I have an HP6 Laserjet. It works like a charm except that the printing is now coming out with light gray vertical bars down every page. I read HP's site and they suggested running a software package to help clean it up but its not compatible with Win7. Any ideas on how to improve the print quality short of getting a new printer?
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You may need to clean the corona wire. Some laser printers have a little brush stowed inside (often included with a new toner refill).
Download the printer manual from HP to see how to do it on your model.