Cobra 29LX won't power up

[Boll Weevil]

And I'm almost certain the culprit is a faulty power supply in a mobile.

I was using a different truck than I normally drive and had the cb plugged into the cigarette lighter. Here's what I know:

1.When I put the radio back in my car it immediately blew the fuse in the lighter plug.

2. When using the same plug in my dc power supply at home, the power indicator light on the plug will flash off/on but will work fine with other radios. The radio in question however, will not light up.

3. My cell phone died that same night after being charged in the same receptacle. Fortunately it was an iphone 3gs that I will be updating in August so a $45 (with warranty) used one off ebay fit the bill. I'm still pissed, but it could've been worse.

My questions are what did I break and is it an easy fix for a guy with mediocre soldering skills and limited technical knowledge?

 

[sonoma]

sounds like you shorted the plug when you pushed it into the socket. this will blow the protect diode at the power plug inside the radio.pull the cover off and look on the board right at the power plug and see if the diode is blown. it may just look burned some.

 

[Robb]

Sounds like you need to use a digital voltmeter to test the polarity of that plug.

The 1N4003 diode will cost you between a nickel or a buck depending where you buy it. Take a noobie 45 minutes to find it (its near the power plug on the board) and replace it. The experience gained by making that mistake, fixing it, and put it back together is priceless - lol . . .

 

[Boll Weevil]

sounds like you shorted the plug when you pushed it into the socket. this will blow the protect diode at the power plug inside the radio.pull the cover off and look on the board right at the power plug and see if the diode is blown. it may just look burned some.

Thanks for the quick reply. I'll do that but probably won't get to it until the weekend.

 

[Boll Weevil]

Sounds like you need to use a digital voltmeter to test the polarity of that plug.

The 1N4003 diode will cost you between a nickel or a buck depending where you buy it. Take a noobie 45 minutes to find it (its near the power plug on the board) and replace it.

I successfully replaced a bunch of stuff in my 29 Classic that involved a whole lotta searching so I do have some experience at finding things. I'll bet I can locate that diode in only 42-43 minutes!

The experience gained by making that mistake, fixing it, and put it back together is priceless - lol.

Absolutely. I guess that would explain why I'm not too tore up about this. Thanks for the schematic and additional info.

 

[Robb]

Might also check L201 to make sure it didn't get smoked too . . .

 

[Boll Weevil]

I only had a few minutes to play with it today but it powered up after removing one leg of D23.

I found L201 printed on the board but couldn't figure out which one it was. I hope to spend a few more minutes tomorrow and maybe take a ride to RS.

 

[dx31353]

I only had a few minutes to play with it today but it powered up after removing one leg of D23.

I found L201 printed on the board but couldn't figure out which one it was. I hope to spend a few more minutes tomorrow and maybe take a ride to RS.

Good deal. I picked up a R&R comp tuned 29 a few weeks ago for 10 bucks that would not turn on, and that was all that was wrong with it hear. After that I had my guy clear up a mic gain squeal and align it properly. Now I have a good talking radio with great ears for fifty bucks invested.

Sent from my SCH-I545 using Tapatalk

 

[Robb]

I only had a few minutes to play with it today but it powered up after removing one leg of D23.

I found L201 printed on the board but couldn't figure out which one it was. I hope to spend a few more minutes tomorrow and maybe take a ride to RS.

Cool beans on the fix. Just remember, that unless you replace that blown diode with a replacement, it is vulnerable to major parts damage if it is shorted or reversed again.

L201 is OK if the radio powered up; but I would still look to see if any charring on it was present. It is a 'choke' that keeps the incoming DC clean from noise. When shorted, it heats up like a toaster coil . . .

 

[Boll Weevil]

Cool beans on the fix. Just remember, that unless you replace that blown diode with a replacement, it is vulnerable to major parts damage if it is shorted or reversed again.

Unplugged it and it won't be plugged in until I get a new diode in place. RS has them in stock 4 miles from home for $1.49 ea. As you can see, I'm willing to pay TOP DOLLAR for fast service.

L201 is OK if the radio powered up; but I would still look to see if any charring on it was present. It is a 'choke' that keeps the incoming DC clean from noise. When shorted, it heats up like a toaster coil . . .

Would that be a cylindrical shaped thingy that's kinda suspended in mid-air, in line from the plug into the board? (sorry if my description is too technical).

 

[Robb]

Unplugged it and it won't be plugged in until I get a new diode in place. RS has them in stock 4 miles from home for $1.49 ea. As you can see, I'm willing to pay TOP DOLLAR for fast service.



Would that be a cylindrical shaped thingy that's kinda suspended in mid-air, in line from the plug into the board? (sorry if my description is too technical).

Yup.

 

[longhaireddwb]

Just be sure to get that diode replaced. I cant tell you how many radios I've seen where people cut the leg on the protection diode and forget about it then they come to me and say they let the magic smoke out. I find a trace on the board burned in half along with a couple other parts toasted.

Dont forget!

 

[Boll Weevil]

Yup.

I thought it looked a bit discolored, but that appears to be wax. It's hard to see but the jumper coming down from the plug has what I think is a slight oxidation where it goes into the top.

 

[Boll Weevil]

Just be sure to get that diode replaced. I cant tell you how many radios I've seen where people cut the leg on the protection diode and forget about it then they come to me and say they let the magic smoke out. I find a trace on the board burned in half along with a couple other parts toasted.

Dont forget!

Nope, ain't gonna happen.

Radio is unplugged and the covers are off. No power until it's back together.

 

[Boll Weevil]

It's up and running again, like nothing ever happened. As an added bonus, the $1.49 Radio Shack price for the 1N4003 was for a 2-pack.

Thanks again, gentlemen!