1 Nov
2005
1 Nov
'05
4:14 p.m.
Hi all,
I finally got juice on the main power line connection in my museum.
I am connecting my machines bit by bit, after 2 years of inactivity.
I have found the following problem with my 11/34C.
(I will keep the description short, and tell only the end result)
The console of the 11/34C (11/34A plus cache option) shows weird
(=wrong) behaviour. It was working fine!
The display shows "000000", and the RUN LED is off.
If I press the 'LSR' button, the 'SR DISP' LED goes on. However,
if I press any of the numerical buttons, '1-6', a digit in the
display only flashes very brief. I cannot say what the digit was.
It looks like the M7859 has developed a problem.
To make things more weird the following happens if I start with
pressing the 'CLR' button and then the numerical buttons.
1) press CLR (display stays at "000000")
2) press e.g. 6 (some of the rightmost digit segments briefly flash)
3) press 6 again (1st and 2nd of the right display flashes)
4) press 6 again (1st, 2nd and 3rd of the right display flashes)
This suggests it is correctly counting the digits you enter (or shifting
them into a register), but is not displaying them correctly. And it is
only updating the bottom 8 bits.
As you probably know, the console is controlled by an 8008
microprocessor. Of course it's an 8 bit device. Maybe some 'carry' is not
working correctly.
Alas DEC didn't publish a source listing (or even a binary dump) of the
console firmware in the printset. This is going to make troubleshooting a
little harder, since you probably don't know what it should be doing. It
is clearly running a program, and that program is reading the keyboard
and scanning the display. So it is somewhat correct.
The first leftmost three displays remain "000" and do not show any
sign of changes.
Pressing 6 after the first 3 times, repeats the flashing of some
segments in the three rightmost displays.
What does it do if you press 4 repeatedly? Does it flash the bottom 3 or
bottom 2 digits? If it's only updating the bottom 8 bits, you see, then
only 2 digits will flash from 0.
So, I have the impression it has the problem to do with the M7958.
AFAIK, the entry of the digits, for example the numeric entry '165020'
does *not* need the UNIBUS, but only sets up an internal register.
The 'LAD' button, and 'DIS AD' will start a UNIBUS cycle (to access a
memory location). Correct?
I think so.
BTW, the voltage on the CPU backplane (DD11-PK) is 5.08 V. and the
+15 and -15 read +/-15.x V. (Can't remember the exact value).
I have an other 11/34 with an M7958, but never powered up that box.
I took that M7859 and installed it in the 11/34C. The display stays
dark. According to the M7859 doc, that basically means that the board
is dead. So much for board swapping. Sorry, could not resist to try
an easy success. I don't have other spare M7859 ...
You may find the totally dead board easier to debug. At least you can
check for a clock at the 8008, and for activity on the internal bus to
the firmware ROM, etc.
-tony