Coincidence?

[troutscott]

The battery in my power mic died so having trouble finding a replacement I ordered a in-expensive replacement mic for temporary use.
I received the mic and plugged it into my Realistic TRC-431.
After keying it up a few times all of a sudden the modulation light sticks on,meter light dims and receive meter goes to zero.
I smelled hot electrical so I let unit cool down-unplugged it and opened it up.
The 120/12 volt transformer was super hot.
Each time I turn on unit now the Mod light is stuck on,lights are dim and meter is at zero.

Any ideas?

Thanks,
Scott

 

[jonwienke]

The replacement mic is probably not wired correctly for your radio, and there is a good chance you have damaged it.

Given the number of different CBs and mic pinouts used over the years, unless the mic is made by the same manufacturer as the radio and specified to fit your particular radio model, the odds are that the mic pinout is different than what the radio expects, even if the plug fits the radio correctly.

You're probably looking at a repair or a new radio.

 

[troutscott]

Thank you for the informative response.
I have a call into the mic supplier to see what they will do.

 

[jonwienke]

Most likely not much, unless they advertised the mic specifically as a drop-in replacement for your radio. If not, then the most likely answer will be that it is your responsibility to make sure the pinout of the mic matches the pinout of the radio before you plug it in and fry something, and they won't accept responsibility for damage to the mic or radio if you failed to do so.

 

[DJ11DLN]

Been many years since I fooled with CB but I recall all of those different pinouts for different brands -- even different models of one brand -- using the same plug being a pretty big PITA. Bottom line, check the specs before you plug it in...if it isn't right some basic unsoldering/resoldering is the solution.

In this instance I sincerely hope you didn't turn your CB into a doorstop.

 

[prcguy]

I've never heard of a radio being damaged from plugging in the wrong mic and there should be no damaging voltages at the mic plug. What can happen with a wrong mic is the radio will go into transmit mode continuously and eventually heat up the transmitter and power supply, but you said the new mic worked ok on transmit a few times before the problem showed up.

I think your radio simply died of unknown causes and the dim lights are an indication something is drawing way too much current as evidenced by the power transformer getting hot. That should not happen if the wrong mic is unplugged since the radio would not be transmitting.

 

[RFI-EMI-GUY]

You can find the manual including schematic here:

http://www.cbtricks.com/radios/realistic/trc_431/graphics/trc431_om.pdf

Mike wiring details here:

Realistic NAVAHO TRC-431 (21-1544)

I would get the original mike fixed and use it to troubleshoot the radio. an improperly wired mike could have shorted pin 5 of the mike connector to ground resulting in loading the secondary of the audio/modulation transformer. It is unclear if this winding contains DC,(Point "E") but I suspect this winding is modulated DC for the power amplifier. If you look closely, this winding is switched to a rear jack for PA function (CB/PA S2-4).

If you can isolate the power supply (S6?), I would begin by some basic DC voltage checks to see if a power supply pass transistor failed. Your nose and eyes might find a burned resistor or other component. It looks like a nice vintage radio worthy of repair. Not sure I would pay for such service though.

Some of the schematic, especially around the mike connections depict some possible errors, so in your troubleshooting, use an ohmmeter to reverse engineer the schematic or your head might spin.

 

[troutscott]

Thanks for the responses and the links.