Problem with printing double side (Light Barrier Error)

We have an issue printing double sided on QMDI Pro.
Error = Light Barrier Covered
But we are able to print single sided virgin white sheets fine.

We have cleaned all the sensors (side lay + feed table) & disabled/adjusted the echo sensor but with no result. Also changed side lay (left to right), but no result.

Suspect problem with the 2 light sensors at the end of the feed table, but there are no cracks on the glass. Sometimes the machine will feed correctly, but will then not go onto impression. Checked pressure and pistons and all is fine (no leaks or error code). Also checked/reseated X7 plug and seems OK.

Very strange, as printing single side is 100% fine.


Thank you....NICK

 

If you have a dark area in the first 10mm to 25mm at the lead of the sheet your double sheet detector thinks there is a double. Turn off your double sheet detector and the S18 delivery sheet sensor. It also sees the dark area and thinks you dropped a sheet.

This should allow you to run.

 

Hi Paul

We have replaced both electronic eye adjustment sensors (Part# C-35), as we could see one had a loose eye. And turned off the double sheet detector (Part# 11B91).
Machine ran for a morning and now back to Error - "light barrier covered"

Which is the S18 delivery sheet sensor?
Is this the 2 light sensors after the double sheet detector near the grippers?

How do we switch off the S18 sensor?

Thanx...

 

The delivery sensor is the one behind the basket under the impression cylinder. It may be covered with powder.

Special Function 18 is how you turn of the drop sheet sensor.

 

The drop sheet sensor has been cleaned, checked and tested.
No problems there.

When the machine feeds, the paper sheets are stopping as they pass the 2 light sensor (electronic eye adjustment sensors [Part# C-35] ).
We have unplugged the 2 light sensors and the machine passes paper correctly, but will not go onto impression due to the disconnected light sensors.

Is there anyway to test the light sensors via diagnostics, to make sure that the 2 light sensors we replaced with new ones are functioning correctly?

 

There is no way to test them I am aware of. They either work or they don't. I do know they have to be aligned over each other correctly. If the upper guide plate the top eye clips to is not installed properly or the spring clip that holds the eye down is bent an not holding the eye firmly down on the guide plate the press will not run properly. Also make sure the slot the eye sits in on the upper guide is free of debris. Sometimes powder and paper dust builds up in the slot causing the eye not to mount flush.