Date   : Sun, 22 Apr 2012 00:11:50 +0100 (WET-DST)
From   : BBCMICRO@... (Peter Coghlan)
Subject: Video Problems

>
>VDU 7 and PRINT CHR$(7) both make the beep, as they should. It beeps after a 
>CTRL-BREAK too.
>

Strange that those work but the beep at startup doesn't.

>
>MODE7:!&7C01=-1 moves the cursor to the top left, like CLS
>
>Also discovered that leaving it on for a while makes loads of rubbish 
>(mostly long horizontal white lines) appear on screen (as a chip gets hot?)
>
>And replacing the CRTC does nothing
>

Hmmm. It's beginning to look like one of those "could be anything" kind of
faults.

First thing to do is to make sure the +5V power supply voltage is good.

Next, my usual approach would be to try to remove all the non-essentials and
hope that one of them is causing the problem and that it then clears up.
However, this is not guaranteed to help - whatever is causing it could be
essential!

You could try removing the user VIA, the ADC, the serial ULA (if not soldered)
and any extra paged ROMs (except BASIC). It would also be nice to remove the
disk controller but this can result in causing the machine to hang if jumper
S9 is not replaced when the chip is out. While the user VIA is out, you could
swap it in for the system VIA in case that is misbehaving.

You could also try chaning the 16K/32K jumper S25 to see if that makes
any difference. Leaving the jumper out altogether may also be worth trying as
I vaguely recall someone saying that this causes the opposite bank of 16K to be
used.

Regards,
Peter Coghlan.