MZ790 Horizontal print position / second drum print school

**mixedfeelings** · 10-23-2014

Hi All -
I have finally been fixing up and aligning an mz790 and I have run into a couple of problems:

Horizontal print position:
All masters are created with the horizontal position 1/16" - 3/32" to the right. I have tried adjusting the horizontal drum / main position using test modes using test modes 973 (drum) and 974 (machine) to no avail. Is there a way to change the center position of the TPH as there was with the RP models?

Second drum skew
The master has a clockwise skew, but is not substantial. I used the slide shaft to compensate for it and I got close - but i ran out of room to slide it any more - it's right to the edge. I have tried multiple drums, and swapped the drum positions and the first drum is always pretty good, but the second is always a little skewed. Are there other options besides the slide shaft? Is there a way to adjust the feed between the two drums? perhaps that path is where its going awry?

Thanks!

**Iowatech** · 10-24-2014

Pictures, please?

**mixedfeelings** · 10-26-2014

Hi Iowatech! I would gladly take a picture - what do you want to see?

Thanks!

**Iowatech** · 10-27-2014

Well, if you could pull the drum out after it made a skewed master and take a picture of the top of the drum cavity, that would be a good one. A picture of the skewed master on the drum or a print from one of them would be helpful too. And if you could open up the master making unit like you were going to load a new master roll, and take a picture of the master material being fed into the unit, that would also be helpful.

**mixedfeelings** · 02-02-2015

Sorry I never posted images - in the end, I think that my problem stemmed from the master making unit being off by a tooth. Once I realigned the unit, I was able to work within the margins of the slide shaft adjustment. It's not perfect but its better!

It has revealed another issue with skew on the drums themselves. To test, I am making all of my masters in the first drum position and some drums go on reliably straight while others go on reliably crooked. Is there a drum level adjustment for this?

Another related issue is that masters on drums in the second position start out straight and then begin to skew very quickly - by the 30th impression there is about a 2-3º clockwise skew. I know that masters travel a little over time but that level of skew that quickly seems a little extreme. Could it be a loose master clamp? the pressure roller?

Thanks!

**jermyth** · 02-02-2015

Second drum position having masters getting skewed could be from the impression roller having uneven pressure on the drum. Does it happen with all drums used? I believe the adjustment for the pressure roller is in the manual, personal haven't had to do it.
Good luck.