> > The processor and core memory in the PDP-12 are working very well now, so > we spend some time with the TC12 LINCtape controller. The TC12 is very > intelligent compared to the more modern TC01/TC02/TC08, and the lobotomized > TD8E DECtape controllers. The TC12 designers included lots of back-doors to > make diagnostics more effective. You can even emulate the data coming from > the TU56 to see if the TC12 processes it correctly. > > The MAINDEC-12-D0GA-A Tape Quickie ran OK and just tests that the TC12 > registers can be written and read back. > > The MAINDEC-12-D3AD-D-D Tape Control Test Part 1 of 2 ran for a long time > and then displayed "LGP GP=GPC PRESET". It pointed to an M216 module that > uses the SN7474 ICs that have caused lots of trouble on other modules. It > tested OK, so we put it back in. We will consider replacing it anyway if we > see further problems. > > The MAINDEC-12-D3GA-D-D Tape Control Test Part 2 of 2 ran OK as long as > you held the MARK switch on the console down. The MARK switch on the > console allows a program to turn on the MARK Track flip-flop in the TC12. > This is not documented in the manual, but was a hand written note in the > margin. > > The MAINDEC-12-D3FB-PB Tape Data Test ran for a long time writing patterns > to tape and verifying that they were written correctly. This means that > lots of the TC12 LINCtape controller is working, as well as the TU56 tape > drive. It eventually failed when it tried to verify the block numbers. We > are not sure that the scratch LINK tape that we used is good, so that may > be a contributing factor. Maybe we can get the MARK-12 program working and > we can reformat the scratch tape. We have just a few LINC tapes and need to > image all of them before we write on them. > > Two more lights on the front panel stopped working. We tested the SN7400 > ICs that send the signal from the registers to the front panel, and they > are OK. The bulbs are OK, so the transistor that turns on the bulb probably > failed. We already replaced one for the LINC light, so we know the > procedure. > > We are getting close to the point where we will need the VR14 display > working to continue our work. Getting the display working will be quite a > project. The PVA between the CRT and the shield has degraded and is nearly > opaque. We will need to remove the outer CRT glass shield and remove the > degraded PVA. Most restorers just put double-sided tape between the shield > and the CRT so that it will have the right dimensions in the clamp. We are > considering replacing the PVA to make is safer. That will be quite a > project. > > Warren modified the current-loop to RS-232 adapter that he made so it will > run at higher speeds. We needed to remove "C1" from the W076 console module > so we could run baud rates faster than 110. After testing, it looks like > 1200 baud is the best compromise between reliability and performance. Now > we can load diags 10x faster. Very nice! >
We scanned some of the PDP-12 diags, and Al put them on Bitsavers. We will scan more this week and send them to Al. -- Michael Thompson
