Repairing the HP LaserJet 4 Laser Printer
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I've now carried out this repair on three HP LaserJet 4 (and 4 Plus)
printers, and it seems to be a common failure as well as a straightforward fix.
First of all, the symptoms of the fault: the printer prints the page
as normal, but then the paper jams up as it exits from the printer,
usually ending up partly sticking out of the exit rollers.
When removed from the printer, the page is OK at the top of the
sheet, but crumpled at the bottom.
If you grab the leading edge of the paper as it begins to exit, and pull,
it will feed out normally.
The Rollers
Look closely at the photo above (click for a bigger version);
note the difference between the left-hand roller and the right-hand one.
The rubber roller on the left is shiny and slippery, which is sometimes
referred to as a “glazed” appearance.
The right-hand roller is matt and has a much more “grippy”
surface (it has a higher coefficient of friction).
The shiny roller is the cause of the trouble, and has become glazed
through many hours of feeding hot sheets of paper out of the printer's
fuser.
To rememdy the problem, I've cleaned the rollers with the “petrol”
that is sold for use in cigarette lighters.
It's not actually the same petrol (gasoline) that one puts in a car,
but a petroleum spirit called
naptha.
Similar naptha fluid is also sold for use in camping stoves.
The lighter fuel attacks the rubber of the roller very slightly
(don't leave the fluid in contact with the rubber for too long) and
roughens the surface.
This slight roughening restores the frictional properties of the
roller, and makes it feed the paper properly again.
