Risograph GR3770 Master not sticking to drum et al

[Iowatech]

@Iowatech

Thanks. The small middle roller isn't spinning, but the big one at the bottom is. That roller on my other working drums spins so this must be the issue then huh. Any steps I should take to fix this?? Thanks!

Check the drive belt in the back of the drum to make sure it is OK. Also, one of the pulleys that the belt rides on kind looks like an idler pulley, but it actually drives a shaft that the ink bead forms around. I've seen that break a couple of times. You might check that, too.

[NONPOROUS]

Check the drive belt in the back of the drum to make sure it is OK. Also, one of the pulleys that the belt rides on kind looks like an idler pulley, but it actually drives a shaft that the ink bead forms around. I've seen that break a couple of times. You might check that, too.

Thanks again. I took off the plastic covering of the back and checked the belt w/o dismantling the whole drum. I'm comparing the broken drum to a working drum and everything seems to be functioning the same on both. The belt turns the small "drive shaft" from the outside looking through the back, but when I pinch the belt it doesn't spin as I look inside the drum thru the cartridge hole (it does rotate the driveshaft thing when I pinch the belt on the working drum). Very confused. Any further instruction would be great!

[Iowatech]

Thanks again. I took off the plastic covering of the back and checked the belt w/o dismantling the whole drum. I'm comparing the broken drum to a working drum and everything seems to be functioning the same on both. The belt turns the small "drive shaft" from the outside looking through the back, but when I pinch the belt it doesn't spin as I look inside the drum thru the cartridge hole (it does rotate the driveshaft thing when I pinch the belt on the working drum). Very confused. Any further instruction would be great!

I don't understand what you mean by "pinch the belt". Please elaborate.

[NONPOROUS]

I don't understand what you mean by "pinch the belt". Please elaborate.

Sorry, I mean I was playing with the belt, jiggling it a bit if you will. If I apply enough pressure it will move the other parts around as it should. The belt turns the thing connected to ink drive shaft on the outside, but it's not turning the actual drive shaft as I look in through the ink cartridge. Does that make sense?

[NONPOROUS]

Anything else that could be preventing the drive shaft from spinning?

[Iowatech]

Thanks for explaining the "pinch" thing.
If the ink bead isn't rotating when you move the belt around, the shaft that the ink bead forms on is probably broken. If that's the case, it might be best to use that drum for parts. The belt is one thing you will want to hold on to as every once in a while they break. Also, the pulley that drives the big roller in the drum is something to hold onto as well, it has a one way bearing that only allows that roller to rotate counter clockwise as viewed through the ink tube cavity. The bearing sometimes gets full of ink or separates from the pulley which will cause the big roller not to rotate at all.

[NONPOROUS]

Thanks for explaining the "pinch" thing.
If the ink bead isn't rotating when you move the belt around, the shaft that the ink bead forms on is probably broken. If that's the case, it might be best to use that drum for parts. The belt is one thing you will want to hold on to as every once in a while they break. Also, the pulley that drives the big roller in the drum is something to hold onto as well, it has a one way bearing that only allows that roller to rotate counter clockwise as viewed through the ink tube cavity. The bearing sometimes gets full of ink or separates from the pulley which will cause the big roller not to rotate at all.

Okay cool. Thanks for all your help. I have a problem that just happened to a different drum. It's inking but theres one almost perfect stripe that isn't. Do you know why this is happening, and how to fix?? Pic of the stripe: http://i.imgur.com/hEIDABC.jpg

Thanks.

[Iowatech]

Well, if the edges of the blank area were better defined, I'd say look for a strip of master material under the actual master on the drum. While I don't think that's the case, you might still want to check for that if you haven't done so already.
It could be that the ink bead is depleted in that area. As the ink on the other parts master in the picture look faded, that would be my first guess. The depleted area of the ink bead should be pretty easy to see through the ink bottle cavity if that's the case. If you see that, put a confidential master on the drum and run the machine until the ink bead in that drum is replenished.

[NONPOROUS]

Thanks for the insight - led me to some conclusions...so I realized that a piece of plastic had fallen into the drum (the plastic back covering came off). I fished it out but it still leaves the blank streak after running hundreds of sheets. Is it possible that the piece of plastic dented the inside of the drum slightly so that the squeegee can't make contact with the drum to push the ink thru??

[Iowatech]

Thanks for the insight - led me to some conclusions...so I realized that a piece of plastic had fallen into the drum (the plastic back covering came off). I fished it out but it still leaves the blank streak after running hundreds of sheets. Is it possible that the piece of plastic dented the inside of the drum slightly so that the squeegee can't make contact with the drum to push the ink thru??

That is somewhat improbable. Damage to the drum shell that would cause an image defect is pretty obvious, at least when I have seen it.
It's more likely that there is something blocking the gap between the squeegee roller and the silver roller in the area that corresponds to that streak. Or there is still something where you found that piece of plastic. There should be an area on the squeegee roller where you can see a lack of ink if that's the case (it might not look like much, but it will be there).