Sounds like a bad rectifier? Just a guess, I've never had much luck fixing monitors, I generally just pull them apart for components. The reason you see dimming and flickering could also be the cathode heavy metal oxide coating wearing out, or inter-electrode arcing inside the electron gun. If you open it up, don't get too close to any circuitry going to the CRT neck or flyback transformer, there are very high voltages floating around in there. Look for 3 or 4 small glass bulbs with two wires on the circuit board at the CRT neck, if they glow purple or white intermittently during operation then the voltage is going out of range (could be focus, screen, or grid voltage, I'm not sure which one.) In this case you may want to sell the monitor to a repair shop for spare parts.