Date   : Sun, 05 Jun 2011 15:56:16 +1030
From   : station240@... (paul aslin)
Subject: Model B with video corruption

I've swapped IC 55 for a replacement stolen out of another machine, that
fixed the memory problems. While I was trying to replace the other missing
chips the continuous tone fault showed out, then the PSU carked it.

Out of the two model B's, both have dead PSUs now. Fuse blow, X2 caps removed
without fixing short. So looks like a trip to the store to get more spare
parts, before I can get any further.
 

From: station240@...
Date: Sat, 4 Jun 2011 01:19:50 +0930
CC: bbc-micro@...
Subject: Re: [BBC-Micro] Model B with video corruption


Wrote this little program up to find it.
10 cls20 for I=&3000 to &800030 a=?I: if a>0 then print a;" ";I40 next
It's not perfect but found 4 to be the random value, which means D2 is the
bad data line, hence fault in IC 55
IC 55 is slighty warmer than the other RAM chips.
On 03/06/2011,@10:34 PM, "Mark Haysman" <jumbos.bazzar@...>
wrote:



Could be other faults as well, but that screen noise is 
almost definately a bad memory chip, just need to do some pokes and peeks to the 
CAS1 memory range to find what one it is.
 
Mark.





  ----- Original Message ----- 
  From: 
  paul 
  aslin 
  To: bbc-micro@... 
  

> Is the contents of the screen memory
> wrong or is it 
  only what is on the screen that is wrong? If the screen memory
> is 
  corrupt, is non-screen memory corrupt too? Is there corruption in all
> 
  screen modes?

I don't think its the memory itself, noise is rather odd 
  to say the 
  least.
http://s1092.photobucket.com/albums/i405/station240/bad%20B%20video/
View 
  from 1 to 5.jpg and that is the order the noise appears in.
Of note is this 
  is a 20k screen mode, and the top potion is never corrupted. By my 
  calculations this is &3000-&3FFF. Something screwy going on with the 
  addressing.


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