Well here's the bad news and the maybe-not-too-bad news...
I've been an XLH1 user since the cameras first came out, and we recently experienced a similar problem.
Based on my experience (and the solution we finally had to come up with), the bad news is that I'm betting that your tapes were recorded that way... and that's the way the footage now is and there's not too much you can do about it.
The poor playback in the viewfinder obviously lets you know it's not a capturing or edit system problem, and the fact that it won't play in your HV20 is a strong sign that there was just a recording problem during the original shoot.
I won't say this with absolute 100% authority, but I think it's very likely that your footage is what it is, and can't be recovered any better than it already is.
We drove our H1 two hours to the camera tech guy that we use for repairs. He worked on it (and cleaned it within an inch of its life) for a couple of hours and ran all the diagnostics on it and couldn't exactly figure out the problem. He could clearly see on his scopes that it wasn't recording a good signal, but couldn't pinpoint exactly why. He thought maybe the heads had gone bad, maybe it was an alignment or transport issue, he just wasn't sure.
On his recommendation we overnighted the body to a more specialized camera repair place in California who said the easiest/fastest/cheapest way to do it would be to put a new "kit" in it... which is basically all the mechanical and transport parts. So we got new heads, rollers, transport mechanisms, and all that jazz. It works great now... and part of the good news is that
mechanically (although not electronically) we basically have a brand-new camera now. The also-not-terrible news is that it wasn't back-breakingly expensive... only about a $600 repair (and they did it in one day and overnighted it back to me). Not too bad for what was originally an almost-$10K camera.
Wish I had better news about the existing footage, though. I could be wrong (and hope I am), but I don't think so....
T2
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Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com