Could use some advice on getting in to radio repair.

[Handy Andy]

As I mentioned earlier, I'm a hands-on learner and my biggest hurdle isn't so much the how, but the why. I can use a DMM and test a final, resistor, capacitor, test for continuity, etc. However, if you sat a no-rx or no-tx Cobra 29 down in front of me, no idea where to start, and if I did know which components to check first, parroting what I read or saw online, I wouldn't understand why I'm testing those components first and that is the downfall of relying on youtube or forum posts. I have a good head start in this field, more than the average joe, but achieving that level of fully understanding what this stuff is and why/how it does what it does is pretty much my only roadblock and I'm very much interested in getting to that point.

If that is where you come to see us, I'm glad you did.

We think of the forum as not just a place to discuss radio - but also have a basic set of rules that are not posted but presumed that any good tech would know to do first before arriving to a conclusion that the problem becomes larger than life and need help with others to bear their knowledge onto the playing field.

Obviously, I'm guilty. If not just producing long winded "got cover the bases" approach onto check here and there - and everywhere - may work for storytelling and learning a moral or two - but don't help the person if they don't know what to look for or how to start.

I guess we just figure the person did the right things and replaced fuses and even did continuity checks and replace or at least checked the microphone handset wiring and made sure 1 - is ground, 2 - is audio, 3 - is TX and 4 - is RX.

But why?

Ok, A cobra 29 uses Pin 3 as a means to switch on or off the TX side, so to do that - they use a PNP 2SA733 and once it's grounded - turns on a line that sends power to here, but WAIT there is another line that goes to Pin 4 that when grounded does something else - it completes the speakers circuit - Oh, so that is why you don't hear anything when the mic is not hooked up - Pin 1 and Pin 4 short to each other - oh ok...

So, yeah, I can easily see where - ok, where do I start - it's a lot harder than it looks.

So, I'm not here to dictate terms or start an argument but if you come with the basics of electronic theory and practice and have successfully jump started a car or two in your lifetime - you are pretty much qualified - with that approach, the tables become turned back to the poster and we may ask a lot of silly questions about; Did you do this? Ok, did you do that? Ok, how about this - what did you get here?

It can get frustrating...

So, in a way, you're using/developing a flow chart to determine the course of action based upon more and more specific questions to find the root or at least an answer.

​

The chart goes on and on - but eventually you arrive to a solution using / developing a path - a course of action to take - that is unique to every scenario - for not all radios have blown fuses, some have BLOWN TRACES and parts damage - so this chart can get very complex very quickly because you are trying to account for every scenario of "No Power"

So, in a way - you can catch us "off guard" when we have very little information to go on - we can only speculate - but we can guide you faster knowing that if you did this and this before you posted here, the results would whittle down the branches of the trees this radio could take us on - to just a few limbs.

 

[JDE]

Again, can't thank you enough for the information and guidance you're providing.

I suppose that leads me to the ultimate question, how do I get past that 'hump' and become the guy that says "did you try this, and what was the measurement?"

I'm mostly self taught, also took a few years of electroncis courses in HS but that was 20 years ago. I'm not against the idea of trial and error, especially now that I have a stack of cheap unknown-condition Cobra CBs from ebay sitting on the bench and I do seem to learn best from being hands-on. Thay may be the best path for me, and just leveraging the help of the gurus here if I get myself in to a rut..but I'd definetely like to get to the point where I just know and don't need to bug you guys, haha. I like the idea of flow charts, I use those often in the IT field when training new techs. That might be something I could use here to help me learn the processes and procedures in troubleshooting a radio issue.

 

[Handy Andy]

took a few years of electroncis courses in HS but that was 20 years ago.

Wow, I hope you and I weren't at the Same table when we tried to put 24 volts into a 3V DC motor...

That Teacher learned fast...

 

[Handy Andy]

I suppose that leads me to the ultimate question, how do I get past that 'hump' and become the guy that says "did you try this, and what was the measurement?"

That is a choice that is up to you - don't worry about the simple stuff, the dumbest question is the one that never gets asked...which might have the most obvious answer that no one bothered to mention.

There are several threads around here about Cobra 29's that are condensed "Cliff Notes" versions of the Service Manuals.

The one thing that is great about those service manuals are they provide help in ALIGNMENTS but offer little help in finding out why the Electrons can't perform any work. It's not that they need representation - they aren't unionized, Ionized perhaps - but they need places to go so they perform work so that means the Union of the device to the board - it's soldered, and they call it a junction - helps to complete a circuit - and it starts from there...

