Riso MZ 790U – Master Sticking on Black Drum

**benchpressprint** · 07-31-2014

Hey guys,

I've been having a problem lately with the black drum (copy count: 777,534) on my Riso MZ. When I try to make a new master, the machine tells me that the master is stuck in the master disposal box and to remove it, which it isn't, and then that I need to manually remove the master. After a few goes of this, it eventually makes a new master but sometimes the previous master is partly ripped and still stuck to the drum underneath the new master. I've attached a photo of what it looks like when I pull the drum out to remove the master like the machine asks. It's happening on both sides of the MZ and only with my black drum. I recently replaced the 'master disposal belts' (rubber bands) on both sides of the machine thinking that it might be a problem with those but that hasn't seemed to help. Somebody suggested in another thread for a similar problem to try cleaning the clamp plate and clamps and to lubricate the pivot points, which I did, but that hasn't seemed to help either. I've also noticed that the black ink is causing the masters to yellow quite a lot, which I hadn't noticed before unless the masters were left on the drum for quite a long time. I always use OEM inks and masters too. Does anyone have any ideas of what the problem might be and how to fix it?

Thanks in advance!

Dan

Photo 31-07-2014 10 57 47 pm.jpg

**jermyth** · 07-31-2014

This problem killed me for a while with replacing the clamp plate assembly on multiple drums. Finally a coworker found that the ejection plate was sticking to the base of the assembly. What's happening is the ejection plate is not flipping out the master enough to get into the disposal unit. I bet if you look carefully you will see a nick from the ejection plate slamming back to the base. Use a cutter or grider and remove part of the base that its sticking to. I can post a picture or two later if you'd like.
Good luck.

**Iowatech** · 08-01-2014

Originally Posted by jermyth

This problem killed me for a while with replacing the clamp plate assembly on multiple drums. Finally a coworker found that the ejection plate was sticking to the base of the assembly. What's happening is the ejection plate is not flipping out the master enough to get into the disposal unit. I bet if you look carefully you will see a nick from the ejection plate slamming back to the base. Use a cutter or grinder and remove part of the base that its sticking to. I can post a picture or two later if you'd like.
Good luck.

I was going to say probably one or more of the white nylon rollers in the clamp area were broken, but I like your answer a lot better.

**gillje** · 08-01-2014

Since you mention that the masters are yellowing, I would think it might be a problem with the ink you are using / whatever's leftover in the drum. I recently had a black mz drum where the first half dozen times I would try to use it I would have this exact issue - yellowed, slightly greasy master, stuck or torn on the drum. Once I replaced the tube that came in the drum with a fresh, non-expired tube, and got some of that ink running through the drum, this problem totally disappeared.

**LA TECH** · 08-02-2014

I had that problem before, and the culprit was the ejection plate on the drum itself, I could bent a little not permitting to open all the way up. Resulting in master diposal jamming.

**benchpressprint** · 08-04-2014

Hey guys,

Sorry for the slow reply and thanks for the suggestions!

Originally Posted by jermyth

This problem killed me for a while with replacing the clamp plate assembly on multiple drums. Finally a coworker found that the ejection plate was sticking to the base of the assembly. What's happening is the ejection plate is not flipping out the master enough to get into the disposal unit. I bet if you look carefully you will see a nick from the ejection plate slamming back to the base. Use a cutter or grider and remove part of the base that its sticking to. I can post a picture or two later if you'd like.
Good luck.

I looked at the drum and tried comparing it to another drum that's still working but couldn't find anything like nicks on the clamp plate assembly. I could be looking in the wrong place or for the wrong thing though. If you wouldn't mind posting some pictures, I'd really appreciate it!

Originally Posted by gillje

Since you mention that the masters are yellowing, I would think it might be a problem with the ink you are using / whatever's leftover in the drum. I recently had a black mz drum where the first half dozen times I would try to use it I would have this exact issue - yellowed, slightly greasy master, stuck or torn on the drum. Once I replaced the tube that came in the drum with a fresh, non-expired tube, and got some of that ink running through the drum, this problem totally disappeared.

In order to see if it's expired ink that's the problem, I'd have to run off a lot of prints to flush out all of the old black ink, huh? I put a new tube of OEM ink in and ran off about 20 solid black prints. I'll see how yellowed the master is tomorrow and maybe try to flush out more old ink.

Cheers!

Dan

**jermyth** · 08-04-2014

First image is the clamp before modifying it. I have lifted up the ejection plate to reveal the scratch marks on the clamp base.

Second image is after I have cut the base where the ejection plate was sticking.