Date   : Tue, 18 Nov 1997 14:31:31 +0000
From   : David.Parkin@...
Subject: Hello and BBC B Hardware faults

I have recently become the proud owner of a BBC B which I was
lucky enough to inherit when a former employer was about to
throw it out.

Having learnt to program on one during the early '80s when I
was nowt-but-a-lad I was keen to renew the acquaintance and I have
to say that although the speed leaves something to be desired the
ease of use and flexibility is just as good as I remember.

Anyway, being rather old this beeb has a couple of hardware 'faults'
which I would like to fix if possible.

Given time I'm sure I can track both of these down, but for all I know
they might both be common faults, with well known fixes. If anybody can
offer any advice then now is the time to speak.

Fault 1

Occassional keyboard lock-ups. All keys except BREAK and ESCAPE appear
not to work. If you do a BREAK then you get the standard 'soft' break. If
you do a <CTRL> BREAK then you still get a 'soft' break. So it appears
that the processor is not seeing that the <CTRL> key is down. For some
strange reason <ESCAPE> works fine. Problem seems to resolve itself after
being switched off for a few minutes. (Overheating?)

Fault 2

When using the RGB output the display works fine provided I only fit the
top half of the DIN connector shell. If I fit the bottom half as well
then the output dissappears. An attempt as ASCII art follows...

End-on view of RGB DIN connector with only upper shell fitted

      _________
     /         \               WORKS OK
    /  O  O  O  \
        O   O
          O

End-on view of RGB DIN connector with both shells fitted

      _________
     /         \               DOESN'T WORK
    /  O  O  O  \
    \   O   O   /
     \    O    /
      \_______/

I have ensured that none of the pins are shorting to the lower shell.
Studying the DIN socket on the beeb I can see that when the lower shell
is fitted it makes electrical contact with a small finger which seems to
be connected to ground. But in the cable I have, the shells are not
connected to anything, so I can't see why having the lower shell makes
any difference. Are these sockets in the beeb prone to internal shorts?

Any ideas?

David.Parkin@...