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!