Fixed my pdt11/150

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. Ish. 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 own thing. 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 .DIR SY: 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. Why not... Chris