Need some help getting DECmate and VT101 working

[pkhoury]

I have a total of four terminals. A parts VT101 I bought for 50 bucks, a DECmate (don't remember what I paid - maybe $200 with a keyboard missing a bunch of keycaps), and two other VT101's that I know worked. I fully recapped one of my VT101s and it's a success. CRT has minimal burn-in, connects to a PiDP-11 and all functions work.

I'm not so lucky on these two (and haven't done anything to the fourth terminal yet). I recapped the PSU, changed some diodes on the PSU that had burn marks on the PCB, recapped the analog CRT board (including changing two diodes on the terminals in this post, two resistors, the HF 10uf cap (used a poly film that's rated for HV and I know it's a good fit, as my first recapped terminal works beautifully).

I was advised to check +12. I'm sure +5 works, because I'm able to hear keyclicks and get a beep upon startup on the VT101. The VT278 shows the CPU and power okay on the back, according to the LED, and the keyboard says online, but that's it. Neither one has a glow on the electron gun. I checked all my caps on the analog boards and the polarity is all correct. I'm not sure what else to check, or where I would check high voltage to see if the tube is getting any.

And yes, before working on these, I used a screwdriver and shorted the tune's anode to ground (neither terminal had been powered up in years, but better safe than sorry).

 

[pkhoury]

For an update, I did find the pocket service guide. Checked voltages going to the controller board. I didn't record the video, vertical and horizontal voltages, but I'm getting +5, +12, -12 and -23.

 

[pkhoury]

More updates, in reference to the VT101:
Getting +12 to the video controller board. I'm not sure what +12 RTN is on the schematic, but the multimeter shows a negative voltage briefly, but nothing more than a tenth of a volt.
-23 on the PSU is really -24.40.
The interface to the flyback transformer is providing 11.68V. I'm trying to figure out the pinout to the end of the CRT tube, since it doesn't attempt to light up.

Again, both this and the VT278 never got video before recapping, so I have no clue if there are any absolute pre-existing conditions.

 

[pkhoury]

Yet another update. Reseated things, and oddly, the terminal now comes up, but I have a new issue. The picture gets shaky at random times horizontally. I've got it finally stable after playing with the rearmost POT and have brightness set where I want it. I'm very much a n00b when it comes to CRTs, learning as I go along.