Ive got hold of a pair of machines. One is a playback only, and this one is the recorder.
They come with a separate controller-panel for 'syncing up' the two for editing.
At the moment, I'm having fun with the recorder. When I got it, the cassette lift was out of sync and jammed. I sorted that to find the pinch-roller jammed by solidified grease. I cleaned all that lot and guessed the timing by comparing with the play only machine--which mechanically appears to function.
It was doing some weird stuff, lacing/unlacing and switching off, showing various error codes, this has been helped--but not totally cured by cleaning the mode-switch and resoldering loads of dry-joints in the PSU.
Currently, I cannot get the thing to record in 'Hi-Fi' sound. The Hi-Fi beacon on record is not lit, although the level meters indicate audio into the recorder. It however, Plays Hi-Fi from a pre-recorded tape quite normally, beacon lit and excellent sound, no flutter or other nasties.
Currently, its not connected to the control-unit, and the remote/local switch set to local--so all the functions appear to work.
Another oddity is that it will not record in 'S-VHS'....
--- Ive botched a tape to make the machine think its got an S-VHS tape, (Hole in the channel near the right-hand edge) which when inserted the S-VHS beacon is lit,--but on selecting 'Rec' it goes out and records in normal VHS--Playback picture--For VHS is however pretty excellent.
All the 'rock-and-roll' functions work very smoothly, hard to think its actually a Tape and not some other media..
I'm not completely sure that I have the deck-timing correct, although it appears to function/lace/unlace etc fine, and cant find a service-manual for this huge and very complicated machine....
Any ideas....?
I had a look through my JVC manuals and CD indexes, there appear to be three similar models listed with different suffixes from 1994 to 1996 but the 'E' version is listed at 1994.
They are, or were available on CD-rom, JVC part number SML0016, which unfortunately I don't have. 
However if they use a normal JVC deck from that era then I may well have the timing diagrams from a different manual. 
A picture of the deck, upper and lower side would help a lot, as the model number does not ring any bells with me.
Ahh--Thanks Red...
Since posting, Ive managed to locate a manual for the S800U machine....
My partner asked why I don't I try another different search-engine instead of google--
'Dogpile' led me to a Forum and a link to an American guy's site that had the whole manual and instructions for use...
It appears there's various settings that can be accessed via the counter-display and on-screen menu that allows setting up for sound and recordings--One setting turns HiFi on or off.... 
Bit late tonight--so I'll have a fiddle tomorrow eve....
Altering the various settings in the menu that JVC call--'switches' has restored full operation.
Machine works normally--even recording S-VHS on a modded VHS cassette with a higher quality than std. VHS.
--Research suggests that recordings made this way will not last long--degrading quickly over time due to the incorrect coercivity of the tape for the S-VHS system....
Not sure if its normal--but the 'video PWB' gets extremely hot! There's a million of those 'orrible S.M. electrolytics on that board, and at a guess--these are running at around 60-70 deg. C! Main area is in the vicinity of the LPF stages and a chain of DC coupled video amp stages....
Going to check the supplies next--just in case!
High bandwidth analogue amplifiers do get warm.
Is the set supposed to have a fan in it?
There are bits of kit out there that require the covers on for the fans to be effective.
I have seen pro gear with fan sensors on it in the past.
You would only be warned about this in the full service manual.
Well--Guess you're right! All supplies are spot-on.
There's no fan and no provision for one....
--The heat is coming from the surface-mount transistors on the left-hand side of the 'Video-board --Of which there are loads! The two chips,--Sony devices get fairly hot too.
Ive aquired some low-profile heatsinks and some 'stuff'....
This stuff is odd. It came from a Samsung plasma--between the Y-SUS board and the main chassis. Its like Plasticine, a putty like sheet made for heat transfer--Weird stuff, Its very 'cold' to the touch and has a silicone feel to it, and is non-conductive--Ive seen it used on T-Con boards covering the chips etc....
I plan to mount the heatsinks on the hot area and 'stick' them with this 'stuff', maybe add a little fan in the chassis
Ive checked the deck alignment--and its a wonder it was working at all! All corrected and both player and recorder working great--Best VHS recordings Ive ever seen.
It goes to show just how Good VHS Can/Could have been--and thats rec/play in Std. VHS. Must get a Proper S-VHS cassette now to see how good that is......
Ive aquired some low-profile heatsinks and some 'stuff'....
This stuff is odd. It came from a Samsung plasma--between the Y-SUS board and the main chassis. Its like Plasticine, a putty like sheet made for heat transfer--Weird stuff, Its very 'cold' to the touch and has a silicone feel to it, and is non-conductive--Ive seen it used on T-Con boards covering the chips etc....
...
Aah!, good old "dead toad". 
Dead-Toad! 
Sounds like you're well familiar with this stuff! That is nearly a perfect description of it--Sorta clammy and dead cold.......
What is it actually called--Any info for it?
Hi Alastair, I've got half a dozen Panasonic editing machines two of which I bought from trevor (murphyv310) which still work ok. but the newer AG7700/7800 are rather poor performance wise (probably knackered) and I cant fathom the set up procedures either. but it's good to hear your machines are running well.
Cheers,Neil.
Hi Neil,--How you doing?
I think I got very lucky with these two--The recorder only has 660 hours on it and the PB machine has 1200 odd--Looking at the machines generally, wear wise and condition--this looks feasible as being an accurate time of use.....
The setting procedure (for the JVC) is done by the 'tape-counter' and on-screen display, selecting say, 200 for the first two digits and either 0 or 1 on the last digit for the hi-fi sound on or off...
Everything (mostly!) is settable like this, either in the user menus or the service menus. Even tape backtension is set by the 'software' and tape-counter in a similar way to the above....
--The Pans are probably much the same idea, you just need that all important user/service-manual for 'em....
Maybe they are 'stuck' in S-VHS and are recording in S-VHS--giving poor results on std. tapes....
