Does the focus control do anything?.
Looks pretty simple to fix, with VERY few options.
Most likely (historically - not just on scopes) are the high value resistors either end of the focus pot, including the series row of them. Commonly high value resitors go high or O/C, particularly ones put in series like these. Next likely option (but a lot less likely) is the decoupling capacitor on the output of the pot, that could have gone short.
As you have an EHT probe, it should be simple to find out what the problem is.