See Andy Hill's reply, that would be my guess too (transfer charge roller),
fairly cheap part and still available. BTW if you change it yourself be sure to
avoid contaminating the roller with oils from your fingers.
Failing that the fuser or power supply are the probable culprits and they would
be very expensive to replace (probably not worth it).
You can be sure that the problem occuring on two printers at the same time is
coincidence since the failure occurs with an internal printer test.
Tony

"JJ Jones" wrote:
We have a weird problem on 2 HP Laserjet IIP printers. If you run a
continuous print-test (Hold down Alt + Test for 5 seconds), the first
page comes out very faint. But each successive page gets darker and
darker until about the 10th page is almost perfect.

It's strange because we've had several of these printers for many years
and now 2 of them are doing the same thing.

I tested their cartridges on a good printer, and the cartridges are
fine, so the cartridge is not the problem.

Does anyone have any ideas of what the problem is? We're trying to get
some idea of the cost of repairing these things, and whether it's
worthwile.