GR3770 - black and color drum won't print synchronized

[risobelgium]

Hello risographers,

I have 6 color drums that print at a certain starting point on the paper.
I have 2 BW HD drums that print with 10 mm offset.

As you may imagine, two color is very tricky with such an offset.

I thought my first black drum was worn, so bought the second one which prints at the same place.

So I guess the riso as a wrong parameter when it detects the drum (color or BW).

Hope somebody here can help!

Thanks in advance,

Pierre

[Iowatech]

Sounds like the drive coupling on the back of black drums are worn out.

[risobelgium]

Dear iowatech,

Thank your for your reply. My tech english is quite poor, sorry for that.

Don't you think it's strange that the two black drums have exactly the same problem? And that this problem is very stable (I mean, all sheet on both black drums have same offset).

Do you have an idea of a fix? Isn't there a parameter (in test mode?) that could tell the riso to print in black with another offset?

Thank you again,

Pierre

[20gaugeO/U]

Pull out drum that is in machine and set it aside. Look at the back wall of the machine and there is a large pin. Grab it and shake it left and right- it shouldn't have any "play" in it. If it has a little there is a crack in the roll pin inside that drive mechanism, a lot of play means the roll pin is shattered. From what you describe this isn't your problem just a heads up.

Now look at the rear of the drum where this pin should go. Take a good sized flat head screwdriver and see if this "slotted chuck" moves left to right as the drum stays locked in the home position. Any sloppy play means the 2 allen screws have backed out in that drive mechanism and needs to be tightened. That "chuck" should have the small notch at 12 o'clock and the larger opening at 6. Any little bit off moves the registration on each individual drum. Usually the black drum is the zero reference and each color drum is a little bit off. That's what the print position key is for. To fine tune each drum at needed when running multiple colors.

There is no test mode to adjust. These machines are old school mechanical.

A manual will help with this.

Good Luck