# CB radio repair



## Sicklyboy (Mar 20, 2012)

Decided that after having it not work for over 5 years, I'd take a look at my dad's *Uniden PC76XL CB Radio* since I have a better understanding of electronics than I did when I was 15.

Problems:
-Parts of the channel LCD fade in and out from time to time.  I am not worried about this at all UNLESS it is a symptom or the cause of the root problem.
-Unit doesn't seem to broadcast or receive transmissions.

What I know:
-Unit successfully powers on.  Currently powering it with the 12v lead off of a PC PSU.
-Internal speaker *works*, external CB and PA outputs also function, HOWEVER I am not sure if they function properly (as in if whatever controls them is malfunctioning).

He's using a "Lil' Wil" Wilson antenna and an Astatic D104-M6B mic.  On the antenna, part of the tip of the pin is broken off, but has been tinned on the broken bit to protect it. I am not sure if the mic works or not.

In fact, my dad and I are both wondering if the mic is the cause of the problem.  We both don't know if a CB will work without a mic/without a functioning one.  When I plug my headphones into the PA output jack, I hear a faint hum, then when I click the mic in the hum fades out (think the cliche "power stations dieing during a blackout" from all movies) and then nothing.  He has a 2nd mic, but we have no idea where it is.  Within the next few days I'll be pulling the mic apart to check the continuity of all of the components in it.

The squelch appears to work - static when it is turned all the way down, and it is reduced/eliminated when you turn it up (only hear the hum).  Not sure if mic gain works.  RF gain makes the static louder, so maybe it IS receiving.  I have -NO IDEA- what delta tune does.  SWR gauge lights up but doesn't move regardless of what the SWR CAL knob reads, whether I am "attempting" to broadcast or not.  the RX/TX light is on when listening, dims a bit and the "ANT" light lights up when I try to broadcast.  CH9/Normal switch works as expected.  BRT/DIM switch brightens or dims the channel display, as expected - but has an effect on the pitch of the hum.  CB/PA switch works.  I have no idea what the "NB/ANL"/"ANL"/"OFF" and "S/RF"/"SWR"/"CAL" switches do (two three-position switches).

Anyone here got some input for me?  I would LOVE to get this working again for him, he'd really like this... I hope we have some CB pros here who can help


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## 431unknown (Mar 20, 2012)

I'm not a pro but I'd suggest looking up  the pin out for your mic you have and the spare when you find it incase you would need to buy a new one. Truck stops are your best bet for this as most will have a CB shop inside.  Also make sure that your antenna has the right grounding plane ( if it is magnetic make sure its on a piece of metal that is grounded if its not magnetic ground it). The tip being broken off could affect preformance but it really shouldnt matter unless the antenna is not properlly tune to begin with.  It would be best if you knew someone with a cb so you could really check if you're reciving and or transmitting. The hum you hear could be from the power supply your using as I always had hums when using one of my CB's ecspecially in a car.

It would be cool if you could get it working and were able to find a base amp. Base amps are highly frowned upon by the FCC and are illegal but are not hard to come by (I bought one about 10 years ago. It's a 250 watt with built in upper and lower side bands). We could then chat with each other tho I must admit none of my stuff is hooked up at the moment. I always meant to put my antenna up when we moved into this house, but sadly never got around to it.

If you do get it working take it to a decent CB shop and have it "super peaked and tuned" as most CB's sold are limited to 4 watt transmit power but are capable of slightly more.


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## Sicklyboy (Mar 20, 2012)

Forgot to add that - yeah, my dad's CB is pre-peaked and tuned by the guy who owns the shop he got it from way back when.

So, a few additional notes and questions now that someone has replied:

-Will a CB work without a properly functioning mic?
-What happens if a ground-plane antenna isn't properly grounded? (the Lil' Wil is a magnetic one)

I tried this antenna on top of my car, and i still got nothing.  I asked my dad and he said channel 19 is a fairly active one around here, but I've yet to hear anything.  a static crackle here and there, but otherwise nothing.  The SWR gauge has now moved, and it has gone all the way to the far right and stayed there.  It was only moving if I kept pressing and depressing the mic key.  The hum-fade when I press the key also plays over my stereo speakers for some reason - I am assuming this is from the antenna, which is currently stuck on my floor vent.  If a proper ground is needed, I can stick it to my PC case, though I don't really want to lol...


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## 431unknown (Mar 20, 2012)

An improper ground plane will eventually fuck the radio up, but since you state it is magnetic when you put it on your car it will be grounded thats how they are designed. A messed up mic might make the radio not work right, but I'm not sure. I would think that you should still be able to receive.

here is a link for setting SWR ignore the separate meter if your radio already has one built in.

