From: http://h30499.www3.hp.com/t5/Printers-Designjet-Large-Format/Double-Lines-being-Printed-Designjet-500/td-p/1091490?notmigrated#.VcVVSXFViko
Re: Double Lines being Printed - Designjet 500
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02-01-2010 08:46 PM
Here's my solution to the common double printing, blurred images on the Designjet 500 & 800.
When the carriage was removed to install a new belt, I had also removed the two "C" shaped bushings as well, one on each side of the carriage. I didn't need to, but thought I could get the carriage off without removing the right-hand side cap and service-station... BTW, you DO need to.
Anyway... when they were reinstalled, they were swapped accidentally left for right (they only go in one way) and they fit pretty loosely in the carriage when they are swapped.
The resulting slop will allow the carriage to "cock" on the carriage return, and since it prints in both directions, the result is two images, identical, but shifted and produces a "blurry" or double-printed output.
We pulled the carriage again today, and sure enough, they were installed backwards. When the bushings are inserted in their little cavities correctly, it is a very light 'press-fit'. They will fit snugly, and will not fall out if you tilt the carriage left or right. You then secure them with the one small screw and washer for each side.
Buttoned the plotter up, and did a plot... voila!! Perfect plot without even doing a head alignment or anything!!!
It's worth a try... if you didn't remove these bushings, then I don't have any solutions for you. It's an elusive problem, but this repair sure fixed our broken plotter.
Sure beats buying a new $450 carriage assy.!!