 

[Shadetree Mechanic]

General-class ham here, licensed for 3 years. I'd say I have an intermediate understanding of RF, electronics, and electrical components. Decent-ish at reading schematics. Many years of tinkering/soldering/etc under my belt in various other hobbies.

I've wanted to take the next step in to being able to diagnose/repair my own radios for some time now, and recently the last guy in town that handled radio/amp diag and repair for us hams in the area moved away so I figured now is as good a time as any to start learning and see if I like it enough to stick with it. Not interested in doing this for money at all, I do IT for a living and that pays the bills. This is just going to be a weekend hobby, and if I'm any good at it, something I can do for the other guys in the local ARES club. Main purpose is that it just plain interests me, and I like working on stuff like this.

I figured I'd get my start on CBs, simpler and cheaper than amateur radios, so I have a few cheap Cobra 29 LTDs on the way from eBay that probably need various repairs or calibrations. I've done a lot of googling, reading forum posts, and watching videos over the last few weeks. I have an email out to Lou Franklin to order his books and a few tune up manuals (no reply yet, he still around and selling books?), and have been browsing what I can from the mirrored cbtricks sites.

On to my question; realistically, how effective can I be at radio diag and repair with basic tools, a dmm, a dummy load, and an swr meter? At what point do I need a spectrum analyzer, signal generator, oscilloscope, etc? Are people still just finding and buying old gear on ebay? It seems anyone I watch on Youtube that does this stuff has all that, and I imagine quite a bit of money invested in to it.

Thanks for your time.

Welcome!
Here is a link to a forum that has a great section that explains radio operation and trouble shooting. Happy reading.

Understanding how CB radio works

Understanding how CB radio works

gokarters.com

 

[JDE]

Welcome!
Here is a link to a forum that has a great section that explains radio operation and trouble shooting. Happy reading.

Understanding how CB radio works

Understanding how CB radio works

gokarters.com

Just glanced at that link, and it looks like an awesome read. Definitely bookmarking and reading through it this weekend. Thanks!

 

[TM86]

Wow, I hope you and I weren't at the Same table when we tried to put 24 volts into a 3V DC motor...

That Teacher learned fast...

Had a guy next to me put a Simpson 260 into amp reading mode and jammed the probes into a 120V socket. It almost tripped the breaker, it definitely fried the meter.

 

[JDE]

Had a guy next to me put a Simpson 260 into amp reading mode and jammed the probes into a 120V socket. It almost tripped the breaker, it definitely fried the meter.

In my last year of HS electronics I was holding a kit project(not in a case/enclosure) in my hand that I had just built, something that ran off 110v. My partner thought it would be funny to plug it in. That was the first 110v hit I ever took.

 

[guitar_199]

I suppose that leads me to the ultimate question, how do I get past that 'hump' and become the guy that says "did you try this, and what was the measurement?"
I

Remember the most important dual-concept of all......

1) Good judgement comes from experience.

2) Experience comes from bad judgement.

THAT will get you FAR !!!!!

 

[nomadradio]

1) Good judgement comes from experience.

2) Experience comes from bad judgement.

I have that one on the wall under the appointment calendar, attributed to Mark Twain. It just substitutes "decisions" for "judgement". Never have followed up to see if that part is accurate. I guess he could have said it.

73

 

[JDE]

Two of the three cheap Cobra 29s I bought from eBay arrived today.

Cobra 29 LTD Classic, MFG '15, meter doesn't seem to work on SWR mode, meter jumps to and sits still around 9 on S/RF mode when TXing, no meter illumination. Everything else seems functional and no evidence of repairs/mods.

Cobra 29 NW ST, MFG '99, no power, D23 protection diode blown in half, C123 capacitor is swollen/leaking, rear power socket missing but positive and negative leads on board still there, no current draw when connected to power but also doesn't power up. Possible signs of repairs/mods, I can see what looks like some non-factory soldering on the back of the PCB and a few clear gobs of clear hot glue on the front of the PCB in certain areas, don't think it's factory. I did make the rookie mistake of applying power with the leads reversed at one point, got a little more leakage and magic smoke out of C123. I guess the silver lining here is that I learned which lead is which in a Cobra 29.

That's where I stopped on both. Got some more vids to watch, and books to read once my order from Lou Franklin arrives. Lou did get back to me after a couple days to confirm everything, those should be shipping today or Monday. Excited to see if I can save that 22 year old NW ST from the parts bin.