Inverted polarity issue!

[bfi1714]

Hi!
   
  My work's colleague just asked me if I could check for him his two radios that he has on his boat. The radios are a common AM/FM radio and a UFH radio. Times ago, he plugged the battery power cables inverted (he uses a car battery model) and after this event everything stopped working properly. As a form to help him I went to his boat with my electrical clamp meter and check the resistance of the speaker but everything as alright. So I've started to wonder if the problem couldn't be on the radios. We took them from the boat and I just opened the case of the UFH radio, even knowing that I couldn't to much with only a clamp meter. So, as I person that don't have much experience and tools, I'd like to hear from you what could be the most probable problems. I know that it may be easier and chip to tell him to buy new radios, which his is willing to but even though I'm curious to hear from a professional what happens in such scenario as a form to refresh my mind from my old school on electronics.

Thanks and feel free to ask me more

bfi

[Rerouter]

inside you may be lucky and find a fuse and a half melted diode, its not too uncommon to have some kind of negative polarity clamp on marine and automotive radios, or in the better made cheaper units they sometimes neck down a trace to deliberately blow out, (act as a fuse)

if there is no sign of any protection, and no clear sign of damage, 9 times out of 10 its gone for good

(only today i had to deal with auto electricians that where asked to convert an old car to negative chassis, which consisted of them flipping the 2 battery wires and blowing chunks out of the vintage and very painful to restore instrument cluster)

[ttp]

If you can find them, check the fuses.

[Psi]

The fuse/crowbar/polaritydiode is usually located within a few cm of the DC input jack. So that's where i'd start looking.

[bfi1714]

Thank you all for the answers. I'll follow your tips and then I tell you what's going on!

Thanks

[Yago]

On the old stuff I repaired the audio amp chip sometimes went when rev volted too.

[SeanB]

Almost always with this type, but they generally are cheap ones.

[G7PSK]

I had a problem with an inverter that was wrongly connected the 40 amp fuse was blown by the crowbar diode but the mosfets still blew as well.

[SeanB]

Power semiconductors blow faster than any fuse.