Riso GR3770 uneven print / pressure roller issue ?

[Teethevee]

Hi I'm new to the forum and just recently obtained a RISO GR 3770 duplicator. The duplicator had been sitting unused for at least two years and all the drums were dry. After cleaning a bit with alcohol and running a few hundred prints I got one of the drums making pretty good prints, but still there is an area of uneven print in the middle of the paper that goes all the way from top to bottom (picture attached) I tested it with another drum and the print had a similar effect, so my uneducated guess is that this could be an issue with the pressure roller ? I tried to clean the pressure roller with alcohol but it didn't affect the quality of the print. Can I solve this problem by changing a new pressure roller ? and if so, are there good instructions available how to do it ?

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[NeoMatrix]

If other drums are doing the same fault :
You could try carefully cleaning the thermal print head in the master unit.

[Iowatech]

If other drums are doing the same fault :
You could try carefully cleaning the thermal print head in the master unit.

If that pattern shows up on the master anyway, which based on the information shared so far it almost absolutely will.
Along those lines, you might want to check your master material to make sure it doesn't have that defect already built in. That's a pretty old machine after all.
If you haven't tried resetting them machine already, I'd try that first though.

[Teethevee]

Many thanks for your answers. I'll try to clean the thermal print head this evening and see if it has any effect. Master roll came with the machine, it was still wrapped before I put it in the machine, but I have no idea how old it is. How do I reset the machine ? I couldn't find the right info in the manual or online.

[VENRISO]

try to change the drum body and the screen.They sold on ebay for very good price.

[Woxner]

being this old i think its the press roller either deformed or clean it with wd40. seen this many times. print head would be more fine lines.

[Iowatech]

How do I reset the machine ?

Turn the machine off, then hold down the "Reset" key while turning the machine on, and continue to hold the key down until the initializing motors quiet down.
I was kind of hoping you'd search for that in the CTN digital duplicator forum so you'd get a feeling of years of information for the GR series already here. You'll find it quite useful the longer you have that machine.

[Teethevee]

Today I cleaned the pressure roll with WD-40, also cleaned the thermal print area, and reset the machine. I had actually reset the machine also before, but wasn't sure if I did it right since the machine gave me no sign that it was reset. Any of these didn't help, the print stayed the same. In the attached image you will see how the first print looked with the other drum. If I make 20 more prints the middle of the print gets darker, but its still visible. (the unprinted area in the top of the print is because of dry drum, the other drum prints good all around, see previous image)

Since the machine is making the same kind of uneven print with different drums I guess it's not the drum that is causing this. I think it must be the pressure roller. I will order a new pressure roller and a new master roll, just in case the master roll has gone bad somehow.

I've been going through the posts regarding Risos in the duplicator section of the forum and really learned a lot. Already managed to solve a problem with wrinkled master Also found the necessary information how to clean the drums and managed to get the machine working! the previous owner had given up already...

Nevertheless I couldn't find info on how to actually take out the pressure roller and put a new one back in, I would be very thankful for some experienced advice on this. Here's a picture of the pressure roller after I cleaned it with WD-40 and made a few prints. Does it come out by taking out the screws on both ends of the pressure roller?



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[Woxner]

look at the front bearing of the press roller. there is one screw that holds it in. remove and pull forward on the roller. just make sure when reinstalling to get back bearing seated. to clean this good it would have been best to remove. since this is so old i imagine the press roller could be indented from paper.

[Iowatech]

IMG_0139.JPGIMG_0137.JPG

Thanks for the pictures.
The first one makes it appear that you are not running enough prints per master. Under normal circumstances, you should run no less than twenty prints per master, and from a service standpoint the very least you can run is ten prints.
The second picture may indicate an image registration issue, but more often than not that is caused by the paper you are trying to print on being shorter that the image on the master.