Quantcast JVC Dynamic Drum system? - digitalFAQ Forum
  #1  
02-06-2012, 04:16 PM
Mejnour Mejnour is offline
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I would like to know if it's just a "fancy" feature to look "without the noise" the picture when you forwarding or rewarding at high speed?

Quote:
TimeScan with Dynamic Drum System
The unique TimeScan function uses JVC's original Dynamic Drum System which precisely tilts the head drum to match the tape velocity, delivering noiseless fast-motion playback in forward and reverse at speeds pf up to 9 times normal. So you can catch the day's news or breeze through long sporting events and other recorded programmes, in just a fraction of the time you'd spend otherwise. But there's more to TimeScan than a distortionless fast-motion picture - a Digital Audio Memory actually plays back the sound in the proper direction and at normal speed, even when scanning in reverse!(TimeScan audio is monaural. Sound loss may be noticeable particularly during higher speeds) So you can search for what you want based on what you hear as well as what you see. TimeScan from JVC - advanced technology for advance viewing.
Also a preservationist who seem to like this feature

Quote:
I should also mention that the Dynamic Drum System that many JVC VCRs have (7600, 9500, 9600, etc.) allow them to playback almost any tape. This system dynamically tilts the scanner to optimize the tracking in a way that other VCRs can't. I have read your original LINK, and given the range of tape qualities you mention, this feature may be valuable to you.

I have accumulated many JVC VCRs over the years, so I have the luxury (or the curse) of selecting the "right" one for each tape. But I must say that if I was only allowed one VCR, it would be my HR-S7600U because of the TBC/DNR option and because of the Dynamic Drum System.
And finally I guy (lovelogics) who says he did some modification for the DDS

I guess the right way to see if there is a difference would be to compare the HR-S7800S vs HR-S9800S!?

And you what do you think about it?

I ask because if this feature can give me a + I will not hesitate to get a deck with this system!
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  #2  
02-06-2012, 06:43 PM
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That quote is from davideck -- I should also mention that the Dynamic Drum System that many JVC VCRs have (7600, 9500, 9600, etc.) allow them to playback almost any tape -- somebody I respect, but don't always agree with. We have conflicting ideas sometimes on what certain features can do, should do, and do do. He leans towards theory and dictionary definitions, while I heavily defer to observation and experiment.

Because of my decade of praising JVC VCRs online, I've often been accused of being a JVC stock holder, shill, etc -- all silly accusations -- but I keep myself grounded firmly in reality when it comes to praising JVC hardware. And the reality is that JVC with-TBC S-VHS decks play most tapes beautifully, and a minority of tapes terribly -- Dynamic Drum or no Dynamic Drum. I've yet to observe a marked difference in how the units handle VHS tapes. The build quality of decks tends to matter more than the presence of the drum.

While I don't doubt the theory of the Dynamic Drum, I've just not observed a massive difference in performance in the past 15 years. (I realize this may counter some of my past posts online, where I have suggested it's an important feature to have. Some would call it flip-flopping, but I call it updating my belief after a further review of evidence.)

I think the transport systems matters more, along with the wide heads, in terms of playing back EP/SLP tapes. The different transport found on the AG-1980 is the main reason that VCR is so good at longer-play tapes. But it has it's own issues with magnetic dropouts and jittering sometimes not found in the JVC decks.

The 7800-7900-SRV10-SRV101 are essentially the same units, from what I've read and seen.

There's no perfect VCR.

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  #3  
03-14-2019, 08:18 PM
latreche34 latreche34 is offline
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Finally my VCR's Dynamic Drum System has failed, The rewind is partially working due to the DD gears get stuck.

I opened it today did a full clean and lubrication of the entire tape mechanism and I noticed one of the black gear is split,Time to hunt for a donor deck. Does any one know what models have DD besides the S9800, S9700, S9600 and S7600 ?
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  #4  
03-14-2019, 08:41 PM
hodgey hodgey is online now
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The S8500, S8600, S9400 and S9500 do as well it looks like, may be more S-VHS decks that had it too, including some of the professional broadcast ones (which are probably not compatible, and quite expensive).
EDIT: Also the S9900 and the S7500U (US) but not the E* one, seems the 8xxx naming wasn't used for US decks?

There are also some standard VHS decks that had it, with the naming JVC HR-DD### which may be cheaper.

It ma be safest to find one from the same year/lineup, the the lower and higher end models seemed to share a fair number of parts and pcbs (Or at least for the *500 series). Don't know if they changed the parts between releases.
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  #5  
03-14-2019, 08:48 PM
latreche34 latreche34 is offline
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Thanks man, The search is on. I just hope that the consumer models have the same system.
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  #6  
03-14-2019, 09:46 PM
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Like Panasonic caps, all JVC DD gears are now failing en masse. Mine included.

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  #7  
03-14-2019, 10:11 PM
latreche34 latreche34 is offline
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I took one gear of each side to disable the DD sensing, Most tapes played fine but I have few home recorded tapes that worked before and now are slightly miss tracking, So DD system does help playing back a wide variety of tapes.

I wonder if there is an adjustment procedure when installing the gears back, There is no mention about it at all in the service manual, Kind of spooky.
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  #8  
03-14-2019, 10:41 PM
latreche34 latreche34 is offline
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I just bought a JVC HR-DD840U I hope the dynamic drum gears are identical so I can swap them out if not it was only $36 including shipping, Someone has to make a jump and let the members know.
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  #9  
03-15-2019, 04:45 AM
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Quote:
Originally Posted by latreche34 View Post
Someone has to make a jump and let the members know.
Indeed. Thank you.

