Date   : Fri, 28 Jun 1996 18:14:39
From   : pnt103@...
Subject: Video processors

Steve wrote:

>             If I run with the lid on, it locks up more quickly, say
> two minutes.  If I remove the heat sink from the ULA, it happens almost
> instantly.  Does this indicate that the problem is the ULA overheating? 
> Do I need to get some more of this white gunk to fix the heatsink on
> properly?

Very probably, to both questions.

>> Nitpick: video processors (VTi chips) don't use heatsinks, only the
>> original Ferranti ULAs.
> 
> What's the difference?  Is the VTi better?  One of the spare boards I've
> got appears to have a VTi chip on.  IC6 has "VTi" in fancy lettering, and
> "417 V 2472   VC 2069   201647  (c)Acorn Computer  KOREA-AE".  Should I
> try swapping this for the ULA in my board?

The VTi is a different type of custom chip, which uses less power and
dissipates less heat.  The only advantage is that it doesn't need a heatsink
(actually the only reason the Ferranti ULA needed a heatsink was due to a
small error in the original mask).  However, there were two issues of the
VTi processor.  The earliest ones needed a small modification to S26 (remove
the link, solder a wire from the centre pin to IC10 pin1).

You have the later version, identified by the "VC 2069", which works just 
like the original ULA, so go ahead and try it.

Pete