Fixed my pdt11/150
cz at alembic.crystel.com
Sun Apr 26 15:33:25 CDT 2020
So I've had a boat anchor pdt11/150 here for awhile. It's probably one
of the weirdest pdp11s ever built: An 11/03 CPU ish, six serial ports,
ish, and a pair of RX01 drives.
The trick is the system is very closed in: There are 4 boards inside
with a lot of early microprocessors to do the IO instead of a real Q
bus. The bottom board is a controller that is sort of like an RX01 but
instead of using the DX: driver it uses a special PD: driver. The CPU
connects to this with a 14 pin DIP ribbon cable, and on the back of the
CPU module is a 64kb memory module and a serial module that has a
console, printer, modem and three additional serial ports that are their
Problem with this one was that it would not come up. Serial tests seemed
to fail using an error code of waiting for input which didn't make a lot
of sense. So today I decided to pull the serial board and see if I could
swap the UARTs.
I quickly figured out the problem: The serial board "connects" to the
main board by two sets of bars with three screws each that hold the
board to an interconnecting header that sends the signals. As soon as I
loosened the screws I realized that the header isn't connecting to pins
on either board, it literally presses against pads on the boards that
complete the circuit. Nothing but pressure and springiness holds it
together. No screw, pin and socket, anything.
With that I cleaned off the headers and wiped down the pads on the
boards till they shined like the top of the chrystler building. I then
reassembled and torqued the screws down evenly, finishing with the
center screw first followed by the outside screws. It is to note that
the hinges that hold the CPU and memory/serial boards to the body of
this thing attach to the bottom of those screws so when you open it up
you are flexing the assembly and probably stretching the screws a bit.
Which results in bad contact...
Plugged it in and all is well.
RT-11SJ (S) V05.01C
SPCINV.SAV 10 21-Mar-1989 OTHELO.SAV 45 21-Mar-1989
SPCINV.DAT 1 21-Mar-1989 TODAY .SAV 20 22-Feb-1988
DECMAN.SAV 14 21-Mar-1989 SPACWR.SAV 13 21-Mar-1989
STRTRK.SAV 54 21-Mar-1989 SWAP .SYS 26P 27-Jul-1984
RT11SJ.SYS 64P 19-Jun-1988 TT .SYS 2P 19-Jun-1988
PD .SYS 3P 19-Jun-1988 DX .SYS 4P 21-Jan-2000
PIP .SAV 30P 21-Jan-2000 DUP .SAV 52P 21-Jan-2000
DIR .SAV 20P 21-Jan-2000
15 Files, 358 Blocks
128 Free blocks
Another little DEC mystery solved. One odd thing about these: There are
only four chip slots for the CPU and microcode, but one of the carriers
has two dies on it so the system *does* have EIS and FIS instructions.
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