Date   : Wed, 01 Nov 2006 11:19:47 -0600
From   : julesrichardsonuk@... (Jules Richardson)
Subject: Dead Beebs

Alex Taylor wrote:
> I have a load in bits and I'm starting to forget what's wrong with 
> them all.

If I've got a pile of similar stuff like that I tend to slap disk labels on 
the underside of each with a few scribbled notes on - but then I've got a 
surplus of disk labels and I need to use them for *something* :-)

(actually most of my beebs have labels on the underside with notes about 
what's inside them, to save me plugging them in to find out each time I'm 
after something specific)

> I have three or four that just emit the initial startup tone but don't 
> get to the beep. I'm sure I've seen a fault-finding guide for this but 
> can't find anything - does anyone have any pointers?

Probably the one on Sprow's website: 
http://www.sprow.co.uk/bbc/doctor.htm#justcursor

> I've got one that crashes with a corrupt screen if it's been on for a 
> while. I've swapped the Video ULA and the 6502 with no difference, and 
> nothing seems to be excessively hot. Could this be bad RAM, and how do I 
> find which chip is bad?

Hmm, typically a dead DRAM chip will run noticably hotter than others, but you 
say that's not the case here. A can of freezer spray might be worth a try - 
squirt each chip in turn and reboot to see if there's one particular culprit. 
Maybe it's not hotter to the touch, but the freezer spray will show up which 
one it is.

Could also be a related fault (address decoding ICs and related bus buffers 
etc.), but RAM is much more likely I would think.

Without looking at the manual, I can't remember if you can choose to disable 
one 16K bank of memory (i.e. it may be that the jumpers can only disable the 
same bank) as that could help rule out a memory fault (or otherwise).

cheers

Jules