screws holding it together. With the radio power off. Open the mic and check the spacing between the contacts if it is not enclosed. Some are sealed in a casing. You want to verify that the contacts are not sticking or too close together allowing other functions to stay on.

If you cannot check the contacts. Unplug the mic connector. Get a copy of the mic wire functions and use an Ohm meter to verify that the speaker leads disconnect when the mic button is keyed. It should read "0" when the mic button is pressed. If not, then there is a problem in the mic button switch and you will need a new mic.

Carefully inspect the mic cable for wear breaks. The wires inside are easily damaged when the shielding is damaged. Cables can be repaired. Be sure to slide on two to three shrink tubes to cover the repair job when done. Slide on the tubes and heat them one at a time to create a good protective shield for the wires. This involves several solder connections which will need a small shrink tube on each wire solder. Electrical tape can be used but it will end up a large bulge in the cable afterwords. This should be considered a temporary repair since the strength of the mic cable will be compromised. Stretching the cable afterwords can result in a wire break.

Next check the connector where the mic attaches to the radio, Often there are two small screws which can be removed so you can check the wire connections. A lose wire may be making contact with another contact when the mic is moved around allowing the speaker to stay on during transmit. A small lose strand of wire will account for the noise. After a lot of use the contacts in the plug can become lose if you frequently stretch the cord pulling on the connector. If it is the problem make a note of the wire positions. Then remove the leads with a solder iron. Be careful not to overheat the small metal post as the posts are seated in a plastic mold which can be damaged when overheated. Slip shrink tubing onto the mic cable. If the clamp was not very snug use more than one piece of shrink tubing. Cut off the bare ends and strip back about a 16th (just enough to solder back on). Re-solder the fresh wires to the pins. Over time the wires going into the solder weaken and break. Make sure there are no lose wire strands which could touch another pin. Slide down the shrink tube as far as possible and heat with a match or lighter. Re-attach the clamp so that it holds the cable snugly.

If the problem is not in the mic switch, cable or connections, you will need to take the radio to a technician.

You can also check for mic related problems by using a known good mic. However it should be for the same model radio. Pin numbers and configurations vary between radios, even the same brand of radio. Just because it fits the connector does not mean it will work properly and can even damage the radio.

This one you will need a digram. any wiring you need is on that page. Good luck. www.cbtricks.com/radios/cobra/29ltd_29ltd_st_29wx_st/graphics/cobra_29ltdwx-st_29ltd_sch.pdf

there a several things you can check yourself with a minimum of tools or test equipment. this model has been around for several years and voice coils do expire in the internal speakers as they age. attempt to locate a known good external speaker with a 3.5 mm plug and see if the receiver can be heard through it. if so then the internal speaker has seen better days and the solution/s should be obvious. also in this particular model the receiver output is controlled by the microphone switching and an open receive line in the mic cord/cable or the plug itself would render the receiver unhearable. check with another known good microphone wired for realistic radios (5 pin DIN). the microphone might also have been rewired improperly. make sure the squelch is in the fully counter-clockwise position and the volume is adjusted to a suitable level while testing, 12 o'clock or higher.

there are several things that might be responsible for the absence of modulation when speaking into the microphone. a defective mic cartridge, a broken audio or audio shield/ground wire in the mic cable or mic plug or a defective push-to-talk switch in the mic itself, for starters. if all is well here then the amc and transmitter speech stages in the transceiver will have to be considered next. locate and check with a known good mic wired for the radio in question. let me know.

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.

Good luck!

- Jim