I just opened this beauty for a quick inspection of the internals. You can look at the pics, not high quality, just iPhone camera under non-perfect lighting. But size wise well over the forum limit, so check the link to my GD at the end of the post.
A few observations.
First, caps look very good for the age. Not a tiniest bit of bulging nor any thermal stress signs that I could notice.
2nd, inside is very dusty. Especially top board. Which is timebase board as far as I understand. Might do some air dusting of the insides of the scope. Any advice on dusting an old scope?
3rd, I did not notice any thermal stress on any components except for the big green box named HV-cascade on Z-board at the rear and a few components around it. I don't know what it is, will read.
4th, I was a bit surprised first when I noticed that CRT tube (rear end) connections are not soldered. Wires leading to pins have kind of inserts instead. On a second thought, I remembered that I haven't seen any tube soldered actually (my father was very into restoring of old tube radios, I have his collection of 20+ mid 20th century ones and a heap of parts on my hands now and don't know what to do with it...). Quite logical not to do quick thermal things to big glass thingy empty with vacuum
I moved the inserts up/down a bit (bad contacts thinking).
That's it regarding inspection.
I put the case back on, turned it up and it seems that state of things has changed...
Problem has not disappeared, but symptoms has changed a bit. Not that it makes things more clear to me.
First signs of the problem appeared later than previously. Previously it took 10-15 minutes, now I waited for almost 30 minutes before it happened. Tapping does not help anymore, even more than gentle tapping does not. I tried messing with controls while it did the thing, not that I could notice any correlation. Problem appears for much shorter periods now, goes away quite quickly itself. After ~ one hour it seems gone. Scope is running for more than a second hour now and I have not noticed the problem since approximately during the second half an hour of operation.
I'm still thinking-hoping that it's a contacts/pots problem. How do you address a pot problem btw, replace the pot?
I took a few ~30 sec videos while the problem manifested itself. It seem that this forum does not support video attachments (and why should it?) so I uploaded to Youtube. Check the following links if you want to see and comment. I'm not a Youtuber, so let me know it links does not work.
https://youtu.be/sm4o18oqQRwhttps://youtu.be/JJOuPvmr738https://youtu.be/KoutXDdCfQkLink to pics:
https://goo.gl/photos/tArA5ZYK5fR3d52R6