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Uniden 520 Modulation

Received pro-520 XL today. I got it off of Ebay for 50.00.
It is the model that was made in the Philipines. The board is different that the Schematic that is on CBtricks site. This is probably an older model. It works good but the Modulation is low, only about 60 %. Does anyone have the Schematic for the older models? The Modulation limiter circuit is not the D14, etc as on the cbtricks site. If you know the diode and the resistor in series with it that is the feedback circuit I would appreciate it.
Thanks,
 
I was just told by Uniden that the schematic for this model was still not published.
It is the Pro520XL with the black face. Does anyone have this Schematic?
I have the 520e model print from CBtricks but this one is different.

I'll be gone for a few days so I won't be checking for awhile.

Thanks,
 
SOUNDS LIKE YOU GOT ONE OF THE NEWER MODELS THERE HARDHEAD ? ....WHAT YOU ARE LOOKING FOR WOULD BE ON THE BOTTOM SIDE OF THE BOARD IN WHAT (IF I RECALL ?) A SURFACE MOUNT DIODE. IF I WAS YOU ,I WOULD CERTAINLY MAKE SURE YOU KNEW WHICH ONE BEFORE YOU DID ANYTHING. I HAD ONE OF THOSE A FEW YEARS BACK BUT WITHOUT ONE IN FRONT OF ME IT MAKES IT HARD FOR ME TO BE CERTAIN.
 
Wish I would have hung on to mine, I sold a mint one on Egay a few months back all ready P+T with mic and bracket for $10.00....It wasnt worth the effort to take it to the P.O..
Still all and all a goord little radio...
 
Switch Kit said:
SOUNDS LIKE YOU GOT ONE OF THE NEWER MODELS THERE HARDHEAD ? ....WHAT YOU ARE LOOKING FOR WOULD BE ON THE BOTTOM SIDE OF THE BOARD IN WHAT (IF I RECALL ?) A SURFACE MOUNT DIODE. IF I WAS YOU ,I WOULD CERTAINLY MAKE SURE YOU KNEW WHICH ONE BEFORE YOU DID ANYTHING. I HAD ONE OF THOSE A FEW YEARS BACK BUT WITHOUT ONE IN FRONT OF ME IT MAKES IT HARD FOR ME TO BE CERTAIN.
Click to expand...

Thanks, Switch Kit. I appreciate the help. I'm going to run it like it is in the truck. When I get back next week I'll look into it more.
Thanks to all. If anyone should find a schematic for the new ones let me know.

Thanks,
 
Re: uniden 520

351_bear said:
the diode is d 203 clip it thats for some of the 520's
Click to expand...

The problem is they are not labeled and there is no schematic
or board layout published that i can find. Thanks for the info
I will continue to try to fing a print. I don't want to clip it I would
rather adjust the resistance value of the circuit to up the modulation.
 
I realy do wonder why you would bother to do a "mod" on a CB radio, even with your mod they are next to useless, other than close comms in convoy or say on a farm. No guys and girls, i'm not knocking you , if you like it ,do it, but i would like you to tell me what benefits you get out of doing these mods. Perhaps i have missed something good , but i have found all cb radio to be useless and that includes uhf repeater stations that claim to extend over 100Klm I realy would like to chat about this, and would love to hear from guys and girls. The equipment i use is CODAN 8525B with 400 channel auto tune antenna. It has been "altered" to put out about 140 watts PEP...at night it covers all of Australia( east coast to west coast is about 3600 miles..south coast to north coast is 2500 miles) and i can chat to all the Royal Flying Doctor Service bases throughout Australia . i do hope we will chat FLYINGFOX@PEOPLE.NET.AU
WARM GREETINGS TO ALL AND STAY SAFE AND WELL!! DENNIS
 
Hello Hardhead, i can understand your frustration with getting the circuit diagram for your UNIDEN PRO 520XL. mine too was made in the phillipines and i am also unable to get a circuit diagram. if the set you have just received has any TX RX audio out problems
replace the 2sc2166 rf transister mounted on the back of the case, this little guy seems to ware more than one hat, I.E. it seems to do audio, tx & rx it seems this (mine) transister goes leaky and pull the set down into low tx low rx and will upset the audio
out quality..CAUTION !! the front panel mike socket is very rigid and if it comes loose it will break the fine tracks on the front panel circuit board and is a bugger to repair. I now
know that this problem is known to others . Should you like to chat about this set why not email me WARM GREETINGS DENNIS flyingfox@people.net.au
 
Hardhead said:
How do you turn up the Mod on the 520?
Q6 is the AMC but there is no variable control. Which component do I change to increase the Mod with out over Modulating?
Any help is appreciated.
I checked on CBTRicks and DTB's site but there was no help.
:?:
Click to expand...

It's hard to believe a slug radio like the 520 will overmodulate no matter how you hack and rape it.
 
psycho said:
It's hard to believe a slug radio like the 520 will overmodulate no matter how you hack and rape it.
Click to expand...

They are a great sounding AM radio when tuned up right and it doesn't take much to do it. They don't put out a lot of power, but that's easily fixed.

I ran a 520XL with a TS-250 for years and it was great.
 
most of the ones i done on the newer ones was d201 there was a string of red diodes by the audio xformer to the left with the bottom off and the radio facing you it is lik the 2nd or 3rd in string labled on board
 
" I realy do wonder why you would bother to do a "mod" on a CB radio, even with your mod they are next to useless, "

I would say I totally disagree with this statement. A properly tuned and aligned radio sounds and performs much better then a ballparked in assembly line tune. Here in the USA we have this government agency called the FCC. So a stock radio is 4 watts with maybe 60% modulation. Just getting a radio on frequency and boosting modulation to 100% is well worth the effort.
 
Help Uniden Pro 520XL

Hey guys just wanting to find out how i can fix my radio as it is doing weird things when TX'ing. i can hear good used the PA function and it works good and sounds good. but when i TX it is all distorted. does anyone know what i can do to fix that?
Cheers
Josh
 

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