PDP-12 Restoration at the RICM

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 the 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: -- Michael Thompson