Date   : Sun, 08 Feb 2004 23:15:54 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: Tube ULAs

On Sun, 2004-02-08 at 21:03, Richard Kilpatrick wrote:
> On 8 Feb 2004, at 20:35, Jules Richardson wrote:
> > Any chance of the photo of the board? Never seen a 286 one.
> 
> I could have sworn I sent you one with the Mouse board (it's definitely 
> a mouse board, the two main chips are THCT (I think) counters.). I'll 
> send another. Actually, it's online at my retrotech page in a slightly 
> smaller form.

Duh - actually yes you did already send one, I just found it :-)
So that's actually: "Never seen a 286 one - apart from the photo you
sent the other day"...

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)

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...

What's the empty DIL socket for next to the ULA? Any ideas? (just
curious)

> Done, done, done (4.87V).

that should be ok I would have thought. You tried the copro with the B+
board + PSU from the ACW right? So you've tried it with a different PSU
anyway...

> I can only assume the I/O 
> board has a fault of some sort, I've checked all the power connections 
> etc. Can't see SRAM either.

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? 

I suppose the other test is to use the known-good cable from the ACW
just in case the one in the ABC is intermittant.

I think you should have enough known-good bits in the ACW to isolate
whether the copro board is faulty or whether the problem is definitely
on the B+ side of things.

> Regardless of these problems (I wondered if the apparent lack of ROM 
> visibility would prevent the Tube code being read), it's not working 
> connected to a BBC B+ 128K either, which I /know/ has all the required 
> ROMs.

forget last statement then :)

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...

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.

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)
 
Oh, what's the 2-pin header for by the ribbon connector? Looks to read
"IR SW1"?

cheers

Jules