-----Original Message-----
 From: cctalk [mailto:cctalk-bounces at 
classiccmp.org] On Behalf Of Diane 
Bruce
  Sent: 19 January 2015 21:29
 To: General Discussion: On-Topic and Off-Topic Posts
 Subject: Re: VT101 8085 CPU Fault
 On Mon, Jan 19, 2015 at 08:48:04PM -0000, Robert Jarratt wrote:
 > -----Original Message-----
 > From: cctalk [mailto:cctalk-bounces at 
classiccmp.org] On Behalf Of
 > sandy hamlet
 > Sent: 19 January 2015 19:38
 > To: General Discussion: On-Topic and Off-Topic Posts
 > Subject: Re: VT101 8085 CPU Fault
 > 
 ...
 > > might have two devices trying to access the same line at the same 
time.
   > Devices
on the same line may include a ram, rom, I/O ports, etc.
 > This could cause the processor to "hang up" and act erratic.
 > A schematic of the board would be helpfull if you have one. 
 Something like
 
https://archive.org/details/bitsavers_decterminachematicFeb82_6949589 ? 
 
Unfortunately not. I already have that print set, but it is for the VT100,
this is a VT101 and the terminal controller board is different. Looking more
closely at the VT100 basic video board, some of the ROM part numbers are
similar to the ROM I have, but not the same. On the VT100 they seem to be
8316s which are mask programmable. I don't know if that applies to the ones
used in the VT101. If they are mask programmed then there won't be much I
can do if the ROM is bad, unless it is possible to find pin-compatible
programmable parts and a ROM image from somewhere.
Regards
Rob