SM 74 Double Sheet Detector

How can we check the double sheet detector of the SM74 ,if its working or not.
Its a year 2000 model with CPtronic compact.
Machine stops at when sheet arrives at front lays and gives double sheet error. This is happening on both pull lays.

 

Replacing the double sheet detectors on an SM74 is not so easy. Underneath the feed board on the DS you should find a black box which is mounted to the side frame. 1 screw in plug should be connected to the bottom of the box. On the top or side of the box should be 2 black wires which go to your double sheet detectors. If something is wrong with these wires or the box itself, you need to replace the whole system. Check to make sure that the screw in plug is properly connected. Its strange that both sides are not working. Go to service wrench 2 V/A screen. Scroll through the screens and there should be a screen that has EWK on top. The first two numbers are your double sheet detectors. Make sure that the side guides are down in the pulling position 50-60 degrees should be fine. Manually life the guide and see if you are getting a change on either of these 2 numbers. Switch guides and do the same. If you are maybe the sensors just need to be adjusted. If you aren't getting anything I suggest you get a tech to look at it and possibly replace the system or the cable going to the black box.

 

Thanks exheidlberg for your reply..can you tell me what is the adjustment process if sensors are working?

 

With the selected side guide down in the pulling positon the value on the V/A screen should read between 380 and 760. Adjustments can be made on the adjusting screw in front of the pull wheel. loosen the locking screw and turn the allen in or out to get proper value reading.

 

Problem solved by adjusting the control disc but two more issues.
1) When sheet size selected from CPTronic, pull lay is not moving to the selected size.
2) I adjusted the feeder timing to 300 degrees and now I get sheet advanced error, earlier the feeder timing was at 334 degrees.
Any ideas?

 

If the side guides are not moving to the correct position usually its the pot or motor for that side guide. The motor has a pot inside for rough positioning and there is an external pot for fine movement. when the side guide positions it should move toward the side frame and when it reaches its rough position it should move back toward the middle slightly for fine positioning. As for your feeder timing issues, 300 is the correct timing for sheet arriving at head stops. if you still have an issue check feeder head timing to feeder. forwarding suckers should let go of sheet when the forwarding wheels are 1mm from the forwarding shaft. Also, make sure you front allignment eyes are set correctly

 

Both side lays are not moving to selected size, We can move the side guides with coarse adjustment which is used for off center position.

 

sounds to me like the external pots

 

By external pots, you mean thr 1R11a/1R12a units installed beside the motors of sidelay.

 

yes

 

Can this be a faulty SSK board?