I have had an interesting problem with a IIe. When I turn on the IIe I get continual CRs (carrage returns) until the buffer gets full then it beeps several times and then continues to start the CRs all over again. I thought for sure I had a stuck key. I checked the keyboard switches and all the keyboard circuit but found nothing. I switched out the keyboard for one from a working IIe and had the same CR problem. So, keyboard was not the problem, must be the motherboard. Since I had a working IIe I started swaping out chips in the KB circuit with no improvement. The CRs kept coming. About the only thing I had not changed was the P/S. The computer boots and makes the proper beep but gets these CRs but what the heck, Ill change it just in case, so that is what I did. The problem went away. Wow, had not expected that. I had swapped the Apple P/W with a small ATX supply that had all 4 voltages. It was a small ATX supply that had all 4 voltages. It was a SDGR-Flex-200 that I bought off ebay and grafted on the Apple connector and added a switch since the ATX supply grounds the green wire to get the supply to turn on so it has no power switch. I connected the Flex supply back in the problem IIe and the CRs were there again. I looked at all the voltages with a scope and found lots of noise on all the voltages. This was a preowned unit so maybe I found out why it was being sold. SDGR-Flex P/Ss are small enough to fit beside the M/B in the case and comes in wattages from 180 to 300. At that time I found another Flex supply that was new and purchased it for future P/S swaps. I connected this other Flex up and did not find any of the noise as the one I had installed. I have not made the necessary connections to make this second Flex plug onto the Apple yet. I would have thought that the P/W was the last thing that could cause this problem, and it was.
This was before I saw ReactiveMicro's Universal P/S.
I sure wasted a lot of time on this one.