29 Sep
2014
29 Sep
'14
2:25 a.m.
On 2014-Sep-28, at 11:10 PM, Josh Dersch wrote:
On 9/27/2014 9:59 PM, Josh Dersch wrote:
Unless I've missed something in the way this board is organized, I wouldn't expect
to see additional X/Y addressing diodes/selectors for the parity bits. The parity bits
would typically just be two extra bit-arrays woven into the existing X/Y address wires.
If you envision the cores as being in a 3-D coordinate system, where X/Y constitute the
address space and Z is the bits in a word, the board is X*Y*Z = 128*64*18.
The two parity bits added two XY planes (planes perpendicular to the Z axis), while the
bad X address line takes out one of the 128 YZ planes (planes perpendicular to the X
axis). While you have 2*64*128 'extra' cores, and only 18*64 inaccessible cores,
the extra (parity) cores are not configured/wired in a useful way for the fault.
In principle you could hack the board to swap the bad address line with the 'last'
address line, so you were just missing 64 words at the end of the 8K but the board traces
probably aren't very amenable to such rework.
Something that might be a simple hack would be to swap two entire columns in the
X-coordinate sub-matrix, to wit: swap FD1/XS05 with FK1/XS15.
It should just be swapping two traces near the connector which goes to the addressing
board.
That should move the 64-word 'hole' from 012000 up to 036000, so the board would
provide a contiguous 15KBytes/7.5KW from 0, rather than just 5KBytes/2.5KW.
As others have suggested, I'd at least try to spot the location of the (presumed)
break in the bad address wire to assess it for potential repair first.
On 9/27/2014 2:11 PM, Tony Duell wrote:
OK -- I spent a bit of time looking at the schematics for the H215 in pursuit of my crazy
plan and I was initially puzzled -- it didn't actually look like there's hardware
on the board (or the associated control/driver logic) to actually address 18 bits. I saw
the sense/inhibit lines for bit P0 and P1 outlined, but there are no associated diodes on
the X/Y switches.
After reading through a few different sets of documentation, it turns out that these
lines are driven by an optional parity controller, the M7259 (which, when combined with an
H215, G109 and G231 makes an MM11-LP). The M7259 apparently contains the diodes
"missing" from the H215 to drive the parity lines. Of course I don't have
this board in my 11/05, which makes me wonder why it has an 18-bit core plane to begin
with...
At any rate -- I can't find a schematic for the M7259, which would help narrow down
which edge connector pins on the H215 are used for the X/Y selectors for the additional
parity bits. I could do this by process of elimination, but just in case someone happens
to have this scanned, I figured I'd ask?
Incidneatlly, no matter what it says on the cover over the core mat, you
can take it off quite easily without damage. Just don't drop it on the
corse.
If it is the core address wire in the mat, you may have big problems.
Some of these mats had the cores cast onto the array of wires, no
pre-made cores that were threaded with the wires. In which case,
replacing the wire might be impossible.
My first throught was 'have a go anyway. If you wreck the board, well, it
doesn't work now'. And then I thoguth that no, you should treat it with
care. Even if you don't have the skill to fix it now, you might do so i
nthe future. Or somebody else might have a go. In any case, you don't
want ot make thigns worse.
I do have a semi-crazy idea: The H214 I have is 8Kx18 bits (i.e. parity). If I were to
disable parity on the control boards and reroute one of the parity-related lines for this
damaged section, maybe I could get a complete 8Kx16?
I'll have to do a bit more research...
- Josh