Since the beam lost vertical and horizontal travel, it suggests loss of voltage on your horizontal and vertical plates. Most likely culprit is power supply failure or rather the section of power supply which produces plate voltage. It may be a bipolar supply.
Have you opened up the housing? Does the board have labels indicating volt levels, test points, function, etc? There's a high voltage hazard of course. Example, the beam is 1,000 V or more. The plates may get 100 to 200V. Keep one hand in your pocket if you decide to poke around.
You may see burned components. Only if you're lucky are those the only components that need replacing.
Or you may spot a blown fuse for the plate section. Replacing it may restore operation. If you're lucky that's all it needs.