JVC Dynamic Drum Ultimate Fix

[hkorpim]

I have the same experience. I have called them thumb gears because they don't appear to serve any purpose, but actually the axle of these fine gears have friction fit to tape path alignment screw inside drum. For the gear on Aristarhos' foto I have one tip: Try welding it. I have welded my gears using small soldering iron with sharp tip. Press cracked parts together and close the crack by melting. I's not so easy, but possible. If you have not welded nylon before, practice it by welding zip ties (also nylon) and find suitable temperature, that melts, but does not burn the plastics. The axle fit of these gears should not slip and may require super glue.

In my DD gearbox also the worm drive started to skip gears. The spiral gears did not show visual cracks, but the axle was sitting too loose and was a bit noisy under load. The picture below illustrates how I fixed it with a wire.

[Attachment 85316 - Click to enlarge]

[Aristarhos]

I have the same experience. I have called them thumb gears because they don't appear to serve any purpose, but actually the axle of these fine gears have friction fit to tape path alignment screw inside drum. For the gear on Aristarhos' foto I have one tip: Try welding it. I have welded my gears using small soldering iron with sharp tip. Press cracked parts together and close the crack by melting. I's not so easy, but possible. If you have not welded nylon before, practice it by welding zip ties (also nylon) and find suitable temperature, that melts, but does not burn the plastics. The axle fit of these gears should not slip and may require super glue.

In my DD gearbox also the worm drive started to skip gears. The spiral gears did not show visual cracks, but the axle was sitting too loose and was a bit noisy under load. The picture below illustrates how I fixed it with a wire.

[Attachment 85316 - Click to enlarge]

Thank you for your tip on welding the plastic gear. I haven't tried it because i haven't practiced on other nylon parts to find the right temperature. It is a one shot fix and if it goes wrong you end up with gears burned beyond repair. On YouTube there is a French guy who claims he had fixed the split gears with a soldering gun.
Here is his video.
https://youtu.be/zcajJJoUOk4
Unfortunately he didn't record the repair of the plastic gears, i don't speak french and the auto translation is bad. Also English is not my native language so bear with me.
This French guy also read this thread. Someone asked him how he fixed it and he replied he used a soldering iron.

[hkorpim]

I have uploaded new instruction video re disabling Dynamic Drum system. At the moment it is available through this link only, but will be public end of this week:

https://youtu.be/VaJ18J-bpzM


Youtube link updated to new version of video 14th Feb 2025.

[Aristarhos]

Thank you for taking the time to make such a detailed video.

Just a remark. Using pliers to remove the flat cable from the head drum is dangerous. One wrong move and it will tear. I've had it happen to me, that's why I'm pointing it out. I don't know if there is a safer way to remove it without excessive pull upwards.

[hkorpim]

Excellent point, Aristarhos! I should have made a note on this. I have put plastic cover on the round tips of my pliers made of heat-shrink tubing. A thin rubber tube would be even better. Anyway it must be soft against ribbon cable and with sufficent friction. I considered this method safer, than using fingers.

[lordsmurf]

For working on VCRs, I have various spudger-type tool kits, including plastic precision tweezers of various sizes. You can buy these cheap from Amazon (or probably Temu, etc).

Thanks for pointing that out, Aristarhos.

On one of his prior videos, I pointed out the dangers of adding foam (essentially heat insulation!) to the inside of the VCR.

hkorpim, please be very careful with your advice. I think you need some feedback on your methods before you post more videos on this. The VCRs are already not working, and many of us don't wish to break it more (or worse, buying your mod = so spending more money + breaking it more!)

We say this to help you, not "dump on you" as some people seem to think.

I want to see gear fixed, not ruined more. Nor do I want to see people get their tapes damaged. That's where I'm coming from.

[hkorpim]

Thank you, lordsmurf, for your valuable feedback! The reason I did not make the video public yet, was to get the feedback from this forum first. I will modify the video with a note regarding to pliers. I also have a video in preparation how I managed to get the VCR back to alingment after crack/split of the 2 gears. I will also link that video on this forum first for comments, before making it public.

