The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Radio was given to me, sat around for many years but looks like it had some good use before that. When i plugged it in, it's stuck on transmit...

Radio Make: Cobra

Radio Model: 29 LTD (taiwan)

PCB number: PC-900AB

PLL number: ???

IC number: D2816C

What doesn't work: Radio is constantly transmitting.

What does work: Everything else I can check while in TX mode. on frequency, modulates fine, etc.

What you have tried so far: swapped mikes. visual inspection for shorted wires, parts, etc. prodded the PCB with a sharpie here and there. small animal sacrifice to the gods.

Im hoping this is a recurring problem and the solution is simple like my last project (148 GTL) any help will be greatly appreciated!

Are you sure that is the correct PCB number, I do not have that one listed (although it could be an earlier version of something).

If the circuit design is like the current models (most likely), I would try replacing C117, as it could be shorted, in which case it could be making the transistor turn on as it could be puling its base to 0V, just like when it gets a TX control from the mic.

TR21 which is the TX switch transistor, it is a PNP device, and it passes the regulated 8V supply to turn on TX, if lifting R100 does not resolve the fault, replace it.

First try unsoldering one end of R101.
Also check the voltage on the collector of TR21.

Awesome! you guys rock. it was C117

Thanks a million!

Man, you are 2 for 2 Shadow....glad you got both radios resurrected from the dead.

well i coudln't do anything without the help of others. This is a new venture for me so it's exciting to actually see positive results.

thanks again