Excessive vibration on a screen 4100

[ctptech]

Can Anyone help me please. I have a screen 4100 that vibrates when the drum spins up .it sounds horrible and affects the image . It’s better when drum speed is reduced but still there . The belt has been changed as the balance blocks and clamps . It rotates smoothly by hand . No errors . Everyone is baffled . I did notice some yellow weights stuck in the side near the balancer weights . Does anybody know if they’re meant to be there ? TIA

 

[maxon]

The glued blocks are set in factory for dynamic balance do not mess with them. Ask a qualified tech to capture live serial data from the machine (diag) while running the balancer test he should understand what's going on, it seems the balancer weights slip away from position while drum is spinning up.
Clean the drum grooves and all half circle segments. Turn off the machine, rotate the drum and gently push in each balance block one at a time - this should "free" the block and allow it to roll inside the groove, then retract your finger and the block should stay put with rubber pins firmly against the metal half circles. Do this for all 4 blocks. If a block doesn't "grip" correctly it will definitely slip away during spinning. The machine may put up a mechanical error or not depending on how much the block moved from position, also depending on machine firmware. Later FW versions have much better balance calculation.
Were the values entered correctly for clamp and balancer weights ?
Were the half circle segments fitted correctly ?
Clean the bal blocks sensors on each side and make sure each block metal flag is at correct distance from the side sensor.

 

[ctptech]

Hi .ive checked the blocks and they’re fine in balance test .the numbers are ok .i had a 4300 last month where the blocks were slipping and had to replaced 2 retaining rings . This cured the errors but this fault is different . I’m worried that it’s the drum bearings . They’re not in the parts book and the other screen techs I’ve spoken to have never changed them . I only normally work on 4300 so I’ve never seen the yellow blocks . I don’t think it’s a block clamp issue as increasing and decreasing clamp weights and blocks weights makes no difference to the vibration. There’s literally nothing else other than the encoder , motor and drum vac sensor .

 

[maxon]

I put my money on the servo pack. Hook a dual channel scope on the motor connector, the waveform and phase may tell if it's an inverter problem or mechanical.
You replaced the belt, did you check the AC Servo pack offset and gain ?