[Electrical] Riso MZ790 - Master Removal Malfunction

[unwork_inc]

I'm seeking advice in fixing a Riso MZ790UI which has stopped removing the masters from the drums. This happens on all drums, on both positions.

I removed and thoroughly inspected both Master Removal Units, as well as First and Second Clamp Units, and everything seems to be in place, no broken parts or disturbed mechanics. I've replaced all master removal belts and cleaned up and refreshed all rollers, but nothing changed.

I then swapped all these components with those from a perfectly working MZ790UI, but the problem persisted, while the donor machine worked fine using the components from the broken machine.

This led me to think that the problem might be electronic or software-related, perhaps some calibration that needs to be adjusted. But the machine shows no errors whatsoever so I'm not sure what setting to modify.

I gladly welcome any tips related to the master removal operation which might bring me closer to finding out what's wrong with this machine.
Thanks in advance.

(I'm attaching a few images of the components mentioned here)

Screen Shot 2021-05-04 at 7.20.50 PM.jpgScreen Shot 2021-05-04 at 7.20.45 PM.jpgScreen Shot 2021-05-04 at 7.20.19 PM.jpg

[jermyth]

Re: Riso MZ790 - Master Removal Malfunction

Have you tried watching the action of the master removal via cheating the door switch and looking too see where and when the failure occurs?
Good luck.

[ntbann]

Re: Riso MZ790 - Master Removal Malfunction

Are the masters wadding up at the disposal box entrance? If so you may have a drum alignment issue.

[unwork_inc]

Re: Riso MZ790 - Master Removal Malfunction

Thank you for your reply jermyth - Yes, I did observe the master removal action on both drums by tricking the door switch open, but couldn't see any possible malfunctioning. I even shoot a slow motion video with my phone on both machines in order to compare the master removal process on the working and the non-working machine, but the action seems identical on both.

[unwork_inc]

Re: Riso MZ790 - Master Removal Malfunction

Thanks for chipping in ntbann - The masters are not being removed at all from the drum. They remain on the drum with the leading edge still under the master clamp plate, slightly bulged up after the master ejection plate tries but fails to remove it.

[ntbann]

Re: Riso MZ790 - Master Removal Malfunction

I had one once that the drum drive gear screws loosened up in the drive pack (back of the machine) causing master removal problems. Had to use the alignment pins to retime drive and tighten screws back down.

[unwork_inc]

Re: Riso MZ790 - Master Removal Malfunction

I had one once that the drum drive gear screws loosened up in the drive pack (back of the machine) causing master removal problems. Had to use the alignment pins to retime drive and tighten screws back down.

Thanks for this info. I didn't inspect the drive pack, I'll take a look into it. I'm assuming it's properly dialed in because the machine loads masters and prints just fine, but I'll take a look and see if anything seems out of tune.

[unwork_inc]

Re: Riso MZ790 - Master Removal Malfunction

I looked into the drive pack and overall inspected the whole drive mechanism from the back of the machine and didn't find anything unusual.

What did seem to help is replacing one of the plastic actuator on the first clamp unit attached to the master making unit. I've found a spare part of this actuator, along with one of its gears, swapped them with the ones that were in the machine and it seems to be working, the machine removes masters at both positions now the way it should.

What's curious is that neither the spare actuator nor its gear seem to be in any better shape than the ones in the machine. In fact, they both look more worn out. But it's working for now and I'm fine with that. I'm attaching a picture of the actuator I replaced, along with videos of the master removal process in case it helps someone else.

One thing I noticed is that when the clamp plate hits the first clamp unit in order to release the leading edge of the master, the master making unit (onto which the first clamp unit is attached), is slightly bumped forwards by the force. This seems natural and shouldn't present any issues on a new or properly dialed machine. But on old and used equipment, it may cause the master ejection plate to bounce against the plastic plate attached to the bottom of the master making unit, preventing it from lifting the master all the way out from under the clamp plate. This could be the reason why masters are not being removed and appear 'bulged up' at the clamp when removing them by hand. Next time I get I there I'll look into what kind of stoppers the master making unit has and make sure they are in good shape in order to minimize this bumping forward. Another thing to check in combination with this, is the Print-drum Position-A adjustment (test mode #941), which may affect the position when the clamp plate hits the first clamp unit, subsequently affecting the time when the master ejection plate is triggered, failing to pull the leading edge of the master all the way out and onto the master removal belts.

https://streamja.com/A0ePk

https://streamja.com/P3e9z

https://streamja.com/OnezX

[unwork_inc]

Re: Riso MZ790 - Master Removal Malfunction

<font color="#333333">I looked into the drive pack and overall inspected the whole drive mechanism from the back of the machine and didn't find anything unusual.<br>
<br>
What did seem to help is replacing one of the plastic actuator on the first clamp unit attached to the master making unit. I've found a spare part of this actuator, along with one of its gears, swapped them with the ones that were in the machine and it seems to be working, the machine removes masters at both positions now the way it should.<br>
<br>
What's curious is that neither the spare actuator nor its gear seem to be in any better shape than the ones in the machine. In fact, they both look more worn out. But it's working for now and I'm fine with that. I'm attaching a picture of the actuator I replaced, along with videos of the master removal process in case it helps someone else.<br>
<br>
One thing I noticed is that when the clamp plate hits the first clamp unit in order to release the leading edge of the master, the master making unit (onto which the first clamp unit is attached), is slightly bumped forwards by the force. This seems natural and shouldn't present any issues on a new or properly dialed machine. But on old and used equipment, it may cause the master ejection plate to bounce against the plastic plate attached to the bottom of the </font><font color="#333333">master making unit, preventing it from lifting the master all the way out from under the clamp plate. This could be the reason why masters are not being removed and appear 'bulged up' at the clamp when removing them by hand. Next time I get I there I'll look into what kind of stoppers the master making unit has and make sure they are in good shape in order to minimize this bumping forward. Another thing to check in combination with this, is the </font>Print-drum Position-A adjustment (test mode #941), which may affect the position when the clamp plate hits the first clamp unit, subsequently affecting the time when the <font color="#333333">master ejection plate is triggered, failing to pull the leading edge of the master all the way out and onto the master removal belts.<br>
<br>
</font><a href="https://streamja.com/A0ePk" target="_blank">https://streamja.com/A0ePk</a><br>
<a href="https://streamja.com/P3e9z" target="_blank">https://streamja.com/P3e9z</a><br>
<a href="https://streamja.com/OnezX" target="_blank">https://streamja.com/OnezX</a>

[unwork_inc]

Re: Riso MZ790 - Master Removal Malfunction

(For some reason my last post appeared twice on the thread. If you are an admin please remove the duplicate post, found right above this one, as well as this very post. Thanks.)