Help with lines showing only on black

[vance]

I recently had a technician change some diodes on a heidelberg topsetter. Now I am getting these lines on the black plate.

I cant be sure that we didnt change anything on the RIP these past months as we have been troubleshooting other problems... but we havent had these lines before.

The technician is saying that these lines can only be my RIP.

Anybody has an idea what the problem is?

 

[Magnus59]

They look like the lines you get when either your lasers need calibrating or your lead screw needs lubricating, however it should be on all colours. It may be that the combination of calibration error and screen angle may be causing the lines to be more visible on the black.
I would start by getting the technician to run a calibration test. This should give you several exposure patches. The tech will choose the patch with the lines least visible.

 

[MacTwidget]

Adding to @Magnus59...
I think the focus is off and is only seen visually in the black because the screen is 45° and runs parallel to the laser direction.
Try plotting a plate with either the C, M or Y and change the screening to 45°. If you have the same issue, I would say it's focus.

 

[vance]

I'm afraid the tech is not here to run any tests, I am speaking with him over the phone to troubleshoot this issue.
He asked to change the 45 angle from black to magenta. So 75 on black and 45 on magenta. Now the problem is on magenta.

I am filming at 2540 dpi btw if that could be an issue.

I also think its CTP calibration needs to be done and focus ajusted. I printed the focus patches, but not sure what to look at. I will post a photo

 

[vance]

Here are the plates from the focus test, not sure what to look for. I have started at 1900 and intervals of 20 from left to to right. Currently i have set with 2540 dpi the focus at 2370

 

[vance]

Adding to @Magnus59...
I think the focus is off and is only seen visually in the black because the screen is 45° and runs parallel to the laser direction.
Try potting a plate with either the C, M or Y and change the screening to 45°. If you have the same issue, I would say it's focus.

the angle of 45 is having problems. He is a photo of my rip setting.

 

[ChrisZ]

Here are the plates from the focus test, not sure what to look for. I have started at 1900 and intervals of 20 from left to to right. Currently i have set with 2540 dpi the focus at 2370

You are far out of focus.

 

[vance]

You are far out of focus.

Please could you tell me where you can see it? I cant seem to see the difference..

These are the settings , seems odd all at 2000 except 2540

 

[ChrisZ]

Expose plate:
Initial value: 2230
Increment: 20
Count: 15
Start point: 10

And show me the plate. No need to put it on the press.

 

[vance]

Hi Chris,
Here is a photo. Let me know if you need a closer photo.
Thanks

 

[ChrisZ]

According to that image best coarse focus is 2390.
Put that value into 2540 field.
Than expose another plate
Initial value: 2320
Increment: 10
Count: 15
Start point: 10

Post a photo here, but try not to get light reflecting on plate for easier judgement.

 

[vance]

Here is the test plate. Thanks Chris

 

[ronniemanibo]

you can try this
Initial value: 2335
INcrement: 5
count: 23
start point: 10
it would give you a better look if you 2370 focus is really right

 

[vance]

Hello Ronnie, will try this. thanks all.