[dellsam34]

The safe way to pull the head ribbon cable is to use both hands, One pulls up the plier, the other pushes down to balance the action while keeping the VCR down by both arms, this makes a more controllable and smooth pull and avoids a wrong move or one hand over shooting. This is probably just me talking mechanical engineering but such a technique is used in almost every aspect of our lives where balancing is needed, from walking on a rope with two weights on each side for better balance, to spring loaded gears and clutch discs to avoid harsh knock, wieights balancing used on elevators for smooth and less effort motor operation ... just to name few.

[hkorpim]

You are absolutely right, dellsam34! It's not so apparent, but in the video I hold left hand finger against overshooting. I'ts so tight space, that I was scared of pulling with fingers.

Have you already received the package I sent to you?

PS. My background is also mechanical engineering. Electronics and programming just a hobby...

[dellsam34]

I havn't received the package yet, I'll let you know when I do.

I wish I got into electronics and programming little earlier to learn it easier, that would have completed my knowledge for any project, Too late now, things don't sink in that easy after 50.

[hkorpim]

I have just uploaded new instruction video regarding to alignment of self misaligned VCR after DD gears have cracked/splitted. I think this can have general interest now that it is possible to operate the VCR without DD gearbox. I got my own VCR back to alignment and from that reverse engineered instructions how it was done. The video does not cover setting DD gearbox back to alignment, just the VCR. In order to utilize the method, cracked/splitted gears must be repaired to such extent, that the gears are fixed to their axles, which enable the adjustment of drum tape path (guide ring).

All feedback and comments welcome. The video is not yet public in youtube. I plan to make it public on Friday evening European time after possible feedback or corrections have been implemented.

EDIT 14th Feb 2025:

My 2 latest videos (PART 2. & PART 3.) are now public and I have made updates on them based on comments received from you. Thus the youtube link has changed. The video linked to this message has been updated with better text instructions, better fotos at the end of video and correction of typo errors.

https://youtu.be/w7tVzDlCa9w

Unfortunately due to new link youtube handles it as new video and the existing comment stay with the old version, that I now removed. I have however attached the comment and my reply here:


[Attachment 85476 - Click to enlarge]

[Aristarhos]

Hkorpim, thank you for all your time and effort.
Edit
Have a look. Your system made it to famous YouTube channel video99 co.uk!
https://youtu.be/JQTGUDFI8HI

[dellsam34]

I received my DD emulator last night, I will post my findings in the weekend. One suggestion on packing, Try to use a smaller envelope with more bubble wrap for a tight fit especially when shipping international, Having the board too loose in a bigger envelope with less padding may lead to a disaster, Shipping carriers are not kind to packages, they just don't care.

[hkorpim]

Great! I look forward to receive your experience and feedback from testing it.
The padded envelope I used was smallest available at local post office, but I take the note, that more bubble wrap should be used additionally.
I hope anyway, that the device arrived without damage. Let me know, dellsam34, if any problems or damages on the device.

[dellsam34]

I was set to install the DD emulator today (let's call it DDE from now on) on my second deck that has the DD previously mechanically disabled and though I would test it first before I do anything, Upon power up, it shut down after few seconds, I though, well, what a surprise, this is a perfect timing to install the DD emulator thinking maybe the cracks have gone beyond just the two gears, So removed the head installed the DDE, powered up, the DDE did the light sequence as it suppose to, and VCR shutts dows after few seconds, weeeow, weeeow, weeeeeeeow. I was not up for a big repair job, but since everything is apart I had to dig deeper, Started with CP resistors first, the second one I checked found blown, This must have happened the last time I used it which is about a year ago.

I'm putting an order for a CP and go from there, I was relieved but not too optimistic though, this things are getting old and everytime you touch them something breaks down. I have also started to hunt down ribbon cables for these, everytime one is removed and insrted there is a risk of breaking it, The hard plastic plate just came off of the drum motor, I've already solederd the other end directly to the stator PCB last time I worked on it. Anyone finds a source of ribbon cables manufacturers please post it. Will post back.

[Aristarhos]

You can find ribbon cables or Flat Flexible Cables in Aliexpress

https://www.aliexpress.com/w/wholesale-ribbon-cables-fpc-ffc.html

[hkorpim]

Pity, that you were not able to start testing DDE due to other issues, dellsam34. I hope you will get the faults sorted out. I have one tip for ribbon cables: Aliexpress; they have several vendors offering cheap ribbon cables with various number of contacts, pitch and lengths.

