PDP-12 Restoration at the RICM

Robert Jarratt robert.jarratt at ntlworld.com
Mon Jun 1 03:33:26 CDT 2015

Yes, the new rubber hammers are available from David Tumey. I think he wants
about $7 for 10 of them. I have a supply of them here in the UK for anyone
that needs any.



> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Cory
> Heisterkamp
> Sent: 31 May 2015 15:48
> To: General Discussion: On-Topic Posts
> Subject: Re: PDP-12 Restoration at the RICM
> Michael,
> Sounds like you're making some real progress. Next time you're near the
> ASR33, check the rubber hammer for the print cylinder. These have a
> to self destruct and in doing so, destroy the cylinder itself...and they
can go at
> anytime. There's a fellow on the Greenkeys that has tooled up and is
> replacements; same profile as the original and easy to install. Cheap
> really. -C
> On May 31, 2015, at 8:08 AM, Michael Thompson wrote:
> > We spent some time on the console Teletype that came with the PDP-12.
> > The platen was nearly impossible to move, so the Line Feed did not
> > work. We removed the platen, and found that the plastic in the bearing
> > area had swollen and was binding. We sanded, cleaned, and lubricate
> > the bearing surface and the platen now turns freely. On reassembly we
> > found that none of the Control Characters like Line Feed or Bell would
> > work in Local Mode. We fiddled for quite a while, but did not find a
> > problem. We speculated that something got bent when it could not move
> binding platen.
> >
> > We found a bad SN7474 E13 on the M706 Teletype Receiver flip-chip from
> > the PDP-12. We will repair and test it next week.
> >
> > We borrowed the M706 Teletype receiver from the PDP-8/I and connected
> > the Teletype to the PDP-12. We loaded and ran a toggle-in program that
> > echos the keyboard to the printer. We were a little surprised when
> > everything in the Teletype worked OK. We were even more surprised when
> > the Teletype now worked correctly in local mode.
> >
> > We borrowed the console cable from the PDP-8/I and connected my laptop
> > to the PDP-12. The terminal emulator worked correctly and echoed
> > characters to the PDP-12 and back.
> >
> > We toggled in the RIM loader and then loaded the LBAA BIN loader from
> > my laptop. We ran the BIN loader and loaded and ran the PDP-8/I
> > Instruction Test #1. It actually works OK!
> >
> > We tried twice to load MAINDEC-8I-D02B-D Instruction Test #2, but
> > failed both times. Running that diagnostic and others will be the
> > project for next week.
> >
> > Al Kossow posted LOTS of PDP-12 manuals to Bitsavers. One manual
> > includes the allowable ripple for the power supplies. They allow
> > 3,000mV of ripple on the -30V supply for the core memory, so I guess
> > that the 180mV that we measured two weeks ago is OK.
> >
> > On Mon, May 25, 2015 at 8:07 PM, Michael Thompson <
> > michael.99.thompson at gmail.com> wrote:
> >
> >> Today we pulled all of the M113 flip-chips and tested them because
> >> SN7474 and SN7400 ICs seem to be a problem in these early DEC
> >> systems. The ones in slots J33 and K30 were bad. Replacing them fixed
> >> the problem with the JMP instruction. We did some more testing with
> >> the toggle-in programs and found that ISZ cleared the AC. Replacing
> >> the M119 in slot H28 fixed that. All of the toggle-in tests pass, so
> processor is substantially functional.
> >>
> >> Core memory in field 1 with addresses X5XX didn't work. We replaced
> >> the
> >> G221 in slot D10 to fix that.
> >>
> >> We tried the ASR33 Teletype that came with the system. The mechanics
> >> were sticky from not being used for 30 years, but we got most of it
> >> free and working. We could send characters to the Teletype, but could
> >> not receive anything. The M706 receiver failed in the board tester.
> >> The spare is also broken, so we need to fix both.
> >>
> >
> >
> >
> > --
> > Michael Thompson

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