I recently acquired a IIe enhanced and when it's switched on it appears to enter the built-in diagnostics without any input from me. The usual screen images happen and the beeps at the end, however instead of a message it simply starts over. If I force it into diagnostics with the keyboard it goes through the routine and then gives me the "SYSTEM OK" message. I've removed and re-seated the ICs and thoroughly checked as well as cleaned the motherboard. It shows no corrosion or any signs of contaminants and looks very clean and undamaged.
Any suggestions as to what the cause could be would be much appreciated.