Date   : Sun, 30 Jun 1996 19:19:55
From   : pnt103@...
Subject: Re: Hardware problems

Hi, all.

Jules has suggested breaking the chip rather than using a solder-sucker.
I wouldn't even contemplate trying his suggestion in the way he described it.
There's a real risk of ripping a plated-through-hole completely out of the
PCB before the chip cracks, and every likelihood of damaging any tracks that
run under the chip.

A decent standard-sized solder-sucker and a good soldering iron should do the
job; don't use a miniature solder sucker, and don't use one of those dinky
little miniature 15W irons -- they don't have enough heat capacity.  It may
well help to apply a little fresh solder to the joints first (the new flux
helps clean up the joint and make the solder run better).  I find it helps
to flick the desoldered pin with a fingernail (from the underside) or poke
it with a small screwdriver (on the component side), in order to break the
last little solder bridge after using the sucker.

If that doesn't help, a trick often used by the pros, is to cut each leg,
as close to the board as possible, with a very fine pair of cutters. 
Remove the body of the chip, and desolder the remaining stubs of pins, from
the top (component) side of the PCB.

Jules' suggestion about using a socket for the replacement is sound, though.
Every time a PCB is attacked with a soldering iron, the glue holding the
copper to the board is weakened.  Fitting a socket prevents this happening
too often in the same spot -- and hence prevents tracks lifting "the next
time".

Beeb boards are mostly pretty well made, much better than some American
PCBs I've worked on.  If you feel reasonably confident, give it a try.

I've no idea what the brown muck might be; if it was everywhere, I'd suggest
it might be tobacco tar if the machine was used in a smoky atmosphere.
Chocolate, perhaps?  I've found far odder things inside computers. Just 
clean it off...

BTW, if you've got the soldering iron out anyway, look closely at the joints
round the RAM and stuff.  It won't hurt to re-make any joint that looks 
badly oxidised, crystalline, or hasn't much solder on it.  Maybe you have a
dry joint.  There might even be a broken socket somewhere (if a pin comes
loose -- or falls out, or flops over -- when you resolder a joint, it was
bust.  Not uncommon.).

Pete