I always had a love/hate relationship with these printers. Hate them because they're a maintenance nightmare - which always starts with "How the **** do I get the outer covers off?"
until I refer the manual (here, a copy stored on-line). Love 'em because they're built like a battleship: totally over-engineered and just seem to go on and on . . . until the inevitable paper jam.
A common jam is at the top of the paper path, just before the print gets spewed out into the top tray. And it happened today - again. But the cause (so I believe) is well-known . . and perhaps the fix is . . . anyway, here's my mine.
At the top of that path the paper is pinched between plastic rollers and several soft-ish rubber rollers. (These are on a rotating shaft which is driven from the main motor). It's the latter that lose their friction. So, the paper gets fed to those rollers; the rubber rollers skate over the paper; the paper doesn't move; the paper still gets fed to those rollers and . . . paper jam. The fix is to restore the frictional surface of the rubber rollers: I use fine emery cloth, 300 grade - works every time. And, most importantly, that fix lasts - and it is cheap!
Aside.
HP may - or may not - still have the service manual available on-line from their archive. If anyone has a need for an extract from that, send me a P.M.
Al.