Or, we could always do a tiny bit of troubleshooting to see what his problem really is...
All we have to go on is that it's dim and he hears a whining sound. Is it the flyback? Who knows? He doesn't even know what kind of monitor it is, so he hasn't looked at it yet.
The dim picture could be a weak tube, a misadjusted brightness control, or the face of the tube could just be really dirty (common on Space Invaders, since the tube faces up, with a mirror to reflect the image).
The whining noise can be any number of things - from a loose flyback core to a bad transformer, loose yoke winding, loose width coil, or the hold being slightly out of adjustment. It's also pretty normal for a flyback to make a bit of a buzz if the center core is loose, in which case you can shim it up with a toothpick. Might even be one of the flourescent light fixtures in the game, and not the monitor at all!
It's just that as soon as someone posts a problem everyone jumps all over it listing tons of parts to replace, without actually doing any diagnosis, or even knowing what the device in question is! Sure, all monitors this old probably need to be capped, since electrolytics fail with age. But you have to start with troubleshooting. Clean it up, check it out, check the voltages, see what is _actually_ wrong with it, before changing out tons of components.
-Ian