> -----Original Message-----
> From: cctalk-bounces_at_classiccmp.org
> [mailto:cctalk-bounces_at_classiccmp.org]On Behalf Of Tony Duell
> Sent: 19 January 2004 22:01
> To: cctalk_at_classiccmp.org
> Subject: Re: 'not well' Osborne 1 mk 2
>
> Presumably this is a conductive coating on the inside for RFI reduction.
I'd assume so. Fortunately I didn't damage owt.....
> The pinout is much the same as the 2716 EPROM, but with Write Enable/ on
> pin 21. It's one of the pinouts that burnt into the permanent ROM of my
> brain :-)
Heh! I grabbed the technical manual this morning from Bob Feldman's post,
and that told me the video RAM was a 4116 that's stuck under the
double-density secondary board - the one that's supported by glued-on
mountings. Bah. The board is now resting on an old book that shouldn't be
conductive, so now I just need to find a capacitor that gives me +5V for my
probe and I can start investigating properly-ish.
> Well, in my experinece, static RAM tends to initialise to the same state
> on each power-up. And if you're getting recognisable characters, it
> implies the video timing chain, the chracter generator, etc, are all
> working correctly.
Yup.
> So either there's some problem where the CPU can't write to video memory,
> or more likely the CPU is not trying to write to video memory. Maybe a
> RAM, ROM, or bus problem?
Well, the CPU is producing activity on its address lines, but maybe it
doesn't get much further than that. As luck would have it the ROMs are
obscured too :-/ The system should run without either the floppy board or
double density board, but it seems the power for the monitor comes from the
floppy board, and the floppy board is well double-decked over the
motherboard since it utilises at least 2 of the sockets on the motherboard
to connect, one of which is the CPU!
I'll have to go for a total dismantle when I'm not painting doors or fixing
the Missus' laptop......
cheers
--
Adrian/Witchy
www.binarydinosaurs.co.uk - possibly the UK's biggest online computer museum
www.snakebiteandblack.co.uk - ex-monthly gothic shenanigans :o(
Received on Mon Jan 19 2004 - 17:20:19 GMT