Vintage Synth Repair

I'm in the middle of repairing a badly damaged poly-61.... i got the  
old battery off the board, but there are many surrounding components  
which look corroded and a few to the point they are damaged. good to  
know about the solder not melting problem as i anticipate what to do  
next. the insideous thing is that the corrosion works its was down  
the traces and components, and in some cases spreads a lot further  
than just the battery area. the analog board is pristine though, and  
i figure this could be my next DIY project... -pc

On Mar 4, 2010, at 9:19 AM, Scott Nordlund wrote:

>> Could you please describe (both for me and for all the people in  
>> the future who will be reading this sequence of postings) exactly  
>> what kind of damage that an old memory battery does to vintage  
>> synthesizers? Thank you.
>
> Specifically the problem involves rechargeable NiCd batteries.  The  
> more common lithium batteries shouldn't cause any trouble (not that  
> I've ever seen, anyway).  Of course ordinary AA batteries can also  
> leak and ruin your day, but these aren't usually mounted on circuit  
> boards.
>
> A few things that use these: Korg Polysix, Poly 61 and Trident,  
> Siel DK 600, DK 700 and Expander, Roland CR-78, Kawai SX210 and  
> SX240, PPG Wave series, Wersi, as well as lots of other old  
> electronics.  Leakage in pinball machines seems to be particularly  
> insidious, I guess because they can sit in storage for a couple  
> decades while the battery works its magic.
>
> Over time the (NaOH or KOH?) electrolyte leaks out, possibly  
> encouraged by the recharging circuit.  Component leads corrode,  
> circuit board traces turn black, solder turns to a powdery gray  
> substance.  The damage can spread to a quite impressive area,  
> though not all of it will need to be repaired.  The solder is  
> especially a pain since it won't melt or allow new solder to  
> adhere.  It can be very difficult to remove without actually  
> drilling out all the vias and holes.