Learning radio repair

[Christopher17]

Looking for recommendations for books , online courses, YouTube videos etc, learning radio repair, I have a basic understanding of electronics, 3 semesters at TSTC, I have basic tools, meters, soldiering, de-soldering equipment, I working on my ham licence, I have an old non working cobra 29 to practice on as well as my TRC-431 base station to play with, so far I've been successful in my antenna building, I'm semi-retired and my budget is basically non-existant, as time permits will funnel $$ into my new hobby.

 

[999]

Look up TRX bench on YouTube. He's really good and I think I've only seen him fail at a repair once, and I think that was due to parts availability.
Be warned though, He's in Germany and English is he second language. It's not that he doesn't speak it well, more that he searches for words at times. Couple that with the fact that he's going slow enough for a kindergardener to be able to follow along, and he can be hard to watch. (my opinion)
I still watch his videos because he conveys some really good information in every video. Just be patient and watch along.

 

[Christopher17]

did a search for service manuals hoping I could find something with test points for the non working cobra 21XLR I'm working on, no luck, schematics on CB tricks but not much else to help at this point, I don't know enough to interpret values from the schematics, I've got power , meter lights up, but no display , no sound and no key up

 

[Shadetree Mechanic]

Does the PA function work? My first guess is that the PLL is out of lock. A picture of both sides of the board would help too.

 

[Christopher17]

Will try and get a pic up, tried all functions, display never lit up, however did not connect speaker to PA

 

[nomadradio]

For me, the starting point to do anything much with a radio is the schematic diagram.

The TRC-431 owner's manual has a schemo at the end. It's posted here [URL]http://www.cbtricks.com/radios/realistic/trc_431/index.htm[/url]

The description 'Cobra 29' only narrows you down to a dozen and a half (if not more) different radios built since 1974, by a dozen or more subcontractors. The letters that come after the digits "29" will indicate which one of all those different models you have.

Best starting-level technical book about CB radio technology is Lou Franklin's "Screwdriver Expert's Guide". He also sells another longer book that goes into more depth about radio design. The title is "Understanding and Repairing CB Radios".

Lou's web site is www.cbcintl.com

I did hear that Lou had been under the weather lately. Hopefully he's back on his feet.

73

 

[Christopher17]

The experts screwdriver guide is what I was hoping for, should get me started in the right direction, thank you nomadradio , the non working cobra is a 21XLR, not a 29 like I was thinking, did some basic continuity checks, found a service manual with values for the transistors, here is the pic of the board, sorry my camera is crappy

 

[Christopher17]

Board

 

[Christopher17]

Bottom

 

[Tallman]

Sounds like the radio may have been hooked in reverse to the power supply.

 

[BJ radionut]

Don't know ANYTHING about the VID maker...but may give you some ideas at least where to start

 

[Christopher17]

Did some more continuity test, there is a PC ribbon board that connects to the display that is iffy

 

[nomadradio]

That "XLR" line of radios were Cobra's 1978 models. Not the very-first 40-channel Cobra, but still over 40 years old.

The shaky flat cable tends to be a "mileage" issue. Even if the mileage is low, it is likely to have age issues as well.

If it's just dead, the troubleshooting starts with identifying which individual circuits are alive, in particular the handful of internal power-supply voltages feeding transmit, receive and frequency-synthesizer sections.

This is one part of the picture that the Howard Sams' books present clearly.

73