Original left on glass part 2

Not long after my last post about dirt on the scanner glass causing the copier to constantly detect A3 size paper on the glass I got a call about a machine constantly detecting A4 on the glass. The machine is a Bizhub C364e that I had recently replaced a board in and the problem had occurred repeatedly since that repair. 

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.

Original left on glass

Today I went to a call for a Bizhub C754e that was constantly complaining that an original had been left on the glass and was not allowing users to copy or scan until it had been removed. However nothing was on the glass to be removed. This is not the first time I had seen this.
Switching the machine off and on again would allow users to use the copy and scan options if the document feeder was used until the document feeder (ADF) was lifted and an original placed on the glass. The problem can be replicated by simply lifting the ADF and closing it without putting an original on the glass. The detected original on the glass was always A3. The fault: dirty or streaky glass.
When the ADF is lowered it activates a switch at the back which triggers the scanners original detection. You can see this as the scanner lamp coming on when the ADF is still raised about 20 degrees. The reason the lamp comes on is because the machine is using the scanner to look for the width of an original. It is done before closing to get the contrast of the paper against the open platen cover. But this isn't the problem area.
At the other end of the scanner bed is one or more sensors that are used to detect the originals length. This is what detects the difference between A4 and A3. It consists of an infrared LED and a detector. Infrared light is shone up at the original and if an original is present will be reflected back at the detector. This can be tested in Sensor Check under State Confirmation in Service Mode.
But if there is no original what is the sensor detecting?
The first time I saw this was in an office where the copier was located near a kitchen. It seems that someone in the office took it on themselves to clean the scanner glass and used the conveniently located dishwashing soap to do it. The soap left a film on the glass that looked clean but was refelecting the infrared light back to the sensor. I gave the glass a good polish with a dry cloth and the problem went away.
However today's machine is not located near a kitchen nor had anyone owned up to cleaning it recently. But after giving it a good clean and polish the machine started working again.
Another thing to keep in mind is that we have had problems with a copier that would have this problem only late in the day. About 4pm this problem would happen but the next morning it would be fine. After arranging to have a tech arrive after 4pm it quickly became clear that the machine was near a window and the afternoon sun would shine through into the scanner. It was the sun light messing with the original length sensor and of course the next morning the sun would be shining from a different direction. That was easily fixed by closing the curtain.