Date   : Sat, 12 Mar 2016 00:01:26 +0000 (WET)
From   : bbcmicro@... (Peter Coghlan)
Subject: Soldering iron and use

>
> Have picked up a couple of dead BBC B computers and looking to have a go at
> replacing the PSU capacitors.
>

The capacitors that fail in the BBC B PSUs are the mains filter capacitors.
These emit large quantities of smoke but they don't usually cause the machine
to stop working.  If the machines are dead, there is probably a different
cause.
 
>
> Now I haven't soldered in a very long time and apart from looking at YouTube
> (any training recommendations welcomed) I'm also looking around for a
> reasonable soldering iron.
>

I would suggest practicing desoldering and resoldering components on some old
boards that are of no further use before trying a repair on a salvagable board.

It is important to have the have the items to be soldered bright and shiney.
Use sandpaper or a fine file to clean leads which have become dull, tarnished
or dirty.  Use the iron to heat the component and track first, then apply the
solder to the point where they meet.

When desoldering, applying a small amount of new solder to the joint first
can make it easier to melt the joint.
 
>
> Some people recommend gas as you don't have the trailing lead. I do have an
> old electric one that's quite discoloured, although does seem able to tin
> wires etc ok. Not sure about fine work.
>

I used a gas soldering iron for a while but I gave it up when it started to
leak and I found I had to fill it before every job.
 
>
> I was also rubbish at spotting dry joints, another perennial PCB issue, so
> again any tips welcome!
>

They look dull instead of shiney.  Wiggle the component and you may see the
lead move inside the joint.

Regards,
Peter Coghlan.