19 is the commonly used trucker channel if you are on that channel you should hear some one tho since cell phones are more prolific than they were in the past that could be why you hear nothing.

Here is another link that talks about proper antenna tuning and SWR tunning.

your swr sounds high to me if it's all the way up it almost sounds like your radio is stuck in transmit mode but you say you hear static and you should hear nothing when in transmit mode since you are not recieving. Your mic maybe the problem. How old is the radio? It is possible there are some crossed wires some where in the mic.

A common rule of thumb that I always hear was that your coax with attached antenna should be in multiples of 3 foot lengths tho I have read other wise.


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## Sicklyboy (Mar 20, 2012)

Hmm.  Here's an interesting discovery that I am very excited to have found:

His Astatic D104-M6B mic is a powered mic (which you may or may not know).  I had already opened it yesterday, but paid no attention to that fact.  I opened it today just out of a gut feeling to look at it, and not only was there no 9v battery in it, but the negative terminal on the PCB had broken off (so THAT's what this little metal piece in there was! it's still on my desk).  Luckily I have a few 9v battery clips laying around here somewhere, so tomorrow I am gonna pop off the positive terminal on there and solder the clip on.  That should at least let me transmit, which I won't know if I am if I'm not getting a response, but I could see it as a valid possibility that not having the battery in there is making a circuit be incomplete that is essential for receipt of broadcasts.  In any event, it's a problem that needs to be fixed.

And for what it's worth, he said this CB is anywhere from 7 to 10 years old.


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## 431unknown (Mar 20, 2012)

That is probably your problem then. Let me know how it plays out for you. 

I own a Uniden and it's been so long since I looked at it really good that I can't tell you the model. I also own a Cobra (again unsure of model) and my dads old bobcat that's only like 20 channels or something.

I know when I bought the cobra it was like a 200$ radio (20 years ago or more) and the uniden was around 50-70$.

If your interested I'll dig them out and post the Models #'s sometime.

Does the mic have a roger beep and echo effects? Or is it just an voice amplification type?

Also if your interested I can dig out the base amp and give the details on it also.


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## Sicklyboy (Mar 20, 2012)

Not sure on any of those details, but I -think- the mic does have a roger beep, not echo though (what does that do?)

There is a dial on the back labeled 1 ... 5... 9, I am assuming this is a selector for the level of amplification.

Edit - also, after looking at the FireStick page, I am getting the impression that "ground plane" is actually a metal surface solely for reflecting the signal back into the air, not creating an electrical ground.  Am I horribly false in assuming so?


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## SickPuppy (Mar 20, 2012)

If you're not close to an active area, then the lil willy may not be recieving any signals. I noticed with my lil wilson it would only receive really strong stations, or somebody using an amp. You may want to get a meter to check that the antenna is properly matched, that will also tell you if your coax is messed up. Sometimes, with repeated kinking of the coax (closing a car door on it) it will become faulty and have a bad match with the radio.

stick the magnet on the top of your car, not the trunk. The trunk lid will not give a good ground and your reception will be directional. Additionally, run a wire from the frame of your radio to some thing metal in your car, this should improve the grounding.

the dial on the mic may be for echo or modulation or reverb?

My radio collection includes a Uniden Bearcat 68 xl, (2) 142GTL base radios, President Washington, Uniden Grant, 148f GTL, and other lesser radios. I used to hang out on 26.895 am, but it's been a few years.


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## 431unknown (Mar 20, 2012)

plasma dragon007 said:


> Not sure on any of those details, but I -think- the mic does have a roger beep, not echo though (what does that do?)
> 
> There is a dial on the back labeled 1 ... 5... 9, I am assuming this is a selector for the level of amplification.
> 
> Edit - also, after looking at the FireStick page, I am getting the impression that "ground plane" is actually a metal surface solely for reflecting the signal back into the air, not creating an electrical ground.  Am I horribly false in assuming so?



Echo is echo. It makes your voice come across to whoever is receiving and listening with a slight echo. 

You are. correct in you assumption about a grounding plane and what it is for.


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## Sicklyboy (Mar 20, 2012)

Replaced the battery clip in the mic and put a very used 9v in, but it still has a bit of a charge.  With headphones plugged in, the PA function works perfectly.

The CB may or may not.  As I don't have it set up on a ground plane yet, I am sure the signal is garbage, and the SWR is still above 3.  I'll have to set it up on top of my car tomorrow afternoon to check it out.  In any event though, I got one issue solved at least.

