I have some bad news for you. It can't be fixed.
I tried for 6 months straight. 4 techs from my dealer and 2 techs from Roland flew out and could not figure it out. The reason they couldn't figure it out is because it's a flaw with the printer itself. They were all set to replace my FT with their demo, but a light clicked in their heads and they tried to print black on their own demo and it produced identical results. Only then did they agree to return it outright.
After hundreds of hours of troubleshooting I've found a few less than ideal work arounds to help mitigate the vertical banding.
1. Print in White + CMYK mode but with no white layer. This mode is the only mode that will allow a head speed of 1000 mm/s. That combined with the obscene amount of passes, it essentially eliminates the banding. Unfortunately this mode will triple or quadruple your print times. In our case, we always overprint 2x or 3x so you can see why this isn't a viable long term option. A 4x8 panel with 2x overprint takes roughly 5 hours to print in this mode.
2. Only print your blacks with K. Spot color BK21a. This usually works because the banding is caused by the mixing of colors which haven't been properly calibrated for the lamps on the 640 so it produces gloss vertical banding. Using only the K channel reduces the effect considerably. However, because this printer also has issues with starvation, you may find (like we did) that it isn't capable of printing black with just K for long before you start getting really bad horizontal streaks through your prints.
3. Unplug the right (trailing) UV lamp. This is a solution I tried around month two. While it does help with the vertical banding, it makes the print very gloss from not being cured correctly and hurt the adhesion to plastic so I didn't find this viable. Amazingly months later, Roland finally came up with a "solution" and sent me instructions. Low and behold it was merely unplugging the right lamp, essentially rigging the machine. Another reason this isn't viable, which they apparently didn't take into consideration when creating this solution, is that it requires you to be in service mode since unplugging the lamp will produce an error upon startup and while in service mode your printer will never turn off (sleep) and wont run auto cleaning cycles. Roland brilliance in action.
Note: I don't recommend doing this unless you know the process. You can PM me and I can send you the instructions if you want.
4. Print in high speed. It's backwards thinking but printing in this mode will actually produce other more subtle print defects like horizontal banding that will help mask the vertical banding. This is how we printed just about all our solid colors.
5. Use high head height. It may seem counter intuitive but the increase height masks the banding. Unfortunately this will also make the detail in your prints look like hammered dog **** but for large solid colors it does help.
6. Get a new printer. You might think I'm joking but really I'm not. I spent hundreds of hours and countless late nights/weekends dealing with that god forsaken machine and sent dozens and dozens of emails to Roland throughout the process and got exactly zero help in return short of techs coming out to patronize me as if I somehow was imagining all the problems I had. Thankfully my dealer was on my side and was able to get it returned.
The Oce we replaced it with has been here for two weeks and I can honestly say it's night and day. It was significantly more expensive but I'm extremely happy with it so far.
7. Don't print solid colors. lol.
Things that will
not help.
-It's not static - I cannot stress this enough. I tried everything from static bars, dryer cloth, humidity control, static cleaners....nothing. Don't let anyone feed you this crock of BS.
-Higher quality - As you've probably already figured out, increasing to high or even artistic will not help you. The higher the quality can actually make it worse because there are less perfections to mask the banding.
-Uni directional - The problem occurs identically in both modes.
-Roll Vs. Rigid - Both will produce banding. One just uses a higher head height than the other.
-Nothing in the service menu - You might be tempted to tool around in there to see if there is anything that will be of help. Don't waste your time. There is nothing to address the issue there.
-Editing profiles - I spent a lot of time tinkering with different profile adjustments. Reducing certain colors, increasing others. None of them work.
-Changing Versaworks settings - All the quality, profile, halftone, color management don't solve the problem. Nor will different file formats or Illustrator settings. I tried every combination of every settings. All with the same result.
-Adjusting the belt tension - This is Roland's go to for this problem. I **** you not we had 4 techs out here to "adjust" the belt tension because "it worked for somewhere else." No, it doesn't work and it took them 2 -months of tinkering with the belt to figure that out.
Hope that helps. Sorry to be the bearer of bad news.
