Have you checked all your ground reference points. GDR starts at the Miprom II power supply. I don't have a print for the drive you are working on. Page 7 on mine shows the power supply. L1A is fed in Then follow the GDR out and make sure you haven't lost a ground somewhere. If it ran for a while I would be looking for loose connections. Also GAN is another reference point, and L1A is system ground.
