Open up the computer, take off the white shield (those black plastic push rivets come apart, and can be reused), and start soldering.
This is one of the simpler fixes, as there’s not a whole lot of taking apart, but if ya don’t have a 9” T-15 screwdriver to open the case, it’s not easy at all......
Cracked solder joints at the cable connections (Yoke/CRT and Analog to Motherboard connectors), and certain areas about the high voltage circuit like the cap and flyback transformer.
But do not just add solder or reheat the joint. You need to remove the old solder, clean up the board and circuit part with some IPA, and then solder with fresh solder off a spool.
I can also reinforce what already has been said with cold solder joints. I got a new to me SE30 this week and one pin on the P1 connector on the analog board had completely broke away from the solder.