The dreaded print alignment page

[imc0]

I'll put a specific question at the top: where is the media sensor on the HP Officejet Pro 8000 and how do I take it off to clean it?  If it's not working, is there anywhere I can buy a second-hand or aftermarket one (or indeed an original one, though I suppose they are not made any more)?  Please read on for further details and more questions.

I've rescued an old Officejet 8000 from a cupboard.  Given the environmental concerns of today's society with re-use wherever possible it seems a shame to just bin it, as it's actually a decent printer even though it is of course no longer under support from HP.  I've procured some sealed original HP ink cartridges (dates were a bit old but you can't have everything) and spent some considerable time cleaning the print heads.  It now prints a darn-near-perfect print quality page.

But of course, every time I send a document to the printer it: prints a page with some coloured bars at the top and the rest of the sheet blank; goes to "cleaning print heads" for several minutes; prints the actual document; prints another page with the coloured bars; goes to "cleaning print heads" for many more minutes, and eventually says "alignment failed".  Every time - at least for the first dozen or so documents, and then it stops doing it, until the power is cut or the paper misfeeds and then it starts all over again.  This is a massive waste of time and of ink - I've replaced each colour cartridge twice with sealed new ones, and the yellow is now showing nearly empty for the second time, and I can only have printed a few dozen sheets, most of them black&white.

What I want from HP is:

(a) a service manual for the printer showing how to strip it down, clean it and put it back together.  There's clearly a broken or dirty sensor somewhere, and it's reasonably likely that cleaning that sensor would fix the problem.  In addition I don't know how to get the right-hand panel off from the lid of the printer.  Under there is the area where all the ink goes when the heads are cleaned, and there must be the best part of 100ml of ink in there that needs cleaning out.  With a printer this old, it clearly can't be sent back to HP for servicing, so I need enough info to be able to self-service it.

(b) if there's a hidden service menu accessible from the front panel that would let me turn the self-aligning behaviour off, how to access that menu?

(c) can we update the printer's firmware with one that has this bug fixed?  The current behaviour is clearly silly: if alignment fails (and particularly if it fails for a second time) the correct thing to do would be to show a message "alignment failed - to align the printer select [whatever] from the menu" and then stop doing it.  The printer doesn't need to be aligned - it is actually printing fine.

[imc0]

 Answering my own question... the sensor is on the right-hand side of the print-head carriage.  To access, open the lid and press OK for 5 seconds so that the print heads come out.  Shove them a bit to the right for better access.  The cable going to the sensor can be unplugged and then the sensor itself can be removed - the trick I was missing was to push in on a tab that goes down behind the sensor.

[imc0]

The tragic end to this story is I accidentally broke the lens on the sensor while trying to clean it because it looked like there was ink under it (and it does come off, it was just... more fragile than I thought).  So it pinged off in two pieces and I also found a tiny colour filter - I suspect there may have been a second one which is now lost.  Although I've reassembled it as best I can, it still doesn't successfully align.  However, the printer now does something it never did before: it prints the full alignment page (and sometimes a second one with a different pattern) instead of the one with just a few bars at the top.

So unfortunately this printer is probably destined for the bin, and all for want of a piece of plastic 2cm long and a firmware programmer who could have coded for non-pathological behaviour when the alignment sensor is broken (as it still prints fine even now when it's not chugging along trying to self-align).