Quantcast JVC Technical document about Dynamic Drum and BEST/Video calibration - digitalFAQ Forum
Go Back    Forum > Digital Video > Video Hardware Repair

Reply
 
LinkBack Thread Tools
  #1  
05-23-2021, 09:24 AM
hodgey hodgey is online now
Free Member
 
Join Date: Dec 2017
Location: Norway
Posts: 1,266
Thanked 326 Times in 278 Posts
Some person finally put this on the web. JVC published a number techical guides over the years describing new features on their VHS lineup. This doc was referenced in the later one that covered the 1998 models (HR-Sx500 and so on) and some service manuals, but I had no luck finding it published anywhere.

This doc describes the inner workings of the dynamic drum system, specifically for the pre-1998 models, as they changed the mechanism a fair bit for that lineup (after which there were only minor modifications untill the very late-model decks like the sr-vs30u which used a substantially different mech). The 1998 guide has a whole section on the mech, but doesn't note anything about the dynamic drum system so I presume they didn't alter much of the core principles of it.

As has been subject to a bit of discussion in the past, the doc notes that it is only used for "trick play", and is not active during normal playback. It also notes how it's initialized electronically, which could maybe give some clues to how to disable it without doing to much manual tinkering, tho as mentioned they changed the mech a bit for the later models that we're mainly interested in.

The BEST/Video calibration function is also covered, the playback part seems to be a bit more simple than I thought it would be, altering some EQ parameter (not entirely clear if it's on the rf signal or the demodulated video) if the video signal frequency spectrum deviates from some pre-set default. It's not impossible that they made it more complex later though, but I don't know.

Attaching both here in case they disappear from the original location.


Attached Files
File Type: pdf JVC HR-VP830U E939EG J936MS video VTG82081.pdf (2.23 MB, 12 downloads)
File Type: pdf hr-s9500_en.pdf (1,011.6 KB, 13 downloads)
Reply With Quote
The following users thank hodgey for this useful post: sevarre (06-12-2021)
Someday, 12:01 PM
admin's Avatar
Ads / Sponsors
 
Join Date: ∞
Posts: 42
Thanks: ∞
Thanked 42 Times in 42 Posts
  #2  
05-23-2021, 03:53 PM
latreche34 latreche34 is offline
Free Member
 
Join Date: Dec 2015
Location: USA
Posts: 1,883
Thanked 314 Times in 292 Posts
Thanks for the documents, I certainly haven't seen it before, Yeah I figure that DD system is not activated during the normal playback by watching it working. I talked about it in one of the old threads here and at VH. Maybe now I can revise the "DD disable procedure" by at least using the JVC names, I was calling the parts different names.

As to the video calibration, a.k.a B.E.S.T I believe it equalizes the RF signal like any other type of magnetic recording, because what's recorded on tape is modulated RF not video signal.

I posted those documents in the procedure's thread, Thanks a lot.

Quote:
3.1 BEST SYSTEM
Best system refers to combined auto calibration during
recording and auto picture during playback. The system
eliminates the previous need for pre/rec and video circuit
adjustments when replacing the heads and reduces picture
quality degradation arising from video recording and playback
response changes due to head wear.
Oh wow, not only best has to be ON if a head replaced but it has to be ON for worn heads too, So all VCRs by now should have it ON, That's re-assuring though because now I know I can get more use of my VCR's.

Last edited by latreche34; 05-23-2021 at 04:19 PM.
Reply With Quote
  #3  
05-23-2021, 06:20 PM
latreche34 latreche34 is offline
Free Member
 
Join Date: Dec 2015
Location: USA
Posts: 1,883
Thanked 314 Times in 292 Posts
I have to admit though despite its problems the Dynamic Drum feature was one of the highest technical achievement put on a consumer VCR, Hats off to JVC for that.

This video sample shows a perfectly working DD on a pre-recorded tape, Some of the speed indicators don't show in the OSD, it's a VCR glitch.

Cannot attach sample here due to size limit.
Reply With Quote
  #4  
05-23-2021, 07:38 PM
hodgey hodgey is online now
Free Member
 
Join Date: Dec 2017
Location: Norway
Posts: 1,266
Thanked 326 Times in 278 Posts
Yeah it was a pretty interesting feature, as noted in the doc they even included pitch compensation for audio playback. Mitsubishi actually put moveable heads on their U82 SVHS model, which was a step further, but it seems to have been much more prone to failure since it needed a slip ring to control them.
Reply With Quote
Reply




Tags
dynamic drum, jvc

Similar Threads
Thread Thread Starter Forum Replies Last Post
JVC VCR Video Calibration on screen? Ruby510 Video Hardware Repair 5 05-08-2021 08:56 PM
JVC dynamic drum ultimate repair mod! latreche34 Video Hardware Repair 8 02-02-2021 02:33 PM
JVC Dynamic Drum gear remold/repair? jdogherman Video Hardware Repair 5 01-17-2021 01:47 PM
JVC Dynamic Drum system? Mejnour Capture, Record, Transfer 13 04-01-2019 12:59 PM
Video calibration message on JVC S-VHS? Jtm732 Capture, Record, Transfer 1 02-06-2018 05:12 AM

Thread Tools



 
All times are GMT -5. The time now is 04:34 PM