I finally got around to scanning what information I have from Panasonic on these two players. I apologize in advance for the scan quality, they were sent to me from Panasonic as printed copies of low-res scans so they were pretty terrible to begin with.
The LX-1000U is known for having tracking issues and being terrible with CLV discs. Panasonic acknowledged the problem, but didn't really offer a good solution (they recommend replacing the pickup with a newer version). Here is the bulletin:
https://drive.google.com/file/d/0BzkSpoC0EjDta0FqanczQWVpVW8/view?usp=sharingThe LX-900U has an issue with APL or Average Picture Level. Nothing from Panasonic mentioned this issue, so I think they never officially acknowledged it. The Perfect Vision's review of the LX-900 mentions the issue and the response from Panasonic was that they couldn't recreate the problem and the reviewers likely had a faulty or out of spec unit. Nevertheless, MSB/Runco figured out what caused it and fixed it. Panasonic did change a number of parts in the player over time and here are the changes:
https://drive.google.com/file/d/0BzkSpoC0EjDtUDhNV2ZWSnRIZU0/view?usp=sharingAnd the original parts list:
https://drive.google.com/file/d/0BzkSpoC0EjDtdlRCTWVXcXV2T28/view?usp=sharingThe schematics for the LX-900 are hosted on LDDB. Maybe someone smarter than I am can figure it out.
Enjoy