Cobra 29 ltd classic

[kaos513]

Hello recieved a cobra 29ltd classic when i turn it on transistor(C2314) located by r58 rear of radio smokes like hell any help would be a appreciated.

 

[loosecannon]

that is your driver transistor, and it is probably shorted from Collector to Emitter.

Before i say anything else, what size of fuse are you using? are you using a fuse?
you need to be using a fuse, and it needs to be the right value for your application.
Not using a fuse can turn a simple repair into a pile of junk in under one minute.

remove the transistor, check it using the diode function of your DMM (google how to test transistors with a DMM) to confirm that it is indeed shorted.

then, before replacing it, put an ohm meter from the collector trace to the emitter trace (transistor removed from chassis for this) and you should see an open connection, as in NO connection. if you see a short here, then something else caused the driver to short out. Start with C216 if you do see a short.

most likely it's just the driver transistor going bad and replacing it will bring the radio back to normal operation but its always a good idea to do a little testing to make sure you aren't going to smoke your new part.

next piece of advice is don't just order one 2SC2314. take this opportunity to buy around 5 of them so you'll have them in the future.
LC

 

[kaos513]

that is your driver transistor, and it is probably shorted from Collector to Emitter.

Before i say anything else, what size of fuse are you using? are you using a fuse?
you need to be using a fuse, and it needs to be the right value for your application.
Not using a fuse can turn a simple repair into a pile of junk in under one minute.

remove the transistor, check it using the diode function of your DMM (google how to test transistors with a DMM) to confirm that it is indeed shorted.

then, before replacing it, put an ohm meter from the collector trace to the emitter trace (transistor removed from chassis for this) and you should see an open connection, as in NO connection. if you see a short here, then something else caused the driver to short out. Start with C216 if you do see a short.

most likely it's just the driver transistor going bad and replacing it will bring the radio back to normal operation but its always a good idea to do a little testing to make sure you aren't going to smoke your new part.

next piece of advice is don't just order one 2SC2314. take this opportunity to buy around 5 of them so you'll have them in the future.
LC

Tryed another one from parts radio still get same results goes up in smoke

 

[kaos513]

that is your driver transistor, and it is probably shorted from Collector to Emitter.

Before i say anything else, what size of fuse are you using? are you using a fuse?
you need to be using a fuse, and it needs to be the right value for your application.
Not using a fuse can turn a simple repair into a pile of junk in under one minute.

remove the transistor, check it using the diode function of your DMM (google how to test transistors with a DMM) to confirm that it is indeed shorted.

then, before replacing it, put an ohm meter from the collector trace to the emitter trace (transistor removed from chassis for this) and you should see an open connection, as in NO connection. if you see a short here, then something else caused the driver to short out. Start with C216 if you do see a short.

most likely it's just the driver transistor going bad and replacing it will bring the radio back to normal operation but its always a good idea to do a little testing to make sure you aren't going to smoke your new part.

next piece of advice is don't just order one 2SC2314. take this opportunity to buy around 5 of them so you'll have them in the future.
LC

Donot see c216 not even in the manual parts.

 

[kaos513]

Original and parts radio transistors are shorted view picture.

 

[loosecannon]

did you check for a short between the collector trace and PC board ground (the emitter of the driver and final transistors go to ground) while the transistor was out of the radio?

the reason i mentioned doing that test in my first post was to avoid you putting in a good transistor and having it go bad too.

As for "C216" that is my bad. I meant to type C126 which goes from the collector trace of the driver to ground. If this cap is shorted, then any driver transistor you put in there is going to short out.
Dyslexics untie!!!

we need to find out what is shorting that collector trace to ground.
LC

 

[kaos513]

I did the following above after replacing the cap i do not get any readings on my volt meter

 

[kaos513]

I fixed the issue was the final was shorted as i was getting really low numbers on the one on the radio so i used one from my parts radio works great now no more smoke.

 

[loosecannon]

congratulations!

As i know you are interested in learning more about troubleshooting radios and electronics; remember this method the next time you find a shorted/blown part.

With the bad part removed, take a measurement or two on the now empty traces and interpret them to help you find the cause of the failure.
LC

 

[kaos513]

I talked to a buddy mines he said he tryed a variable mod so he gave up on it ,he must of blew the final.