Cobra 29 LX blowing fuses

[Big_D]

I picked up a 29 lx that blows the fuse when you hook it up. I checked the polarity protection diode and it looks fine. What else should I look at?

 

[Robb]

I'd look a lot closer at that diode; see if it is split/cracked anywhere.
I'd still replace it to be sure that wasn't it.

After that, you will have to look at the schematic and find/disconnect all solid state devices that are on the mains 12v rail. Such as the audio chip, voltage reg, etc. Then, hook them up one at a time and try turning it on. Also IIRC suspect the zener diode on the regulator circuit too.

 

[Big_D]

I clipped one leg off of it and when I check continuity between the power and ground prongs its still shorted

 

[sonoma]

did you clip d23? make sure that is the one you clipped. did you try power to the radio after clipping it. you said you show continuity which you will still have some when using a ohm meter to check the power leads. here is then schematic for the 29LX radio.

http://downloads.cobra.com/CB/Models/29-SERIES/29_LX/29LX_schematic.pdf

 

[999]

Check continuity on the diode in both directions with it out of circuit. If you get a beep both directions, there is your culprit.

 

[kopcicle]

Cobra 29 LX blowing fuses


If it's getting paid it's regulated in most states if not illegal.

If it's mutual consent and not for profit , what business is it of yours?

 

[Handy Andy]

I picked up a 29 lx that blows the fuse when you hook it up. I checked the polarity protection diode and it looks fine. What else should I look at?

Condition of components...

Burnt parts, look for blown parts or discoloration, use your nose to detect scent of Kingsford, or "burnt Skunk" are good clues...

Take both clamshells off and observe traces for scorch marks or melted / welded parts - even look at the Clamshells themselves - their insides - look for traces of smoke or burn from pop welds.

The radio may have been part of a more catastrophic failure either by assembly or when assembled - the case got warped and shorted to the foil traces inside - this can happen and the radio looks normal but may have got pressed too hard together and now you have a radio with several parts blown and shorted out due to it.

 

[TheRealPorkchop]

Cobra 29 LX blowing fuses


If it's getting paid it's regulated in most states if not illegal.

If it's mutual consent and not for profit , what business is it of yours?

That’s twisted and demented but funny AF.

 

[Big_D]

did you clip d23? make sure that is the one you clipped. did you try power to the radio after clipping it. you said you show continuity which you will still have some when using a ohm meter to check the power leads. here is then schematic for the 29LX radio.

http://downloads.cobra.com/CB/Models/29-SERIES/29_LX/29LX_schematic.pdf

I clipped d26 I believe. That's what I read some where on google.

 

[sonoma]

the schematic shows it to be D23 a 1n4003 diode.

 

[Big_D]

I finally found it. Clipped it and there is no longer continuity between positive and negative posts

 

[Robb]

I finally found it. Clipped it and there is no longer continuity between positive and negative posts

Please don't forget to replace it. It serves a purpose - saving all of the silicon devices from being shorted out. Cheap protection @ $.05/ea.

 

[Big_D]

Definitely going to replace it. I just wanted to be sure what the issue was before spending money on it. I hooked it up after checking for continuity and it seems to work like it should.

 

[sonoma]

glad you found it. be sure to solder the other one you cut earlier. as Robb stated be sure to replace it.

 

[Big_D]

I soldered the one that I cut before I ever tried to power it. I appreciate all of the help.