The essential DX7 literature: THE COMPLETE DX7 by Howard Massey
Brought out by kind and helpful people of Vintagesynth.com community, trimmed and reduced in size by me. Extremely difficult to find in decent quality, now hopefully available for good through these links:
Abundance of both general Yamaha synth and the DX range links and goodies.
- Yamaha zone on Synthzone.com
- Somewhat hidden folder on Synthzone.com with pretty much everything you need for DX7
DX7 II D/FD Battery change procedure by Michael Zavoski
Something you don't want to miss, inevitably you'll need it one day!
I've tried it myself recently and it worked like a charm.