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  #10  
03-15-2019, 07:26 AM
NJRoadfan NJRoadfan is offline
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I have both the HR-S7800U (purchased in 2000*) and a HR-S7500U, the latter has the dynamic drum. The 7500 has no problems playing back EP tapes or tapes with Hi-Fi audio tracks, while the 7800 always had problems since new. I don't attribute it to the dynamic drum feature though, EP and tracking were always JVC weak points. According to JVC's own literature from the 1990s, the DD system was to allow for noise free "trick play" functions like slow speed reverse and fast forward, along with snow free freeze frame. During normal playback, it works like any other VCR.

*Back in late 2000, I originally purchased a HR-S7600U, an older model that DID have the dynamic drum. The vendor sold me the "upgraded" 7800U in its place instead. In reality it was a downgrade because the 7800U was a fancy 5800U with DigiPure vs. the 7600U being a stripped down 9600U. In hindsight, it was apparently a good thing since the DD breaks! I suspect JVC knew the DD mechanism was a problem area and eliminated it from all the DVHS decks. Cheaper memory made digital freeze frame a reality without fancy mechanics.

Popular Mechanics had a piece about the system with diagram back in 1995 (ironically DVHS decks never got it): https://books.google.com/books?id=_2...rum%22&f=false
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  #11  
03-15-2019, 11:03 AM
latreche34 latreche34 is offline
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Thanks for book link, Now at least we have an idea on how this could possibly be realigned:



Attached Images
File Type: jpg JVC Dynamic Drum System.jpg (59.0 KB, 89 downloads)
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  #12  
03-19-2019, 09:59 PM
latreche34 latreche34 is offline
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Well I got the JVC HR-DD840U today aaaaand no, It has a different DD system, even gears are different is size and teeth, Here is how the HR-DD840U DD mechanism looks like:






And here is how the HR-S7600 DD mechanism looks like:



Attached Images
File Type: jpg IMG_3286.jpg (81.4 KB, 176 downloads)
File Type: jpg IMG_3287.jpg (71.3 KB, 76 downloads)
File Type: jpg IMG_3281.jpg (94.1 KB, 180 downloads)
File Type: jpg IMG_3282.jpg (59.9 KB, 76 downloads)
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  #13  
03-29-2019, 02:37 PM
latreche34 latreche34 is offline
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It turns out JVC used two dynamic drum systems for VHS and S-VHS decks, So S-VHS decks can only take parts from another S-VHS deck, Here is a list of most US S-VHS models with and without DD drum:
http://www.us.jvc.com/archive/video/supervhsvcrs/

I'm experimenting a new way of replacing the entire mechanism from a DD S-VHS VCR and replacing it with one from a non DD S-VHS VCR, So far after reading a lot of service manuals I found out that all S-VHS VCR's that share the same mechanism design use the exact same drum, 7 heads (2 SP, 2LP, 2HiFi, 1 flying erase, 13 pin ribbon cable), So it don't matter if the VCR is PAL, SECAM or NTSC, All signals are handled by the VCR circuit boards.

But there are 2 types of stator boards, 4pin and 5pin (for different speeds), I think there is a solution for this, You can keep the the original stator board as long as you keep the magnetic rotor with it (same pole number) and put it on the donor's mechanism head assembly, I believe removing and replacing stator/rotor without removing the upper drum will not screw the alignment.

After putting a new mechanism I will see if I can put a resistor to mimic the DD tiny motor instead of keeping there spinning for no reason.

Last edited by latreche34; 03-29-2019 at 02:56 PM.
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  #14  
04-01-2019, 07:49 AM
NJRoadfan NJRoadfan is offline
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The older design looks more robust, but has a belt. The later design looks to be direct drive (unless the belt is hidden), but multiple levels of plastic fail. They shouldn't have skimped on the plastic around the pivot point of those two gears being driven by the worm gears on the bottom.
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  #15  
04-01-2019, 12:59 PM
latreche34 latreche34 is offline
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Quote:
Originally Posted by NJRoadfan View Post
The older design looks more robust, but has a belt. The later design looks to be direct drive (unless the belt is hidden), but multiple levels of plastic fail. They shouldn't have skimped on the plastic around the pivot point of those two gears being driven by the worm gears on the bottom.
I haven't seen motorized hubs on JVC models at least up until the 90's models, I have the latest D-VHS model from late 90's and it doesn't have motorized hubs, I don't know what you're referring to.

Unless you're talking about dynamic drum mechanism which I think it has nothing to do with older or newer, VHS decks used belt driven and worm gear system, S-VHS used worm gears only for the DD system.
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  #16  
06-07-2019, 10:46 PM
latreche34 latreche34 is offline
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Quote:
Originally Posted by latreche34 View Post
I took one gear of each side to disable the DD sensing, Most tapes played fine but I have few home recorded tapes that worked before and now are slightly miss tracking, So DD system does help playing back a wide variety of tapes.

I wonder if there is an adjustment procedure when installing the gears back, There is no mention about it at all in the service manual, Kind of spooky.
Let me correct myself here, No DD system DOES NOT help the normal playback or recording, It is only for forward search, reverse search, pause, reverse playback, frame by frame forward and reverse:

Details here on how to disable the thing.
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