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Thread: GR3770 Troubles

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    GR3770 Troubles

    Hey there,

    I recently acquired a Risograph GR3770 from an office in town that was downsizing. I'm having trouble with a few things, and after digging through a good amount of posts (thanks to copytechnet.com) I feel I've a basic understanding of the machine. However, after tinkering for a week I'm still having trouble.

    The machine is jamming up pretty much every page I try to print. The paper gets stuck under the color drum, no where else. Every so often I do successfully get a page through, however the registration is usually very out of whack and sometimes "ghosting" is left behind.

    I made sure all of the disks were aligned according to the tech manual but I'm still experiencing the same problem..

    Any ideas? I can take images of any part of the machine, just let me know. Thanks in advance for any help!

    IMG_3731.JPGIMG_3732.jpgIMG_3733.jpgIMG_3734.jpgIMG_3735.JPG


  2. #2
    Senior Tech 250+ Posts 20gaugeO/U's Avatar
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    Re: GR3770 Troubles

    When it does pass a piece of paper is it centered in the right spot on the page?

    Your second pic. The disk is in the right spot but can't see the timing mark that is behind the disk in the 4 o'clock position. Is it in time also? As well as the feed clutch itself. Can't tell what style it is. There was a spring style (bad), then the good old disk style (good) and the best of all the big gold clutch (which you don't have).

    Some of the necessary feed parts are no longer available from Riso and haven't been around for a while. Just so you know


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    Riso dude 250+ Posts jermyth's Avatar
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    Re: GR3770 Troubles

    Sounds like its out of time/ registration off hence the image issues. I believe this had been discussed here before. PM me if you need a better clutch.
    Good luck.


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    Re: GR3770 Troubles

    20gagueO/U, thanks for the tip! I must have missed the cam pulley when I was aligning everything initially. I released the tension on the paper feed clutch, aligned the holes on the cam pulley and main shaft plate, and the machine no longer jams! Registration isn't perfect yet and it still looks like there's some extra ink / ghosting at the bottom of the print, any clue what could be causing this? (I understand registration isn't ever going to be perfect but the image should be centered more or less, no?)


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    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: GR3770 Troubles

    As far as the ghosting goes, if that also happens on the back of prints it could be the image is too long for the size of paper and the registration of the prints. You might try increasing the blank area on the trailing edge of the original you are trying to print.
    If the registration is consistently off by a half inch or more, you can try adjusting the drive belt on the pulley behind the disk in picture two by one tooth in the direction you wish for the image to go on the print paper.
    If the registration is consistently off by less than a half inch, that will probably be tough.
    In theory, you just have to loosen the screws in the three o'clock and nine o'clock positions behind the disk in picture two, then rotate the cams in the direction you wish for the image to move on the paper.
    In practice though, even when the GR series was new, those cams would seize to the drive shaft they are installed on, and were very difficult to break free.
    (In case you are more comfortable with metric measurements, one half inch equals 12.7 mm. Been a while since I've had to do that conversion, but if I remember correctly it has a tolerance of plus or minus 0.006 inches, so it should be pretty close.)


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    Re: GR3770 Troubles

    New problem: Looks like there's a bit of a problem with the paper feed. Multiple pieces of paper are being picked up every so often, sometimes resulting in a jam. I removed the pickup roller and cleaned it with isopropyl but I'm still having trouble. This also throws off the registration a bit so I'm concluding these problems are connected. Is there too much upward pressure on the paper? Should I be cleaning any other parts?


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    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: GR3770 Troubles

    Quote Originally Posted by admgreen View Post
    New problem: Looks like there's a bit of a problem with the paper feed. Multiple pieces of paper are being picked up every so often, sometimes resulting in a jam. I removed the pickup roller and cleaned it with isopropyl but I'm still having trouble. This also throws off the registration a bit so I'm concluding these problems are connected. Is there too much upward pressure on the paper? Should I be cleaning any other parts?
    It is more likely that the rubber pad that is responsible for insuring one sheet of paper is fed at a time is to blame for this. And it could simply be out of position for the type of paper you are using. There should be two green knobs in the area where you load paper that will adjust that rubber pad. The proper adjustment of those knobs requires patience and creativity, but try that first before you go any further.
    Also, if possible, avoid using alcohol to clean rubber rollers. Alcohol will dry out the rubber, which often leads to premature roller failure.

    Last edited by Iowatech; 08-31-2014 at 04:44 AM. Reason: There's no "f" in the word "it".

  8. #8
    Senior Tech 250+ Posts 20gaugeO/U's Avatar
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    Re: GR3770 Troubles

    Ya what Iowa said. But just to add a bit to this
    "In theory, you just have to loosen the screws in the three o'clock and nine o'clock positions behind the disk in picture two, then rotate the cams in the direction you wish for the image to move on the paper.
    In practice though, even when the GR series was new, those cams would seize to the drive shaft they are installed on, and were very difficult to break free."
    -- If the screws are loose and the cam won't move, you can take a flat head screwdriver and tap the cam. Sometimes they move great and others will only move a bit. If it moves you have to tighten screws back up and test a few copies. All trial and error.
    You might think about getting a new set of FT and sep pad if they are old. I never had much luck with the generic ones either.
    In your 5th pic the right dial arrow should be pointing at the screw that's at about 11 o'clock for 20lb paper to start. And I can't tell the color of the feed tires. If they are blue get rid of them.
    Good luck.


    Last edited by 20gaugeO/U; 09-02-2014 at 04:50 PM.

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    Re: GR3770 Troubles

    Thanks so much everyone. I was able to rotate the cam and get the vertical alignment pretty close to perfect. 20gague, my tires are indeed blue. Should I definitely pick up new ones? The screw on the right is at around 3 oclock and the multifeeding issue isn't happening nearly as much as before. If it's set at 11, a good 10 sheets are picked up at once causing the machine to jam. What color tires should I be looking for? I found black ones on ebay that were reasonably priced.

    Thanks again for all the help.


  10. #10
    Just a fellow wanderer 2,500+ Posts Iowatech's Avatar
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    Re: GR3770 Troubles

    The black tires should work OK if they are from Riso. I don't think they've been made in a while though. But if the "fins" on the tires are at least still mostly triangular the tires should be OK.
    The newer gray tires have worked pretty well for me, even on the couple of GR machines I still see.
    (Heh, for a little while we used the feed roller assemblies from the TR/CR line, it took a bit of "engineering", but it worked great. It was also significantly more expensive than just replacing the tires, so that came to an abrupt end.)
    If you do replace the tires, make sure the rubber pad underneath the inner roller assembly isn't worn too bad. Also, there were multiple colors of pads available for the GR line, which the best I found was the green pad followed by the yellow one. If the rubber pad doesn't look too bad, clean it off with some soapy water and it should be OK.


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