I worked on a awg2021 and I'll bet your problem is overheating. The 2000 series uses ECL logic and those chips get extremely hot! With the cover off be sure to always place a good powerful fan pointing at the card cage on the right side of the unit. When I worked on mine I sat it on its left side and rested a 12v PC fan on top of it pointing down. Make sure that the fan in yours is working 100% and really moving air. It's loud but absolutely necessary. It should draw air in through the holes in the back-right of the cowling, through the length of the card cage to the front, across to the CRT unit and power supply on the left and out the left-rear.