This is most likely because the power supply is detecting an intermittent overload and is shutting down for safety reasons, and although I am not 100% positive that your model is included I do however suspect that it is, and suffering from a very common complaint across a large range of models from that era whereby the notorious C926 capacitor goes faulty, this being associated with the vertical drive IC. This cap can also have a different number dependant on the chassis used, but its always in roughly the same location near to the v/drive chip, which by the way can on occasions sometimes suffer from dry joints on its connections on the PCB.