BBC-B Power Supply Repair

So there you are, your BBC-B is sat beside you loading in ELITE from tape.
You are merrily surfing the net whilst waiting for this on the next bench over.
You hear a sound like someone screwing up a crisp packet followed by a strange hiss!
A quick glance over and your Beeb is erupting acrid white smoke from every vent.
ELITE is still loading fine as I dive for the mains switch to cut the power.

No panic as in the world of Beeb's I have been there and done it before.
Just that when it happens at 9pm with all the ventilation in the world you know
that your going to be smelling that mess all through the night.

Anyway, its caused usually by C2 in the power supply going fizz-pop so strip the
machine down, get the PSU out. Wrestle with getting the PCB out of the chassis for
about 15mins then take a look at the charred remains of the CAP.

fizz1.JPG - 185Kb
So here we are greeted with a very sorry looking C2, a 100uf Capacitor with its guts hanging out!
Oh, and did I mention the Stink?

fizz2.JPG - 210Kb
Get the Iron on and whip it out!

fizz3.JPG - 181Kb
Luckily I had a brand new spare in my box of electrickery goodies.
The new one is of equivalent rating, 100nf instead of 1uf, all the same.

Re-assembled the PSU, put the Beeb back together and switch on and pray!
No drama's, it did not go boom or fizz and is now back to working perfectly.

This is a common fault well documented elswhere on the net so I wont go into the
technical details all over, but all Beeb's getting to this age will have these cap's
in a very stressed state and will need replacing. So don't worry if your newly aquired
or newly rescued out of storage Beeb goes crackle-fizz. It's all repairable and will
only take up about 30-45 mins of work when you get the hang of it :-)
(well thats what us regulars take after many a smoking Beeb adventure).

If you have arrived here from a Search Engine
Click the link below to go to the Classic Acorn Home Page
Everyone else use the Navigation Section on the Left