I just replaced the bad drive in my Pioneer 810H with a 300 gig unit
from Weaknees. Their hardware instructions were flawless, and the
Pioneer unit was designed to come apart, replace the drive, and go back
together easily.
There was an issue with updating the software, though. The guided
setup goes immediately to connecting to the TiVo service, but it
doesn't update software. When the 810H powered up, it booted with
sotware version 9.1. You need at least 9.3.1 (9.3.2 is currently
available) to the recorder can control the converter. I had to force
the software update by selecting "Reset".
Other than that minor bump, the upgrade was easy.