Uniden Pro 510xl Killed By NooB

[Gashog]

I reversed polarity and killed my radio.
I replaced the idiot diode (which was dead shorted) and it powers up, but won't Rx or Tx and makes only very faint static through the speaker.
Would anyone here be willing to walk me through diaging and fixing my radio?
I feel like a complete idiot and I'd really like to correct this mistake.

 

[Robb]

No; that is the 'mistake diode'. If you happen to make the same mistake twice in a row; then it is the 'idiot diode'.

That diode is there to keep the circuit from getting fried. Never had any problem replacing the diode and then having any radio issues afterwards.

Unless of course you left out the mistake diode and then powered it up w/o correcting the power wires first. If that is the case, then there is a lot of component damage and probably not worth fixing.

 

[Gashog]

The fuse is a 20A or 30A and didn't blow.
I'd really like to fix the radio, even though I could just get another one.
The eyebrow board and display are fine and the main board isn't burned anywhere.
I'm pretty sure I'm 1 or two components away from a working radio.
I know it's silly but I screwed up a perfectly good radio and I'm having a hard time letting it go.

 

[2RT307]

The fuse is a 20A or 30A and didn't blow.
I'd really like to fix the radio, even though I could just get another one.
The eyebrow board and display are fine and the main board isn't burned anywhere.
I'm pretty sure I'm 1 or two components away from a working radio.
I know it's silly but I screwed up a perfectly good radio and I'm having a hard time letting it go.

20 or 30 amps? For real? It should only be about 3 amps max. If it's 20 or 30, no wonder it didn't blow.

73,
Brett

 

[Gashog]

20 or 30 amps? For real? It should only be about 3 amps max. If it's 20 or 30, no wonder it didn't blow.

73,
Brett

Yup it's a regular automotive buss fuse. I can't make out the amperage but it's heavy.
I need to fix this radio to erase my failure at patience and common sense.
The only thing wrong with it was the mic cord. I cut it back and resoldered it, plugged it back in and accidentally got the power and ground wires crossed up when I went to bench test the radio.
Stupid mistake....not taking a second to make sure I had the polarity correct.
I tested the mic on a 29 and it works fine.

 

[Robb]

30A fuse?!?
Audio chip, VCO, PLL, and final.
>poof<

 

[Gashog]

30A fuse?!?
Audio chip, VCO, PLL, and final.
>poof<

SO basically every IC on the main board.
Maybe I'll look for one with a bad segmented LED or banged up face.

 

[Robb]

If that board had reverse voltage put to it with no protection diode to stop it, then any parts that uses a silicon junction would have to have been fried . . .

A fuse - a proper sized one - is there to stop too much current flow to the board. It heats up rapidly and opens up when the draw limit has been reached.

You can test those parts to see if they are still good before you decide to give it the deep six . . .

 

[Captain Kilowatt]

Holy sweet mother of God what was a 20 or 30 amp fuse doing in the power leads other than "not much". The wiring resistance limited the current flow during the reverse polarity hook-up and that is why the fuse didn't blow.

Rule #1--ALWAYS use a fuse in the power leads.

Rule #2--ALWAYS use an appropriate rated fuse. In this case 2 or preferably 3 amps.

I refuse to work on radios that were hooked up backwards and the few that I ever did that had no fuse or grossly over rated fuse were garbage.

 

[loosecannon]

first of all, i love the title of this thread! LOL

gashog, it seems that my compatriots have sufficiently slapped you around for using the wrong size fuse, so i will not attempt further slappage.

you say that the radio will turn on, and it sounds like the channel display lights up.
is that right?

if so, there is a chance that you can repair this radio with one part change.

if this doesn't work however, you have just acquired your first parts radio.

if this radio is similar to the 510e, then you should have a 7808 regulator transistor in there somewhere.

i'll attach a picture of one so you'll know what they look like.
there will be at least one more transistor in the radio that looks like it, so be sure you found the one that says 7808 on the front of it.

this is the main 8 volt regulator in the radio, and pretty much nothing will work if it goes bad.

so, once you find it, we will test it.
they are simple. they have an input leg (left leg if you are looking at the front of the transistor) a ground leg (middle), and an output leg (right side if you are looking at the front)

the input leg takes its voltage from the main supply, which is 13.8 volts, and the output leg puts out a regulated 8 volts to power various circuits in the radio.

why is this part needed? because even if the supply voltage drops down to 11 volts or so; the regulator will still put out the regulated 8 volts.

found it yet?
good.
now to test it.

get out your DC volt meter and connect the negative lead to the ground connection on the power jack.
turn the radio on, and put the positive lead on one of the outside legs of the 7808.
if you picked the input leg, you will see the input voltage here, which is usually around 13.8 volts.
if you read the middle leg, you will get 0 volts because it is also grounded.

now read the other outside leg. if the other side was the input, then this leg should read 8 volts.
if it does not, then replace it.

if it does read 8 volts steady, then you are screwed and have a bigger problem than we can guide you through here.

so again, measure the outside legs of the 7808. one side should read 13.8 volts (radio on!) and the other side should read 8 volts.

if it's bad, you can get one at radio shack if there is one open near you, or you can order one off of ebay for a couple of bucks.

best of luck!
LC

 

[Robb]

Slapping him around wasn't my point. Poor guy lost his radio, and that is just sad. I hope I answered his questions sufficiently. Like I said in the first place, it is a mistake diode. Not an idiot diode . . .

 

[loosecannon]

I was just trying to be funny there Robb.

judging by the thread's title, i figured gashog had a pretty good sense of humor.

lots of burned radios due to oversized fuses these days!
LC

 

[Gashog]

First, thank you to everyone who has posted.
In the interest of TLDR I'll keep it short.
I asked this question on another forum.....we'll call it http://www.cbradiotalk.com/index.php
And although they seem like a nice bunch over there, I have to wait a day or so before my posts are approved because....ya know....I might be a malicious robot!

Second, intro:
I'm a middle aged guy who doesn't make much money.
I have a few hobbies but learning is my one main one.

About the radio;
I spared everyone the back story initially but, here it is.
I picked up a Cobra 29 circa 1993, the 510 and a couple whips (one magnetic Wilson and one mirror mount GE) for $20.
The Cobra, I managed to power up and transmit/receive without releasing the magic smoke.

I want to try to fix the 510 and I'm grateful to everyone for their input.

Incidentally the fuse was installed probably some time around Desert Storm, judging by the patina.
My fault for not checking for boobie traps before putting a battery to it.

I'll report back after work.

 

[Captain Kilowatt]

Loosecannon has the idea about the 7808 regulator but if that does not work the radio is indeed most likely toast. It doesn't take long for repairs to cost more than the radio if you need a shop to work on it. Often more than one part is damaged and replacing one when you find it can cause it to blow again because of other bad parts.

 

[2RT307]

On the upside, at least this was a very inexpensive radio. Trust me, I've made more expensive mistakes. Poofing the transistors in a neat little 100 watt base amp from too much power input always comes to mind. And that awful smell that was in the room.

73,
Brett