RISO GR3770 - First paper feed problem

[Cp31]

hello all,

im writing because i have a recurring issue with an old GR3770.

most of the machine runs just fine, but the first paper feed (scraper/pickup rollers) is giving me headaches.
it is not picking up paper, the wheels do not spin. the paper feed clutch engages just fine, and rotates normally, however the movement is not transmitted to the pickup shaft/to the wheels properly.

i can get paper through by running test mode 107 (continuous paper feed) multiple times : the wheels sometime spin just a little bit, and eventually end up pushing paper to the second paper feed - at this point the paper is picked up just fine and runs through.
whats odd is that this behavior sometimes disappears for a time (running test 107 has "unlocked" the wheels before), and then reappears randomly.

the timing of the machine is fine. the paper feed clutch runs normally and print registration is ok.
adjusting the pressure dials does not fix it.
i also tried readjusting the height of the elevator top position sensor and apply less/more pressure, it did not get the wheels spinning again.
im not sure what to look at or for, but from what i see there is nothing physically blocking movement.
could not get anything on this from the tech manual.

how can i check at which point in the assembly movement stops being transmitted ? im not sure what to take appart.

maybe its the bearings inside the rollers ? the outside/rubber part does not seem to be worn out and their teeth feel pretty sharp. i tried spinning them by hand, i felt like they where hard to get moving, should they be spinning freely ?

thanks for reading and for your help !

[Peacepunk]

THat's weird, if the clutch engages then it MUST also move the pickup shaft and the wheels, otherwise that would mean it does not engage. I would suggest check the clutch again/clean it and also check the P-disc Sensor.
The other thing could be the stripper pad braking the second wheel, but it would mean the clutch doesn't engage enough to force the wheel spinning

Good luck!

[Peacepunk]

Another thing that could be at fault here is the stack paper switch; try to push down the stripper pad with your finger and listen if you hear a "click" after pushing it down about 1 mm. If you don't hear it, or you hear it right away, try to remove the stripper unit and lower the sensor/switch a little bit.
The switch basically disengages the clutch in case there is too much paper between the rollers and the stripper pad to avoid misfeeding of too many sheets.
Also, speaking of the clutch: check that the pickup roller shaft is correctly mounted and that the connection with the Paper feed clutch shaft is good!