VT101 8085 CPU Fault

Mike Stein mhs.stein at gmail.com
Mon Jan 19 23:15:46 CST 2015

ROM replacement is a common issue in the vintage home computer area and 
there are various pin-out adapters available for the more common ROMs (once 
you figure out what type you have); for example, maybe one of these will 
work for you:

----- Original Message ----- 
From: "Robert Jarratt" <robert.jarratt at ntlworld.com>
To: "'General Discussion: On-Topic and Off-Topic Posts'" 
<cctalk at classiccmp.org>
Sent: Tuesday, January 20, 2015 12:06 AM
Subject: RE: VT101 8085 CPU Fault

>> -----Original Message-----
>> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Matt
> Burke
>> Sent: 19 January 2015 23:23
>> To: cctalk at classiccmp.org
>> Subject: Re: VT101 8085 CPU Fault
>> On 19/01/2015 21:45, Diane Bruce wrote:
>> > I'd suspect RAM since the ROM is (I assume) masked ROM.
>> The masked ROM could be faulty. My VT100 character generator ROM failed
>> with one of the data lines floating because (I think) one of the internal
> wires
>> had became detached from the die. I replaced it with an EPROM but had to
> add
>> a few jumper wires to the legs of the chip to get the select lines in the
> right
>> combination.
> I like the idea of swapping the ROM for an EPROM (whether to write my own
> test code, or just to replace with a fresh ROM image - assuming I can find
> one). I'll probe the ROM pins at the weekend to see if it appears to be 
> OK.
> Do you recall what EPROM you used and how its pinout differed from the ROM
> you were replacing? As far as I can tell there is only one ROM on the 
> board,
> could it be both the character ROM and the firmware?
> Regards
> Rob

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