Date   : Wed, 16 Sep 2009 23:47:07 +0100
From   : philpem@... (Philip Pemberton)
Subject: No longer Mouldy Beebs

Phil Blundell wrote:
> That's the later (VLSI-sourced) VIDPROC.  Those ones shouldn't need a
> heatsink, although it's normal for them to run a bit warm: Chris is
> correct that it's only the Ferranti ones that need extra cooling to work
> properly.

For anyone who's interested, the key to identifying them is the logo.

VLSI used two logos --
   * a "V" made up of diagonal lines in a filled circle (this was the 
later logo). Typically seen on the IOMD chips in RiscPCs, and the 
MEMC/IOC chips in Archimedes-class machines. Also (rarely) seen on BBC gear.
   * the "VTi" logo shown in vidproc.jpg -- made up of filled blocks and 
horizontal lines. This being the earlier of the two logos. Typically 
seen on just about any non-74LS chip in a Master, or the ULAs and 
(possibly) disc controller in a BBC B.

Ferranti chips are usually marked "FERRANTI ULA", but if the Ferranti 
text is missing, look for a symbol that looks like a diode, vertically 
aligned (anode at the top, cathode line horizontal at the bottom), with 
a sinewave overlaid on the anode wire.

"Once seen, never forgotten."

... of course, if it's got a heatsink on it, there's a >99.8% chance 
it's a Ferranti, unless someone's upgraded it and kept the heatsink for 
posterity (aka "for the sheer hell of it"). If you have cause to remove 
the heatsink, it can be done with a beaker of isopropyl and a 
screwdriver. Leave the chip to soak for a bit, then push the screwdriver 
in between the heatsink and the body of the chip.

This, of course, assumes the chip is duff and you need the heatsink for 
a replacement you found somewhere...

-- 
Phil.
philpem@...          
http://www.philpem.me.uk/