On Dec 13, 11:20, Joe wrote:
> At 10:06 AM 12/13/02 GMT, Pete wrote:
> >
> >How many (EP)ROMs are in it? Do they have any numbers on them?
>
> There are five sockets in a row (IC71 - IC75) but IC 75 is empty. IC
71 is an EPROM but the label in missing. IC 72 is a Hitachci PROM marked
HN613128PD11 View2-1 Japan (c)ACORNSOFT, IC 73 is an EPROM and is marked
DNFS 201666, IC 74 is an EPROM and is marked US BASIC 201667. Behind that
row is IC 52, it's marked VI (I THINK, it's stylized and hard to read),
then 403 V 2006 VC 2023 201647 (c)ACORN COMPUTER KOREA-AE. I think that's
all of the custom ICs.
Interesting. The IC numbering scheme is different. I know Acorn slightly
modified the video circuit for the US, so I suppose they renumbered IC
positions at the same time.
The first one (missing a label) should be the MOS. It makes sense that it
would be an EPROM, because Acorn regularly used EPROMs rather than mask
ROMs for "low" volume runs, which I'd expect the US MOS to be. I
discovered that pages 478-479 of the Advanced User Guide list the
differences between US and UK MOS versions. Basically, the US screen
resolutions are the same width but less high (corresponding to 1280 x 800
points instead of 1280 x 1024 -- points are not pixels though, the
correspondence depends on the screen mode, which determines the resolution
used). This is because the frame rate is 60Hz instead of 50Hz, and also
means that the screen memory usage is correspondingly lower in some modes.
The next four ROMs are "sideways ROMs" which share the same address space,
being switched in and out by the MOS. They will be prioritised from left
to right, right being highest priority. When the machine starts up, it
checks each socket looking for language, filing system, and service ROMs.
Simplifying a little, it gives each a chance to initialise, and then
allows the highest priority filing system and highest priority language to
start fully.
VIEW is a word processor, which in Acorn terms is a "language" ROM. The
version you have is the standard version 2. DNFS is a combinatin of Disc
Filing System (for 8271 floppy controller), Network Filing System (for
Econet[1]), and Tube utilites (for a Second Processor). Part number 201666
is the standard DNFS, same as the UK. The sign-on message should be "Acorn
DFS" (unless you have the Econet network interface fitted and either have
changed a link to make NFS take priority or have removed the 8271).
[1] I read somewhere that US machines were fitted with Econet as standard.
If yours has the interface, there will be a 68B54 ADLC chip in the North
West quadrant of the board, a 180-degree 5-pin DIN socket on the back, and
few or no empty positions for components around the ADLC position. And if
you hold down the "N" key while starting it up, it should say "Econet
Station 001 No Clock" instead of "Acorn DFS". The station number would be
different if someone has changed the links in the block of 8 near the
Econet socket.
Incidentally, holding down various keys can force filing system selection
regardless of ROM priority and link settings, providing the relevant
hardware and firmware is present. "D" for DFS, "N" for NFS (Econet),
<space> or <DELETE> for tape, "R" for RFS, "A" for ADFS ("F" for fast-start
ADFS), etc.
"US BASIC" is fairly self-explanatory. Like Tony, I'd be very surprised if
it were supposed to say "BASIC OS" because BASIC is not an OS and Acorn
were quite particular about terminology in many ways (they even used to get
upset if people wrote "Disk" instead of "Disc"). As far as Acorn were
concerned, BASIC (even BBC BASIC) is "just another language".
The two other similar ICs are the serial processor (near the back) and
video processor (near the ROMs). The stylised VI is the VTi logo.
> >> Actually I didn't get a cursor. I wasn't sure if it was supposed to
> >have one or not.
> >
> >Yes, you should.
>
> Hmm. Sounds like it's not finishing the boot sequence.
I think it's getting something wrong, given all those "OS" appended to
startup messages. I'd suggest *carefully* lifting all the socketed ICs and
re-seating them. I'd also suggest you temporarily remove the VIEW ROM and
see if there's any difference. Once you have a working PSU, of course.
BTW, if you're repairing that PSU, it's a switchmode. Beware of high
voltages on the capacitors (including their cases) and on the heatsink for
the power transistor. However, the standard Beeb supply (an Astec unit) is
safe to run with no load (unlike some SMPSUs), and it will shut down safely
(making a characteristic tick-tick-tick noise) if the +5V output is
shorted, and will immediately start up again if the short is removed.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Fri Dec 13 2002 - 15:33:32 GMT