Had to check in here tonight to provide another update--as it wouldn't be cricket if I didn't, imo! I just spent the most pleasant day & evening in many weeks watching several disks, DVD, 4k & Blu-Ray, (all scaled to 2160P) with my new Panasonic UB-420-k! I had actually forgotten what it was like to watch several hours of disk-based movies (and stream--but a ROKU Ultra does my streaming now) without a single, solitary freeze-frame/pwr off and/or Factory reset! My wife was ecstatic. Nirvana has been achieved..
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Operating on the same exact network as the x700, reliability and therefore performance is demonstrably above the x700--I was surprised, really, at the differences that were immediately noticeable on the first day.
Even the bios option UI presentation and logic is head & shoulders superior to the x700, imo--now, that's the way a bios UI should be presented! Comparatively, the x700 looks like a really almost sloppy cluster of software add-ons, extensions, and literal afterthoughts. I mean--to my eyes it is exactly as if Sony was shoehorning options willy nilly to meet bullet lists of "features" with very little pre-production planning (such as the late software support of DolbyVision, for instance, which came through a software patch after the x700 shipped.) The 420 looks and presents as if designed from a carefully thought-out master plan--the x700 simply doesn't present that way at all. (Dolby Vision isn't a concern for me--because the 420 supports HDR 10 & 10+.)
That such is the case for the x700 is fairly obvious by way of Sony's official tech support advice for power cycling and/or resetting all the options to factory to try and cure the horrific freeze-ups and lockups. I didn't see any similar "support" messages from Panasonic concerning its 4k disk players, nor was I successful in finding a copious amount of "my 4k player is freezing up constantly" for the Panasonic offerings as I found easily for the x700--page after page of complaints--and after today's freezeless marathon performance of the 420, I can see why! When you don't get freezeups, you don't write complaints about freezing up, etc...
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These are real, serious problems for which Sony has done
nothing except to offer the very lame and sufficient "power cycling and reset to factory defaults" advice & followed by "you may have to send to service if these things don't work"--that advice never worked for me permanently despite many weeks of trying everything I could think of along with following a lot of well-intentioned advice (here and elsewhere) for which I am grateful. But it wasn't enough. The x700 screams for a thorough bios update, for instance, but I could find no indication that Sony has any further plans for the x700 in that direction.
--Another thing I noticed with the x700 is that undoubtedly heat was on the minds of the design engineers as they moved the power brick out of the x700 case to the power-cord plug. The Panasonic retains the power circuitry inside the case instead of external to it because overheating of the 820/420 was very well considered and then
eliminated in the basic player design. Size of the x700 case & the UB420-k is very similar, too
__Last thing I will comment on, is I much prefer the Panasonic remote! It isn't backlit, either, but it is a good bit larger and that's great protection against hitting the wrong key accidentally, I've found. Aside from being easier and less club-fingered to handle than the Sony remote, I find the key layout far more intuitive than the Sony keys--but that impression might simply be because of the comparatively cramped nature of the x700 remote.
In closing, I have nothing against Sony--of course not. Indeed, I bought the x700 after having been so impressed with my last Sony BR player & streamer--which to my knowledge never locked up once in years of use! But something happened with the x700 on the way to market, and thus my problems have existed as I have recounted them here. As mentioned earlier, I might be more skeptical as to the origin of my x700 if it looked like the problems I've reported were rare among the x700 user base--but when I can find many Internet forum pages in which people report the same problems I've had, I really have to dismiss the idea that I purchased a cheap knock-off product
direct from Amazon (I didn't buy from a third-party AMZN retailer, etc.) No, I think the design as it sits is flawed in different ways--but not enough that 100% of production units are affected, of course...
Thanks again for the kind suggestions I received here in these forums--there wasn't a one of them that I ignored...
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Now--it's back to enjoying my movies & music, etc.! Delighted to do so!