Since the last thing to happen to the copier was the board replacement I first had another look at that board to see if a connector was loose. I pulled the copier out away from the wall and took the rear covers off to have a look but found nothing wrong. I tested the copier before putting it back together and could no longer get it to detect A4 when there wasn't one on the glass. Yay, fixed. I put the covers back on and pushed it back into place and tested it again and the problem was back. Hmmmm.
As in my previous post the copier looks for an original on the glass when the ADF is lowered. With the last problem it was the original length sensor that was detecting something that wasn't there. This machine was using the scanner CCD to detect something that isn't there. Testing different combinations of A4, A4R and A3 showed me that the problem was towards the front of the scanner because it couldn't tell the difference between A4 and A4R. The copier was seeing something at the front of the glass that it was interpreting as an A4 length piece of paper.
The problem only occurs when the machine is against the wall so I pulled it out away from the wall and tried again. No problem. I have an idea. I look at the carpet for divots left by the copiers castors and found none. This is really nice carpet and the machine has not left a mark on it since it was installed. This also means that I don't know where the machine was exactly positioned when installed. Aha!
When I had the original problem I moved the machine back against the wall and a little to the right away from a shredder that was there. I thought it was a little close and there was space for it to be moved so I did. When I pushed the copier back 10cm to the left closer to the shredder the original detection problem went away. So the position of the copier was causing the problem. Why?
With the copier 10cm to the right the scanner mirrors are directly underneath a set of ceiling lights and when the ADF is lowered the scanner "sees" the light and is interpreting it as light reflected off a piece of paper. A few cm in any direction puts the mirrors out from under the light and the scanner cannot see it.
So remember: Position, Position, Position! If the scanner is detecting something that isn't there try moving the copier a little.
