Quote:
Originally Posted by
hi not sure if you have fixed the radio at all but it sounds like the final or driver or both have failed , this is what gives the rf power output , these to transistors are based usually on the rear of the radio chasis most common part numbers for driver is 2sc2166 / PA is 2sc1969 you might find one or both transistors have failed and pulling the postive rail to ground rail ( hence the dimming of the radio) parts should cost around $20.00
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The problem is - if a service tech charges $40.00 to repair it and $20.00 of parts - you now have $100 into a $25.00 transceiver - with no warranty.
THROW IT AWAY!
SELL IT
OR USE IT A A DONOR RADIO
There isn't a lot of high technology in a AM CB radio.
But for a person that does not even OWN a VSWR meter or a VOM meter - I can't with a straight face - tell them how to repair them and guarentee them that their repair - with no technicial experience or background - can fix it.
You would want to use some type of heat sink when you soldered the transistors in and you would want to replace what ever else it took out when someone operated it with a bad match - which is usually what takes most finals out. Or a near lightning strike - which fries more then just the transistors.
http://www.cbtricks.com/radios/cobra/139/index.htm
When you take the 4 screws out of the back and the one big screw from under the radio, it will slide out of the cabinet.
If you look on the one side - you will see 3 transistors - those are the first place to look.
Cross reference them via online - see if they are PNP or NPN transistors.
NPN are the most common - since they are cheaper to manufacturer.
USE A VOM METER that has a transistor checker and do a internet search to find the gate, drain, source - to check them out.
Then I would throw them away and put new ones into it and see if it now works.
With a radio of that age, it probably needs all the capacitors replaced also - which is very expensive.
Even after all of that, usually one of the bulbs - (AM) goes out in the display - since it was used the most.
The switches will need cleaned, the pots will need cleaned, the selector will need cleaned and adjusted.
After all of that, if you are really lucky, it will work again, like it did 30+ years ago when it was new.