PDP-12 at the RICM

Jay Jaeger cube1 at charter.net
Sat Jul 11 21:32:01 CDT 2015

If you are missing other PDP-12 maindecs or docs, let me know - I may
well have them and would be happy to scan them.


On 7/11/2015 8:02 PM, Michael Thompson wrote:
>  J. Victor Nahigian donated some M221 and M222 boards for the processor and
> TC12 LINCtape controller. They are in pretty bad condition, but are
> repairable. Warren wrote a test program for the M222 boards, and some of
> the just donated boards actually work OK. It will be nice to have some
> spares.
> Dan (the donor) brought over the now lubricated top of cabinet fan. He had
> to make some special tools to disassembled it but was able to lubricate the
> dry bearings. We will reinstall it next week. He also dropped off the
> system logbook and more diagnostic manuals. More scanning for Bitsavers! It
> is really interesting to see the service history of this system since it
> was new.
> The LICM scanned some of the missing MAINDEC documentation so we were able
> to run:
> MAINDEC-12-D1AC-D Extended Memory Control (EXTMC12)
> MAINDEC-12-D8CC-D_KW12A_Clock_Test Fails test #11 where the AC should be
> 0000 and is 7777 on the CLRB instruction.
> MAINDEC-12-D8CA-D-(D) KW12 Real Time Clock Diagnostic (KW12TST) shows the
> same failure mode as D8CC.
> MAINDEC-12-D6BA VR12 Display Test Runs, but we have no display connected.
> We connected the 'scope to the outputs of the VC12 display controller when
> MAINDEC-12-D6BA was running. Without a way to interpret the intensify
> signal, and no persistence in the phosphor, the resulting image was not too
> good. At least we know that the display controller is responding to
> commands and outputs signals that look reasonable.
> We reran MAINDEC-12-D3AD-D-D Tape Control Test Part 1 of 2.
> It still fails at 3400 with the error message "LGP GP=GPC PRESET" printed.
> We reran MAINDEC-12-D3GA-D-D Tape Control Test part 2 of 2.
> That runs fine.
> I bought the matching terminator for my current probe and was able to give
> it a try today. The normal setting for PDP-12, PDP-8/I, and PDP-8/L core is
> 320mA. When we debugged the core we set the voltage regulator to the middle
> of the high and low voltage settings that caused periodic errors. The low
> going part is the read current and the high going is the rewrite current.
> The result turned out to be 316mV for the read. Not too bad!

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