I spent full day trying to find service locations, schematics, sources for parts, or simply answers. I finally wrote Meg Whitman at HP and got a helpful response from a service office:
1. Parts not available
2. Schematic not available
3. Problem (mine at least)clearly mechanical - gear busted.
4. No solution - no repair - at least at practical costs.
5. HP gave me a deal on new species (Envy 7640) with similar features. Half price reconditioned machine, one year warrantee, shipped free. $80.
6. More or less, service rep agrees printers by HP are not expected to by repaired.
It is the old business model of cheap razor, pricey blades (ink.) Printer is a big razor and a lot of waste and mess in trash heap - but HP doesn't give a %#*@.
I will not buy their lines anymore - printers, PC, or whatever. If anyone wants a couple of new 564 ink cartridges (HP) unopened, write me and I'll mail.