Date : Sun, 08 Feb 2004 23:52:38 +0000
From : Richard Kilpatrick <oldcomputers@...>
Subject: Re: Tube ULAs
> Duh - actually yes you did already send one, I just found it :-)
As always, share and share alike :) I don't like to get stuff like this
without at least providing pictorial evidence of it's existence.
> Do me a favour and double-check the 286 CPU is in the socket properly
> will you? :) (I have a nasty feeling that chips can be put in those
> sockets in any orientation by the way - be careful)
They could in theory - they have notches which makes it tricky to do
so, and it was playing up before I examined it :) As it is, I didn't
move it.
> I notice from the photo the jumper's set to 1MB memory at the moment -
> just a thought but put it to 256KB as a test. Hopefully if there *is* a
> memory fault you'll get lucky and it'll be in the 768KB you switch
> off...
I'm not sure how that works, but I'll try it. Personally I think that
the EPROM is failing to initialise to that stage.
> What's the empty DIL socket for next to the ULA? Any ideas? (just
> curious)
I'd wondered about that - as you'll know the 32016 also has one. I
think that it was either to install a math processor, or possibly a
test probe socket.
> you tried the known-good B+ board from the ACW though didn't you?
> Hooked
> up to the 286 copro board and the ROMs from the ABC swapped in?
Well, I could put the BOS ROM in the ACW and try that, but I'm
confident that the 4.87V is sufficient to run the 286.
> OK so B+ board fault is ruled out, at least as far as te copro's
> concerned; make sure you rule out cable and PSU too. Double-check CPU
> socket. Other chips have been reseated...
*nods* I will try the PSU from my Z80 copro. It will probably be
reliable.
> OK, possible memory fault. Possible ULA fault (yuck). Possible ROM
> fault
> (also yuck). CPU clock problem (do you have a 'scope to check that?) or
> CPU fault itself.
ULA - we can probably discount that as swapping the ULA between it and
the Z80 made no difference either way - Z80 works fine, 286, cursor.
> When you get access to an eprom reader you'll be able to see if you can
> at least get data from the roms. (thought - you didn't accidentally put
> the roms back in the wrong order did you? The one with the orange
> sticker was nearest the ULA in the photo you sent me the other day)
I haven't removed the EPROMs, merely lifted them slightly then reseated
them. The 286 board is quite flexible so I don't want to put too much
pressure on it.
> Oh, what's the 2-pin header for by the ribbon connector? Looks to read
> "IR SW1"?
I'm guessing it was intended for if the card was used outside of an
ABC, but I'm not sure. I cleaned some dirt/corrosion from nearby with
no effect.
If anyone has a B+ board spare, I'm up for having a go at adding the
video header - it's only five or six pins. The other connectors won't
be significantly more fiddly just as normal!
Richard
--
Richard Kilpatrick
Older than most of his computers, but not by enough to know better.
Acorn: '82 to '98. Atari: '79-84. Apple: '84-04 (no Apple //, for
shame!).
http://www.dmc12.demon.co.uk/retrotech/