Riso GR 3750 pressure solenoid problem

[ianmck]

I recently replaced a worn pressure lever on my Riso GR 3750 where the solenoid hook kept slipping off. Now the solenoid hook does not activate most of the time. In test mode 68 it works fine though. I have videod the problem showing how the paper feed fails after a few cycles and the failure of the solenoid hook to activate after a few cycles (see below). More often than not the solenoid doesn't activate and the hook doesn't enage with the pressure leaver.
Does anyone have any suggestions as to what the problem mght be other than a faulty solenoid in need of replacement.

Thanks.

Ian

[Iowatech]

Re: Riso GR 3750 pressure solenoid problem

Actually, the pressure solenoid is activated unnecessarily most of the time and my first guess about why that is because there's not enough clearance between the pressure lever and the pressure hook at the top of their travel. There should be a millimeter of clearance then. That's actually pretty important, you should look into that.
Thanks for the video!

[ianmck]

Re: Riso GR 3750 pressure solenoid problem

Actually, the pressure solenoid is activated unnecessarily most of the time and my first guess about why that is because there's not enough clearance between the pressure lever and the pressure hook at the top of their travel. There should be a millimeter of clearance then. That's actually pretty important, you should look into that.
Thanks for the video!

I checked the clerarance and that is OK. In test mode 68 the hook tips forward and I guess thisis what it needs to do to engage with the pressure leaver, but it isn't. I wonder if the signal from the paper sensor isn't coming through consistently.

[20gaugeO/U]

Re: Riso GR 3750 pressure solenoid problem

The 2 wires to the solenoid used to break at the big looping bend in the middle. I can't tell if there is clear shield around the wires but if there is cut it off and stress pull the wires and see if they are hanging by a thread. Can always solder back together if they break.

Next would probably be the paper in sensor area. Nick in the paper feed mylar or the paper In sensor is failing. If you test the paper in sensor in service mode and it goes from fast beeps to slow beeps (change of states from detecting paper) that's good. But if you move the paper quickly under the sensor I used to be able to get a bad sensor to "wig-out" and do fast and slow beeps at same time. A couple fast beeps, then a slow one, then a couple fast, then a slow one -- with the paper removed.

Next check and see if the drum is spinning internally. That can cause weird timing issues if it isn't spinning as it should.

[ianmck]

Re: Riso GR 3750 pressure solenoid problem

The 2 wires to the solenoid used to break at the big looping bend in the middle. I can't tell if there is clear shield around the wires but if there is cut it off and stress pull the wires and see if they are hanging by a thread. Can always solder back together if they break.

Next would probably be the paper in sensor area. Nick in the paper feed mylar or the paper In sensor is failing. If you test the paper in sensor in service mode and it goes from fast beeps to slow beeps (change of states from detecting paper) that's good. But if you move the paper quickly under the sensor I used to be able to get a bad sensor to "wig-out" and do fast and slow beeps at same time. A couple fast beeps, then a slow one, then a couple fast, then a slow one -- with the paper removed.

Next check and see if the drum is spinning internally. That can cause weird timing issues if it isn't spinning as it should.

Thanks for those suggestions. I'll have a look in a couplke of days when I have some time.

[ianmck]

Re: Riso GR 3750 pressure solenoid problem

Thanks to all. I re-checked and adjusted the timing properly and things have improved. Now if I can only solve the master removal problem....

[Iowatech]

Re: Riso GR 3750 pressure solenoid problem

Where does the old master get stuck?

[ianmck]

Re: Riso GR 3750 pressure solenoid problem

It isn't lifting off the drum. I have replaced the master removal hooks as one was broken. There's been some improvement with correction of the timing as it does now occasionally remove a master successfully, but more often than not I end up taking the drum out to remove it manually.