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.
