I know, it's really important to preserve it. I have the experience to troubleshoot this kind of thing, but not without the manual. Been looking for the manual for many years. LOL before the internet. A friend, Paul Porter, has one specimen of the color version, the PJ-700? He claims to have a manual and that the -400 can be fixed with that manual, but has never been able to find it and it's been >30 years.. but he has a 10 acre "junk farm" with many buildings and stacks of stuff all over. He worked for Sony broadcast service for many years. Has lots of TV sets of all kinds, tubes, some CRTs, etc.
These may be interesting to look at - about Paul's collecting:
1.) my pictures of a little bit of the stuff at the junk farm:
http://bunkerofdoom.com/hoard1/index.html
2.) my pics and videos of the overflow stuff stashed at nearby Bomber Bait:
http://bunkerofdoom.com/hoard4/index.html
3.) Paul's youtube channel:
https://www.youtube.com/channel/UCqg...8TVWc6bscdNYiA
(not everything shown is still there - he has been been trying to 'cut back'.)