CTP laser problem

[maqlatura]

Hi everyone!

I have a problem with SCREEN 8300s CTP. After exposing and developing on plates there are some strange patterns. That patterns appear only on magenta and yellow plates. I attached pictures of patterns.
At first I thought that something happened during RIP, but in RIP viewer I don't see anything.
I have two CTPs and I use Trueflow on both. On one there is this pattern and on the other there isn't. So it is a problem with CTP.
I use termal positive plates, laser power 2400dpi on 70%, 600rpm.

 

[Gianni_S]

Hi, have you cleaned the laser?
Could be a diode that doesn't image perfectly at that screen angle.

 

[yavo]

Hi
You can change the angle of magenta and black colors.
However dot type use round dot helpful you.

 

[aligh]

hi
please check vacuum unit (show 600 in expose time) and clean vacuum hole on drum 's surface .
check angle of magenta and yellow in your rip.and another setting(dpi.dotahaoe.resolution)
before this problem does plate setter work with this setting (70% and 600 rpm)?
did you change your plate?(example change positive fuji plate with positive tiger plate)
regards

 

[maqlatura]

I cann't change angle of magenta and yellow - if I do that I will also change angle of cyan and black. Cyan and black plates doesn't have these patterns. I tried to clean laser haed and it changed nothing. I also try to change manufacturer of plates - still patterns are there on magenta and yellow. And plate setter worked with the same settings before this problem appeared. Also I thought that sensor surface is scratched during cleaning, but it is not. If sensor surface was scratched patterns would be on all four plates.

 

[Johu]

Does it happen on all line widths?
Have you tried different SPM?