What are these pcb components?

[jimbowilly]

I would like to know what the parts circled in yellow and in red are. What basic function do they perform. I'm not asking what function they perform on this printed circuit board. I would just like to know what they are and how they function in radio electronics?
Thanks,
Jimbo

 

[Robb]

Some of the ones in yellow tune/align the receive, others tune/align the transmit. Others set the voltage/amplitude for the VCO and one sets the transmit/receive frequency. I think one or two of them tune the noise blanketer too.

The ones in red adjust the meter for receive, another for meter adjustment for transmit. I think one is also a modulation adjust. Been awhile since I last aligned a Cobra 29. Been awhile.

Don't mess with ANY of these parts unless you are willing to live with the consequences. Or pay a radio tech to put them in their proper state of tune again. Messing with them is NO WAY to get more out of your radio - unless you know what you are doing AND have the required equipment. If you want more out of that radio, let a pro do it. It is worth the $30. If you need more power, just get a small linear - if you must. Just tell the tech to set it up for the linear, and supply the linear that will be used. This way, he can match it up to your radio. Job done right . . .

 

[Simon004]

I'm not asking what function they perform on this printed circuit board. I would just like to know what they are and how they function in radio electronics?

Robb gave you a good breakdown of what they do in that particular radio, but I don't think he read your post properly, lol.

The ones in yellow are tunable inductors (coils), just the same as the other coils that you see on the board there. The difference being they have a slug inside the coil that you can move in and out by adjusting the top of them, this changes the value of the inductor.

The red ones are potentiometers (old name) or variable resistors (new name). Just like any other resistor on the board, but by turning them you can adjust the resistance value. Typically they have 3 terminals, the 2 outside terminals remain a constant value to each other, while the middle pin is connected to a "wiper" which you can move around to achieve any resistance from 0 up to the maximum value of the resistor.

 

[jimbowilly]

I would like to know what these components are? (What I would ask for if I were buying them from a electronics supply retailer.) And how they function as components period.

And taking my radio to professional for adjustments wouldn't be any fun now would it?
I would imagine each and every "professional" miss aligned his/her share of radios in the beginning.
Or are there people born with the ability to fix radio?
And I'm working on the "required equipment".

 

[jimbowilly]

Thank you Simon004,
Just the answers I am looking for.

 

[Robb]

A 50mhz oscilloscope, a frequency counter with 10Hz resolution, a digital multimeter, an accurate watt/modulation meter, and a RF signal generator. Nylon screwdrivers and other adjusting tools. Frequency sampler and other misc stuff too.

Then knowing how to use them all and extracting the info. Knowing that the gear is set up properly and is accurate is a must.

AS Simon said, they are coils in yellow/variable resistors in red. They will fine tune different aspects of the radio. Adjusting must be done in the proper order too. I'm all for it if you are willing to learn, as I have been doing this for myself and others in my part of the world with a fair success rate too. But it takes a lot of patience and understanding how to use the equipment properly. I didn't start out doing AM radios; I learned on the AM/SSB radios. Still learning too. Measure success one radio at a time.

Start out with a radio that you can get the alignment info for, and that isn't a major loss if you bone it up. Take one step at a time, and try to make sure that the radio is still working after each step. Write down the values that each adjustment point had before you made a change.

Go for it.

Radio looks to be a Cobra 29; alignment info is available on CB Tricks - BTW. They don't have alignment info for every radio; but they do have it for a bunch. What they don't have can be had at SAMS CB Photofacts (online) for $22 a pop.

 

[jimbowilly]

Thanks Robb. All great stuff !
I've just become 50 yrs of age. I figure I still have time to fill my bench with all the right equipment for my wife to sell it all when I'm gone and pay off the mortgage.

Thanks
Jimbo

 

[loosecannon]

jimbowilly,

if you want to learn about the insides of the radios, do yourself a big favor and go to this website:

CBC International - books plans kits modifications repairs for CB radios

its a business called "CB City International", and its owned by a guy named Lou Franklin.
he's been around forever, and has written what are IMO the two best books a beginner can get on CB radio repair/modification.

buy the "Screwdriver Experts Guide to CB Repair" first, or at least read it first.

then, once you undersand what's in that book fairly well; read "Understanding and Repairing CB Radios".

this is what you are looking for.
LC

 

[Beetle]

The red ones are potentiometers (old name) or variable resistors (new name). Just like any other resistor on the board, but by turning them you can adjust the resistance value.

"Potentiometer" is not an old name. A variable resistor only has two terminals, whereas a potentiometer provides a fairly constant load between the end terminals but allows a portion of the total voltage developed across those two terminals to be shunted off to other circuitry via a third terminal.

You can connect a potentiometer as a variable resistor by simply using one of the end terminals plus the wiper. The whole component is still a potentiometer, though.

 

[Captain Kilowatt]

"Potentiometer" is not an old name. A variable resistor only has two terminals, whereas a potentiometer provides a fairly constant load between the end terminals but allows a portion of the total voltage developed across those two terminals to be shunted off to other circuitry via a third terminal.

You can connect a potentiometer as a variable resistor by simply using one of the end terminals plus the wiper. The whole component is still a potentiometer, though.

Wouldn't that make the potentiometer a rheostat then?

 

[Beetle]

Wouldn't that make the potentiometer a rheostat then?

By function, yes. But the component as a whole remains a potentiometer.

 

[Robb]

jimbowilly,

if you want to learn about the insides of the radios, do yourself a big favor and go to this website:

CBC International - books plans kits modifications repairs for CB radios

its a business called "CB City International", and its owned by a guy named Lou Franklin.
he's been around forever, and has written what are IMO the two best books a beginner can get on CB radio repair/modification.

buy the "Screwdriver Experts Guide to CB Repair" first, or at least read it first.

then, once you undersand what's in that book fairly well; read "Understanding and Repairing CB Radios".

this is what you are looking for.
LC

I sent an email to Lou Franklin the other day. I asked him when the book "Understanding and Repairing CB Radios" was going to be reprinted and re-released. As it was supposed to be coming out soon, and he said that is so.

He said that I am now on his mailing list and would be notified the second the book was available.

If any are interested in getting a copy, just send him an email from the site that loosecannon provided above. Ask for notification for this book. I've seen them going for $60 on eBay and are very hard to find at that. I think Lou Franklin will be selling the book for $42 plus postage from his website. This book has also been revised/updated.

Am reading the "Screwdriver Expert Guide" still.
It is a little old and dated; but the info is still pertinent and usable. It is also recommended that you get a copy of that book first as a primer if you don't have enough experience with understanding electronic components (resistors, diodes, coils, IC's, crystals, transistors, capacitors, transformers, etc...) or radios in general and its related equipment.

 

[jimbowilly]

Thanks for the information.
The "Screwdriver Expert Guide" is on it's way to my house.
Sound like it will be a great help in my learning radio electronics as a hobby.
Jimbo