A Chemistry question for those that know about chemistry.

[ProDave]

This week I have been getting our touring caravan ready for the season.  First job was fix the battery charger / monitor / control system that had died over winter.  Simple and boringly monotonous electrolytic capacitor failure.  that is not the question.

 

Now the 12V electrics will turn on I find the car radio is dead.  Withdrawing it from it's slot and a small amount of rusty brown coloured water dripped out.  It seems the water has entered a leak at the roof mounted aerial and ran down the inside of the coax and entered the radio through the aerial plug.

 

Inside the radio there was an area of dried up rusty water on the PCB.  When I cleaned it off, it revealed that several of the tracks were missing, simply gone.

 

Water won't dissolve copper.  So I am wondering what compound has been created here that did dissolve the copper?

 

I know Ferric Chloride is the normal chemical for dissolving copper.  Is that what has been created by rainwater running down inside a coax cable and then rusting the steel aerial plug on the end of the cable?  Or what other compound may have been made that dissolves copper?

[ToughButterCup]

1 hour ago, ProDave said:

.....  Or what other compound may have been made that dissolves copper?

 

Nitric and  sulphuric acids - from memory - will dissolve copper (Got kicked out of the Chemistry class before 'O' Level because I threw a snowball at the Chemistry teachers car). 

Nitric is unlikely to have been made, that leaves sulphuric. Where does the sulphur come from? 

Maybe a hen laid an egg in the dashboard , that eggshell rotted a bit and then  got a bit of water on it - that created a bit of sulphur - the sulphur plus a bit more water then corroded the terminal

 

.... BINGO - that's wot did it Dave.  

Medals, medals, I want a medal. 

Please.

[SteamyTea]

The PCB was probably printed, rather than etched. So could be part of that processes that has dissolved.

[ProDave]

49 minutes ago, SteamyTea said:

The PCB was probably printed, rather than etched. So could be part of that processes that has dissolved.

But the copper has GONE.  Not just lifted from the board, gone, dissolved, no longer present.

 

Regardless of how the board was made, something has dissolved the copper.  I have never seen that before 

[Alan Ambrose]

Leaking electrolytics will do that too. If you like working on small things you can (a) clean the board with IPA, (b) solder on little jumper wires after carefully scraping the soldermask off the bit you want to solder. Magnification of some sort helps a lot.

[ProDave]

I have so far replaced one clearly missing track with a wire link, and put wire links through 2 via's that were no linger making continuity through.  But still is is resolutely totally dead.

 

I have just downloaded the service manual that contains the circuit diagrams and the board layouts, so there might be a chance of resurrecting it.

[Alan Ambrose]

Ah, you're one link away from success 

[SteamyTea]

47 minutes ago, Alan Ambrose said:

Ah, you're one link away from success

Two if you don't know the security code.