Riso/Risograph RZ 990 - Lines on Prints

[samraisenz]

Hey Good Folks,


1-2 faint lines are on my prints. Images attached. I'm wondering if anyone has any thoughts on what might be causing them. Here are some observations:

• The lines appear on every one of my drums, black and 8 color drums.
• The lines appear in the same place on every page no matter the color. This leads me to believe this isn't a case of "drying ink" on any particular drum. I'm using genuine RISO ink.
• I've thoroughly inked every drum. They were all recently pieced apart and cleaned and put back together. The ink is still within the expiration timeline.
• I do not believe this is a case of improperly prepared files. I've tried different images, patterns, test prints. Doesn't matter if an image is 100% Ledger sized or Letter size -- the lines appear on the same place on the page.
• Lines appears when printing from USB connected AND from flat-bed scanning.
• I have thoroughly cleaned the pressure roller of any ink using a microfiber rag and denatured alcohol.

I want your thoughts on what it might be. Additional thoughts (subject to question:

• Thermal Print Head? I'm skeptical because the lines aren't super well defined. I've read elsewhere that issues with a damanged/burnt TPH create well defined, sharp lines. These lines are visible, but not sharp.
• The Pressure Roller was (somewhat) recently replaced. Granted, it was an after-market manufacturer (bought from eBay, shipped from China). It's within a year of being replaced. However, it's tough to rule out that maybe there's a tiny defect on the roller.
• When I remove the master from the drum, I can't see the line burned into the master. It's so thin and faint, I can't tell if it's a defect with the master or something else.

Possible Solutions:

• My first bet is to replace the pressure roller. Easy enough to find replacements. Relatively cheap enough.
• Replace the TPH. Expensive, difficult, time and cost intensive. If it is the TPH, I'm just going to live with this, but that isn't great. As far as defections in prints go, I could be stuck with worse.
• Live with it and accept that this is the way it is now.

[jermyth]

I do not think it's the TPH, that gives you solid line(s). It looks like a void line to me. Are these images from a scan off the glass or a direct print job? If scan then try cleaning the optics. If prints, then try cleaning the drum screen and maybe drum shell too. It's possible something in the squeegee assembly causing no ink to fill in the area.

Good luck.

[samraisenz]

Thanks, Jermyth.

The prints pictured have been via direct-print (USB). The lines have also formed when Flat bed Scanning. Tried both. Same error on both. I'll give the optics a (gentle) cleaning and see if that does anything. Another friend said to check the connections. Disconnect then reconnect, that might help?

My gut tells me it isn't a drum issue because it's in the same place on *all* the drums. No matter what is printed/scanned/zoomed in/zoomed out. Same place on the paper. I suppose it's unlikely that all 8 drums have the same defect in the same location on the drum, but It isn't impossible. Granted, it does appear that is where one of the ink distributor openings empties out onto the squeegee roller. If i cant find a good solution, Ill open one or two drums up and see if clearing that spot does anything.

I'm going to try flipping the pressure roller. If the same line flips along the horizontal axis, I'll know there's a defect in the pressure roller. If it stays in the same spot, it must be drum-related, optics/t-head, or something else. More to com.

[jermyth]

If you have a defect on the impression roller, a groove, then the impression roller would not be touching the paper in the spot and you won't get any ink on the paper. So that is a possibility. If it's happening on all drums, i highly doubt it's a drum issue too.

Good luck.

[samraisenz]

Small Update:

• Flipped the Pressure Roller -- the line(s) were still in the same place. So it isn't a defect on the pressure roller.
• I wrapped a drum in a confidential master (so no ink would get through), and folded the lip under the clamp and taped it down. Then wrapped another master on top of that one. Upon closer inspection, the burned master has the faint lines burned into it.
• Leads me to believe this is an issue with the Master Making Unit in some way/shape/form. Including, but not limited to the Thermal Print Head, though the defect isn't quite as sharp as an issue with the TPH would be.

More to come later. It might seem wild, but I've got a strange feeling I've got a small shred of master/debris somewhere inside the Master Making Unit that's stuck and interfering with how the master is burned.


Appreciate the insight, jermyth.

[jermyth]

Sounds like you got something on the TPH. I had that happen YEARS ago. Wow, bad memories. Look at the TPH, it should be uniform all across it. Try wiping the TPH with a soft dry cloth.

Good luck.