What is the frame rate of your source? (some unidentified game console?)
What is the frame rate of the computer/monitor that you are trying to hack?
Many (most?) older, (and built-in, specific-purpose) CRT displays will operate only at their designed refresh rate.
Some later versions of
standalone CRT monitors were "multi-sync" and had specially designed circuits to detect the incoming rate and change the internal circuits to accommodate the refresh rate. See:
https://en.wikipedia.org/wiki/Multisync_monitor NEC had a very popular range of "MultiSync" monitors and in fact "MultiSync" is a trade-mark of NEC. Of course, since modern LCD displays have essentially internal computers to interpret the incoming signal and drive the pixels, all modern displays are "multi-sync" by definition, and nobody even thinks about it anymore, it is just assumed.
But CRT displays that are made for a specific purpose, and especially those built-in to devices (like your unidentified computer) were most likely designed to operate at one fixed refresh rate. Because it is much more expensive to make a "multi-sync" CRT display. And if you have a fixed application there is no reason to spend the extra $$$ for multi-sync.
Unless your source (game console?) runs at the same refresh rate as your CRT display, you have another dilemma on your hands. Changing the refresh rate for a fixed-rate display is for all practical purposes impossible for someone without significant experience with CRT circuitry. IF it could even be done at all (and that is a very big IF), it would take far more work than simply finding a more suitable display.
It is not just a matter of changing some components. Most CRT displays use the same "fly-back transformer" BOTH to generate the extra-high voltage that accelerates the electron beam AND to create the horizontal sweep current. Those two critical functions are inextricably combined together. It is quite a clever design to keep the cost of manufacture down to an affordable price. But because it relies on a resonant, tuned circuit, it means the the magic is "baked in" and nearly impossible to change after the fact.
When I went to YouTube and searched for "discharge CRT", it listed "About 4,510 results". The very first one "Micro Center Tech Support" seemed quite good. Remember to discharge to the spring on the outside of the tube, and not to some point in the circuit farther away. Else you run the very real risk of zaping the computer mother board.
Remember that whenever you are working with the internals of any CRT display, you should be wearing good safety googles in case of explosion. If you scratch the CRT in the wrong place, it will implode (from the vacuum), and then explode sharp shards of glass all over the place. That is why people recommend against just using a grounded screwdriver or something that can scratch the glass tube.