I have a 4M that's over 15 years old; I hope it keeps working forever.
Wonderful product.

I had a similar problem several months ago with the sudden apparance of wide
horizontal black stripes across the page. You could see the text or graphics
"behind" them.

I assumed there was something wrong with the printer itself. * After some
slightly acrimonious arguing with an expert on the HP user site, I schlepped
the printer to a printer service shop who was kind enough to make a test
print with their cartridge.

No problems. There was nothing wrong with the printer.

I bought a new HP cartridge, and it's worked fine since.

I'm have a lot of experience service electronic equipment, but the 4M is not
a product I'd like to rip into. I'd recommend finding someone with a spare
cartridge to confirm just where the problem lies.

If it turns out the printer needs repair, you find it much less expensive
to buy a used, (supposedly) reconditioned one. They're all over the Web, for
cheap.

* Part of the reason was my assumption that the laser discharged the "white"
areas on the drum. Actually, it discharges the "black" parts of the image.