Hi Bruce,
I think I found the memory problem:
On Mon, Jun 18, 2012 at 7:07 PM, Bruce <Bruce at wild-hare.com> wrote:
I'm confused. ?The VC (Virtual Console) works okay
when you hit the reset
button, but when the computer is powered on you do not get the
OK
!000000
!
indication? ?(...per Chapter 5, Computer Self-Test, page 23)
Correct. On power on I only get an "O". VC does not respond at that
point. Once I hit the reset button, I do get
O000000
!
The VC then responds as expected.
If I remove the memory board, the behavior is exactly the same, except
that every memory address reads back as 177777 of course.
Accumulators with and without memory board:
without - 177777 125252 076000 000701
with - 127252 125252 076041 000701
This lead me to suspect that the memory at word 41 was incorrect.
Memory locations 0 - 40 were 052525, 41, 45, 51 were 127252, 42 and up
(except those with the lowest bits being 01) were 125252.
So, it looks like the entire memory is written with 125252
(1010101010101010) first, then each word is first read, then written
with 052525 (0101010101010101).
Sure enough, when I wrote 125252 to word 41, it looked fine, but when
I wrote 052525 to word 1, it changed word 41 to 127252!
So, it looks like the memory chip that controls bit 10 for addresses
ending in 01 (binary) is at fault here. I'm going to do some wire
tracing to find out which chip this might be...
The part numbers (005-xxxxxx-yy) are important when
trying to determine the
exact computer configuration as the same board may have different part
numbers depending upon what chips are stuff onto the board (i.e. memory
boards). ?If no 005 part number exists anywhere on the board the board
artwork 107-xxxxxx-yy number may be used in extreme situations. ?I do not
know of a 107 to 005 cross reference table but I could look at various
in-house boards if needed.
Like I wrote, the CPU and Memory board only have part of the label
left, it looks like the actual part numbers have carefully been
clipped off. All that remains are the "E" numbers, which I presume are
a serial number. The numbers on the boards themselves read:
CPU: 10700094903/0 07 (last 07 is printed, rest of the number is copper)
Mem: 10700081303/03 (entire number copper)
Also, the S/140, Nova 4/S, Nova 4/X could interchange
boards (CPU and
memory), so this system might not be a "true" Nova 4 - Eclipse boards could
be used rather than Nova boards if a Field Engineering guy didn't have the
"correct" parts. ?Nova/Eclipse CPU boards could be interchanged if the four
(4) PROM "personality" chips were swapped.
Could that be the reason the part numbers have been removed?
Although I don't think it's likely; all the PROM chips are soldered on
(no sockets), so swapping wouldn't be all that easy. Plus, the
soldering on the PROM chips looks like it's untouched.
There are a few other areas of the main board that do show evidence of
repairs; the following parts seem to have been replaced at some point
(with approx. board locations):
- One of the IDM2901A bit slices has been replaced with an AM2901BDC @ AE11
- 74S241 @ X13
- 74LS38 @ E45
- 4 75451 drivers around E22
Thanks,
Camiel.