Just noted, that Aristarhos had the same tip.
[Attachment 85532 - Click to enlarge]

[dellsam34]

I will look into Aliexpress link as soon as I get my digital caliper working again to measure the pin pitch, It has a dead coin cell battery, It's always something.

[dellsam34]

While I'm at it I'm replacing all ribon cables except for the front connectors which I don't need and the AC head which was previously replaced, I will put information here for the JVC HR-S7600AM which should be compatible with most VCRs of the same family:

The ribbon cables type is called FFC FPC
Pitch is 1.25mm, connector width is 0.8mm but they don't seem to mention this, maybe the track spacing is standard.

- Jog shuttle wheel: 14pin, 14cm long like this.

- Video Head Motor: 5pin, 18cm long, Not sure if this is reversed or straight since I no longer have the connector on the stator PCB, I'm getting this connector and going with a reversed cable like this.

- TBC to YC board bridge cable: 7pin, 8cm long, this is hard to find in this configuration so I will get any pin and trim it down to 7pin, like this.

[Aristarhos]

In Europe JVC released this model as HR-S7600EU and it does not have a dynamic drum. I have two devices of this model.

[dellsam34]

If you can pop the cover and take some pictures that would help tracking down some candidate heads to replace the DD heads now that we have a way to disable the electronics, I believe this head LP20617-006A JVC DRUM SUB ASSY with 2SP, 2LP, 2HiFi and FE heads should replace high end models with the DD system.

[Aristarhos]

I will post some pictures as soon as i can.
The chassi plates of the two drums seem to have the same size and the three srew holes of the base seem to be in the same place.
But i suspect that the height is differnet because the drum with the DD system has an intermediate plate with the spring loaded srews.
So if a swap is possible, probably it will need serious tape path alignment to the input and output posts and the head that reads the pulses to find the posistion of the video. The last pisture is from a JVC HR-S7600U.
1st Photo: LP20617-001A JVC DRUM SUB ASSY 483569127311
2nd Photo: Dynamic Drum
3rd photo: JVC HR-S7600U

EDIT:
Here is a video showing the inside of a european JVC HR-S7600 without dynamic drum
https://www.youtube.com/watch?v=s1YJYaLuWRM

[dellsam34]

As far as I know both DD and non DD use the same chassis, So the height has to be the same, The only way to tell for sure is to measure both heads.

[Aristarhos]

According to the service manuals of HR-S7600U and HR-S7600EU, these are the part numbers of lower and upper drum assy.

JVC MODEL	REF No.	PART No.	PART NAME DESCRIPTION

HR-S7600U	505	LP20319-007A	DRUM SUB ASSY
	        505A	LP20030-016A	UPPER DRUM ASSY

HR-S7600EU	505	LP20617-011A	DRUM SUB ASSY
	        505A	LP20616-005A	UPPER DRUM ASSY

HR-S7611EU must be the black color model of the silver HR-S7600EU.

[lordsmurf]

In terms of PAL 7x00 VCRs, I believe a differing factor is the ability to play MESECAM, as well as language options. Not all of them can do all of it. Not including obvious external color differences.

I'm fairly certain none of the PAL 76xx/77xx decks have DD. The model numbers between PAL and NTSC don't translate 1:1. Sometimes yes, mostly not.

What I'm more curious about is the fail rate per unit.

I think the NTSC 9600,9800,9900 decks fail most, with most now existing in a failed state (or junked over the decades).
The 7600 less so.
The one you rarely hear about is the 9500.
I hope I'm not jinxing myself here, but I've never see a failed DD 9500. About 50/50 in the 7600. And at least 90% of the 9600-9900.

FYI, I mostly think of the 9500 not having room in the deck, no space like the others. I believe some of the PAL DDs are equally space-less. In those cases, there's no even room for zip ties, nothing to tie too. Hence 3D printing. But if it can be seated under the transport now, that is a moot point.

[lollo]

I think the NTSC 9600,9800,9900 decks fail most, with most now existing in a failed state (or junked over the decades).
The 7600 less so.
The one you rarely hear about is the 9500.
I hope I'm not jinxing myself here, but I've never see a failed DD 9500. About 50/50 in the 7600. And at least 90% of the 9600-9900.

