Date   : Sat, 21 Apr 2012 21:59:47 +0100 (WET-DST)
From   : BBCMICRO@... (Peter Coghlan)
Subject: Video Problems

>
>After taking the board out completely and looking at the solder side, 
>there's a wire link soldered between pin 8 of IC30 and pin 10 of IC25. 
>There's also a track cut beneath IC25 (but not connected to IC25), any idea 
>what that's for?
>

IC25 generates the enable signal for IC14, the bus tranceiver which passes data
between the main data bus and the memory and video data bus. According to my
circuit diagram, pin 10 of IC25 is normally driven by pin 11 of IC29.
Hopefully, the track you saw cut isolates those two pins, otherwise pin 11 of
IC29 which is an output would fight with pin 8 of IC30 which is also an output.
IC30 is part of the clock generator circuit. I don't know what the effect of
these modifications is.

Regards,
Peter Coghlan.