Repairing A4000 leaky NiCd damage?

[Steven Hirsch]

On Fri, 2 Jan 2015, Ethan Dicks wrote:

> Has anyone here gone through the process of reparing leaky NiCd damage
> to an A4000 motherboard?  I _thought_ I had removed the battery some
> time ago but puttering around today, I cracked open the case to find
> the battery still there and some damage around U891 (a 74F245) and
> U850 (Bank 3 DIMM socket).  I have washed off the residue but I may
> have to pull a DIMM socket to get access to the vias under it.
>
> I know the general process, but I'm curious if anyone has done this
> specifically to an A4000 board and has any tips.  As I said, I'm
> probably going to have to pull the DIMM socket to get to all the
> damage.

Went through this entire process on my A4000 a couple of years back. In my 
case there was damage to traces underneath several of the adjacent chips 
and the clock chip was dead to boot.  I would suggest soaking the board 
overnight in dilute vinegar in addition to washing, since the alkaline 
crud gets into via holes where washing won't dislodge it.  If traces are 
not already eaten, this may eliminate the need to remove the DIMM sockets.

I ended up removing all the chips in the immdiate vicinity of the battery 
and piecing things back together with 30g wire.  This did include 
threading through a few of the vias.  One random bit of advice:  The 
leaked crud tends to dissolve the solder mask on the circuit board and 
makes hot-air reflow a bit touch and go.  The solder will migrate 
underneath the chip rather than flowing around the legs.  After two 
unsuccesful rounds with the reflow tool (shorted traces underneath) I 
ended up hand-soldering the smaller parts.

At the time I did this work, the Ricoh clock chip was still available from 
Amigakit in the UK.  Unfortunately its function goes beyond simple 
timekeeping.  It has some involvement in the power-up sequence and the 
system won't function with it.  There may be a way to mod around this, but 
I simply replaced the chip.

Steve



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