Date   : Sun, 04 Oct 1998 16:43:11 +0100
From   : Mike Tomlinson <mike@...>
Subject: Re: HELP ME fix my BBC model B

In message <361629ED.776D@...>, Fun Harbour
<fun.harbour@...> writes

>I know this is probably in the wrong mailing list - but I have a problem
>with my BBC.  It's just decided to stop recognizing  the keyboard.

Try swapping around the user and system VIAs.  These are both 6522s and
are interchangeable.   One is in socket IC3 to the left of the 6502, and
the other is in socket IC69, to the south of the 6502.  The 6522 in IC3
controls the keyboard in addition to performing other system control
tasks and is a fairly common failure point.

Make sure the keyboard ribbon cable is in good condition with no broken
wires.  It can develop bad connections; unplugging it and refitting at
both ends a couple of times usually cures the problem.

Acorn tended to refer to the motherboard of the BBC in north-south-east-
west terms, so working from the 6502, which is in the centre of the
board, the system 6522 and floppy disc interfaces are to the west, the
SAA5050 teletext chip and RAM are to the east, the 6845 video chip is to
the north, and the user 6522 VIA is to the south.

Hope that was useful - a bit of useless information to brighten your
day...


-- 
Mike Tomlinson
See the sci.electronics.repair FAQ mirror at  
http://www.jasper.demon.co.uk/repairfaq/