Date   : Sat, 30 Oct 1999 13:54:38 +0200
From   : "Mark Usher" <marku@...>
Subject: Re: Further investigation 

> Is the 8271 itself a known good part?
yes.
 
> Could be, though there are other possible causes too.  What 
> exactly do you 
> see at IC94 pins 4, 5 and 12, and at IC91 pin 8?
These values are from an anologue display and so are approx.

              bad bbc    good bbc
ic94 pin4  =     2v        2v
ic94 pin5  =  1.75v       1.75v
ic94 pin12 =     5v          wave 5v

ic91 pin 4 =     5v         5v 
ic91 pin 5 =    .4v         5v
ic91 pin 6 =    .4v        .2v
ic91 pin 7 =     0v         0v
ic91 pin 8 =    .4v      4.25v
ic91 pin 9 =    .4v        .2v
ic91 pin10 =  4.25v      4.25v

Before R61 there is 5v.

Mark