I am new to repairs and only recently got interested in fixing and toying with old radios so please excuse me if I sound dumb. I have a few older cobra 29s and a few other brands l would like to get up and running. The one in question powers up and has some nasty static on Rx and the light goes red on Tx but I hear no chatter and the meter doesn't move on key up. I was told that the driver and final could be bad and to try replacing both and go from there. My question is, since the original transistors are almost impossible to get, and MOSFETs require some changes that I probably would screw up, what would be a close drop in replacement for something like the 2sc2078? And a good driver?
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Driver and finals
- Thread starter Keith710
- Start date
Welcome to the forums, first you will need the schematic, for each radio if dfferent model,then you will need a multimeter to test one transistor at a time,schematic usually would come with voltage chart for each transistor.
Thanks. I do have some schematics at home for a few cobras and a galaxy I believe. I'll take a look at em tonight.
Welcome! It is never too much to be afraid to ask a question. Knowledge and skill is not free and can be hard to find in the world! Good luck!
It is when people will not try to do anything for themselves that I have disdain for them! Like when they can not be troubled to google something like "MRF455 for sale" and instead want you to do it for them!
Cheer!
I don't remember asking anybody to Google anything for me. If you think I haven't googled, read forums, read manuals, and tried fixing them myself for countless hours at night on my days off you are dead wrong. See if you read my post I clearly stated that I'm only a few months into a hobby I just fell upon one night when the radio in my truck stopped working. Drove over 700 miles back home and not one CB shop was still in business or at least open at the time. So I decided to take on the task myself. Luckily it was easy to find and I had a soldering iron laying around so I fixed it. Now I can't afford to quit my job and go back to school to learn the trade or I would. But thanks for your reply and the mention of the part. You have a nice day and keep your sarcastic shit to yourself.
The 2sc2078's are easy to get a hold of and the 2sc1957 drivers are also easy to get a hold of. I would remove the components and test them before replacing them. Somewhere on you tube I saw a video how to test these transistors with a VOM if you do not have a transistor tester. It will be a fun learning experience.
Yeah I found some online from a few places. I've ordered a few parts from rfparts before and they were good so I'm gonna give them try. So many fakes floating around these days. The final checked ok but someone has been in this radio before. The driver was changed to a c2314 and some resistors and a few caps were changed. I have replaced those with the value according to the schematic but I still only get 9.6 volts. Checked the power connection before it reaches the board and get 13.8. I might try a simple alignment. I have a scope and signal generator but it's been a long time since I've used them. And really didn't pay much attention in class lol. But I was a kid in high school back then and my mind really wasn't into electronics. Thanks for the reply
Probably would help a bunch if you mentioned the make and model of the radio you are now working on. I am assuming a Cobra 29? You only mentioned you had a few cobra 29's and a few other brands of radios. so it will be hard to steer you in the right direction without knowing the radio you are working on.
Yeah sorry. It is a cobra 29 LTD. I'm giving up for today, mainly because I have to hit the road in a few hours but I appreciate the replies. I'm gonna order some drivers and finals today and try again next weekend.