Commodore PET 2001 with screen problem

One other project I'm having some difficulties with is a Commodore PET 2001 that I've had for 10 years. In that time, turning it on only ever produced a 'blank' raster screen, as in this video: https://www.youtube.com/watch?v=m5Rkwu858zA For years I assumed the computer was basically dead and kept it on static display. But just recently I acquired a good working 2001-16, and discovered that I could use its monitor with the 2001-8. I discovered the standard garbage screen, and after acquiring a whole bunch of rare NOS 6540s, and some 6550 RAMs, was able to get the 2001-8's motherboard fully functional. The screen however remains the same. I have connected it to the other working PET to no avail. I have even used the working PET's own cabling. So my problem is basically the video board. I've fixed the brightness control but that's as far as I've dared go given the voltages involved with a CRT. Wondering if anyone has any other ideas on where my problem could be. Thanks!! Brad