I have used intensively the DD in my HR-S9500MS and never failed. I stopped some time ago to avoid problems, but this is (just) an element fot your theory.

On my 9600 and 9800 I always tried to do not use DD, aware of the potential issues, so no data here.

[Aristarhos]

In terms of PAL 7x00 VCRs, I believe a differing factor is the ability to play MESECAM, as well as language options. Not all of them can do all of it. Not including obvious external color differences.

I'm fairly certain none of the PAL 76xx/77xx decks have DD. The model numbers between PAL and NTSC don't translate 1:1. Sometimes yes, mostly not.

What I'm more curious about is the fail rate per unit.

I think the NTSC 9600,9800,9900 decks fail most, with most now existing in a failed state (or junked over the decades).
The 7600 less so.
The one you rarely hear about is the 9500.
I hope I'm not jinxing myself here, but I've never see a failed DD 9500. About 50/50 in the 7600. And at least 90% of the 9600-9900.

FYI, I mostly think of the 9500 not having room in the deck, no space like the others. I believe some of the PAL DDs are equally space-less. In those cases, there's no even room for zip ties, nothing to tie too. Hence 3D printing. But if it can be seated under the transport now, that is a moot point.

I had three 9500s and the two have failed. The one that failed was repaired and sold.
Maybe a factor is the variation of the temperature in the place of storage. The plastic expands and shrinks between hot and cold temperatures and that maybe deteriorates the gears.

[dellsam34]

According to the service manuals of HR-S7600U and HR-S7600EU, these are the part numbers of lower and upper drum assy.

JVC MODEL	REF No.	PART No.	PART NAME DESCRIPTION

HR-S7600U	505	LP20319-007A	DRUM SUB ASSY
	        505A	LP20030-016A	UPPER DRUM ASSY

HR-S7600EU	505	LP20617-011A	DRUM SUB ASSY
	        505A	LP20616-005A	UPPER DRUM ASSY

HR-S7611EU must be the black color model of the silver HR-S7600EU.

Part #s don't tell the whole story, You can have two identical heads with one has a FE head and the other not and the part # would change to something else, We have to figure this out by experimenting and sharing pictures, There is a good supply of brand new heads out there that we can use up to keep the VCRs going for many years to come.

[aramkolt]

I'm still pretty sure any video head in any of the more common 3600, 3800, 4800 JVC S-VHS VCRs can be used in place of the original DD decks. In fact, you can just swap over the entire deck in most cases. The ones that don't have flying erase heads make the connection easier, but the ones that don't just need the ribbon aligned all the way to the pin 1 side. The last two pins that are missing are where the flying erase pins are. The VCR will play without the head data pins plugged in at all, so not having just the flying erase head connected isn't going to stop it from working at least in terms of playback.

I've recently built an extension cable to move the disabled DD unit off to the side of the VHS deck so that the appropriate signals still go to the main board as you do still need something to send signals to the main board to keep it from shutting down.

I would have already tested this, but I don't currently have a DD deck with worn heads that need replacing to make it worth doing. It is possible that some heads have slightly different characteristics such as hardness or possibly frequency response, but in some cases, the drums used are identical across models - like the 4800 and 7800 (though both non-DD decks) do have identical part numbers in the service manuals. I wouldn't be surprised if the 7800/9800 are also the same upper drum part number. I have done a direct swap of a 9600 drum into a 9800 VCR and by the part numbering system, those were made/released 2 years apart, so again, I think most upper drums are physically compatible. Some might wear out sooner than others if they are made of softer materials, but hours of use are likely to be less in general of the lower end units that no one has really been searching for specifically since they lack line TBCs.

[dellsam34]

Swapping out the entire deck is also a good idea, One thing to not about the drum motor is that there are variations of NTSC, PAL and Multi-System, I've seen at least 4 and 5 pins ribbon cables depends on the speeds available for different standards, So the rotor magnet, the stator PCB, the ribbon cable have to be married to the main board of the VCR, The deck and the head assembly can be swapped with equivalent family. For DD VCRs the entire drum assembly has to be replaced, swapping the upper drum will not get rid of the DD problems, plus replacing the upper drum only will require tape path alignement.

The low end models have a different head setup, Usually the family with a belt driven DD system, the non DD heads look like this.