VT101 8085 CPU Fault

Robert Jarratt robert.jarratt at ntlworld.com
Mon Jan 19 09:18:19 CST 2015

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Diane Bruce
> Sent: 19 January 2015 14:17
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Re: VT101 8085 CPU Fault
> On Mon, Jan 19, 2015 at 02:07:08PM +0100, Johnny Billquist wrote:
> > On 2015-01-19 09:04, tony duell wrote:
> > >>
> > >> I just found something interesting, the pin activity on the address
> > >> lines, RD, WR, ALE etc appears normal for a bit, and only after a few
> seconds does it all become inactive.
> http://tkc8800.com/images/vt100/VT100_Technical_Manual.pdf
> Look in section 4.2.8
> The POWER-Up adn Self-Test section.
> I linked this pdf before ;)

Sorry, I know, but the terminal controller board appears to be significantly different to the VT100, the VT100 does not use the 8085. I will have a read of the sections you indicate though.

> "Assuming there are no hard logic failures present on the board, "
> And yes the 8085 has a HLT instruction.
> Are the keyboard lights lighting up at all?

Some do, but not all, and I don't hear the beep from the keyboard. HLT is looking likely.

> If it *is* the ROM which is unlikely if it is a masked ROM, it might simply be
> lose in the socket you mentioned. It may be sufficient to wiggle the ROM
> slightly to break any oxide on the pins. Some sockets are notorious for allowing
> the chip to wiggle up due to heat and cooling down.
> Your ROM may simply be lose.

I will reseat the only socketed chip on the board to make sure. Thanks for the suggestion.



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