reverse polarity diodes

frogman296 · Post by **frogman296** » Wednesday 13th Aug 2008, 5:37

this, lil question, basically applies to the cobra/uniden 40 channel cbs. i know the whole protection principle must be very similar in most cbs.

i have seen these radios that have been hooked up incorrectly, resulting in a blown reverse polarity diode.....some just cut the diode and fire the radio back up...

IF....one were to hook the radio up incorrectly again with the diode cut, what would be harmed?? the transformers??

thanks in advance for, hopefully, a lil lesson.

frogman

ramblingman · Post by **ramblingman** » Wednesday 13th Aug 2008, 12:12

It could possibily burn out anything that is on the 13.8 volt line.
Audio chip,Although ive seen these go even with the diode in series.
Final,driver.Sometimes it will burn out the transformer to.
Also it will most assuredly burn out some foil traces. Especially
around were the power wires and diode area. And the traces going
to the on/off switch.They are to cheap,not to go ahead and just
change them out.I always go ahead and change it out.It is a easy fix.
Only take a couple on minutes to change out.Most any of the
1n4000 series diode will work.I generally use the 1n4002/1n4003
And like i say they are really cheap diodes.You can get a pack with
several in it at rat shack,for a couple bucks.To cheap and too easy
of a fix,to take a chance on fried parts all over the board.I have seen
radios were people just clip out the protection diode,and on top of
that wrap the damn fuse in foil.What a mess.

timrim · Post by **timrim** » Wednesday 13th Aug 2008, 12:19

It will be a mess if hooked up backwards without the diode. When hooked up backwards, the diode immediately shorts and protects the rest of the radio from damage. I personally have seen blown finals, audio chips, electrolytic caps blown to smitherines, voltage regulators etc. Its never a good idea to use the radio without it.

frogman296 · Post by **frogman296** » Wednesday 13th Aug 2008, 23:52

just curious....i replace em all the time....but i had one here that somebody had clipped the diode, and a fella hooked it up wrong...

thanks for the info

frogman296 · Post by **frogman296** » Thursday 14th Aug 2008, 5:21

well...a fella had dropped off 3 radios...to be repaired...he said they just wouldn't turn on at all...so i checked em, replaced the diodes in them except the one with the clipped diode(what inspired this topic).

i asked him if he had hooked em up backwards, he said that he hadn't but said when he was connecting the coaxial it was sparking...i knew something was awry, so i checked the wires today with the vom...sure enough...there was a small bit of voltage coming in through the negative of the power cord.

i have no idea how this happened...but..a new ground and voila..

thanks fellas