I sell lots of IIe's and this only happened to one customer, I think it was caused by the aging caps in it, I was not there so I can not say for sure, another power supply should fix it or you could very easily just swap out the old caps for new ones and see if it fixes it. I have seen several types of power supplies used on the IIe's so it would be hard to find an exact schematic but it should be straight forward.