It won't be the CRT so long as you immediately turn it off and keep it off until you fix the problem. Vertical and/or horizontal collapse is a quick way to burn the screen phosphor.
If you must do debugging with the machine on, reach under the bottom left of the bezel and roll the brightness knob all the way down to where you can barely see the raster to avoid burning the screen.
There could be several things wrong with the analog board that would cause the screen to collapse, as well as on the yoke. I'd recommend starting off with reflowing ALL of the solder joints on the analog board and doing a recap on it. I'd also recommend recapping the power supply, because those are notorious for capacitor leakage.