But after calling a few mic checks with no response on 19, my little brother storms into my room and asks "Nick, what are you doing?  I keep getting feedback and tests over my speakers."  (his computer speakers have a bad volume pot (another thing I need to fix) so I told him to keep them on all the time and control the volume with his keyboard).  Told him to go back to sleep, as it's 1:30 AM here.  I feel kinda bad, but it's kinda funny too.  I was calling myself by the handle Tech Guy (which thinking of it I'm not crazy about) so it'll be funny to see if that's what he was hearing.  If it is though, then it seems likely that everything works   If not, he was probably hearing the short range interference that was hitting my stereo speakers here too.


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## 431unknown (Mar 20, 2012)

Hopefully it's fixed. If his speakers were picking it up then more than likely it is even if it was just interference since the CB would have to be transmiting to cause the interference. Have you gone around the dial doing mic checks or did you just stay on channel 19?  

I think I'm going to have to set my stuff up here soon especially if you got yours working just so I can see if you can hear me with my base amp running.


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## Sicklyboy (Mar 20, 2012)

I just did a mic check on 19 I only did mic checks on 19, but I am gonna actually hook it to my car battery today and stick the antenna on the roof and go for a drive and see what I can get.

How far are you gonna be setting up?  I'm around the area of the Seaside Bridge here in NJ.


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## Sicklyboy (Mar 20, 2012)

So.  Went for a drive with it, hooked it into my car stereo (it has a line-in).  Under the PA jack, I heard myself coming over my speakers, as expected.  When hooked up to the CB external speaker jack, I did hear talkback from my mic, so the mic works, however I called a mic check on almost every channel and got nothing.  My SWR is still almost maxed out (It's above 3, in the red) and I can't figure out how to lower it.  The SWR calibration knob on the CB *nudges* it ever so slightly down if I turn the knob all the way up, but not enough where it is where it needs to be.

Thoughts?


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## 431unknown (Mar 20, 2012)

Try new coax and or a new antenna, also are you sure that the antenna is properly grounded to the car body?

Is the coax attached to the antenna as in it's all one piece or does it screw off?


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## Sicklyboy (Mar 20, 2012)

Not sure exactly what a proper ground would be for it, it WAS stuck right in the center of the roof of my car.  The coax is one piece, only screw part is the connector from it to the CB (and of course the mic).

The SWR gauge needle also doesn't move back down to 0 when the radio is powered off, it stays in the red.  Regardless of power or anything connected to it.


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## 431unknown (Mar 20, 2012)

Then the SWR meter might be broken. I'm very suprised that you are not able to find one person on 19 to talk to while doing mic/radio checks.

As for making sure you have a proper ground I would just run a wire from the coax connector that plugs in the back of the cb to a screw that goes into any part of the metal frame /body on your car .


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## Sicklyboy (Mar 20, 2012)

I'll have to try that tomorrow.  For the ground wire on the CB end, would squeezing it behind the nut keeping the coax connector pulled to the outside of the radio suffice, or should I actually solder it on somewhere?

And thank you for all your help so far with this   I really hope I can get this working for him.  He said the amount of feedback (the humming) it's producing never happened back when it did work, that combined with no response even on 19 is making me feel quite pessimistic about this though :/


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## 431unknown (Mar 20, 2012)

Putting it behind the nut should work no need to solder anything yet.

As for the humming they make interference filters that help with that.  I'm thinking that now your problem either is in the coax and antenna or the radio itself.  I'll have to go digging in my basement to see if I still have it first, but I might have a spare magnetic whip that your more than welcome to try.  I'd be interested in knowing the total length of your coax and antenna, if you don't mine measuring them.

Your welcome for the help.


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## Gahars (Mar 20, 2012)

Listen to Convoy until the radio mans up and fixes itself.


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## Sicklyboy (Mar 21, 2012)

Antenna + base = 3'2"
The rod itself is 33.5"
The coax all the way from the base to the end of the connector is about 15'5"


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## 431unknown (Mar 21, 2012)

So total it's around 18.5 feet  or so ,that's acceptable. If you have a multimeter check continuity of the coax and antenna for shorts. Link if needed.

When I was a teenager I had burnt out a CB once because I did not have the radio properly grounded right, I operated the radio while my magnetic whip was laying in the back seat. I can't remember what the symptoms were exactly that caused me to take it to a shop for checking, but they asked me if I had operated it with out having my whip on my roof.  I'm starting to think your radio has suffered a similar fate.

As for the whip I had offered up, I looked and couldn't find it where I thought it should be and really now have know idea where it could be.


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## Sicklyboy (Mar 31, 2012)

Necropost - I am getting no continuity between the pin of the coax connector and the antenna.


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## 431unknown (Apr 5, 2012)

So are you going to go out and buy a new antennae and some coax?


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