HP9100 display issue

[dbrb2]

Hi
I have an HP9100 calculator
It doesn't get turned on very much. However, when used about a year ago it was fine.
Last week I turned it on and the CRT lit - but didn't seem to be scanning properly. You could see that keystrokes were displaying, but all three lines were lit all the time, making it almost impossible to differentiate what you had typed.

Today I turned it on and the CRT didn't light up at all.

Are there any useful pointers for where I might start if I wanted to troubleshoot this? CRTs scare me a little!

Photos below:

https://photos.app.goo.gl/qaVQqvqFojPZsmmh8