Date   : Sat, 06 Nov 2010 18:22:53 +0000
From   : zeem.uk@... (Alex Taylor)
Subject: Composite Output Capacitors Gone - Hideous blurring

On 5 November 2010 18:09, Ben Collier <bmcollier@...> wrote:

> I got an old BBC Master as part of a job lot, and aside from the ones which
> are booting up in hi-def mode and telling me that something isn't a
> language, which I will deal with at some point in the future

In case you don't already know, that's caused by the pack of 4
alkaline AA cells going flat, causing the CMOS RAM to lose its
contents. The machine can be made functional without replacing the
batteries, but it will need a series of *INSERT and *CONFIGURE
commands each time it is turned on, in order to restore sane defaults.
An upgrade from MOS 3.1 to MOS 3.5 will make the machine load sane
defaults if the batteries go flat, but without the batteries you won't
be able to customise things such as the startup mode or default filing
system.

> one which is
> working has horrible smearing from the composite/monitor output and the
> colour is totally up the wall.
>
> Which capacitor has gone?? Is it a capacitor? Where can I buy a replacement?

This depends if it's an issue 1 or issue 2 motherboard. The issue 1
requires a capacitor soldered on, monochrome output is the default.
Details of the capacitor have been mentioned in another recent post on
this list. Issue 2 motherboards (IIRC) use a jumper to select colour
or monochrome, implying that the capacitor's already fitted to the
board. I don't know which one it is, although I'd assume it's 470pF
like the one mentioned in regard to fitting to an issue 1. It'll be
somewhere close to the BNC video output socket.

A replacement could be obtained from somewhere like Maplin
Electronics, and will probably cost pence.

-- 
Alex Taylor