The 6900 was not a suggested model, too old.
A JVC just cutting power is a failsafe of every JVC S-VHS deck I've seen or heard about. Something inside is direly wrong, and can be quite a few things at fault: cracked/broken gears, brittle/broken/stretched bands, etc. And there really is not a typical issue with non-9600-9911 units (where that it usually the dynamic drum gear seizing for various reasons, including being cracked, toothless, or broken).
It's very unlikely for such issues to be caused by shipping, meaning it's been bad since before you got it, therefore it's the typical case of a shady eBay
seller. This is the sort of stuff I warn others about all the time.
So, to recap:
- bad deck
- deck wasn't suggested to begin with