JVC Dynamic Drum Ultimate Fix

[dellsam34]

2) The space under drum is very limited even if DD gearbox is removed, because the drum leans left and almost touches DD emulator.

3) Plastic part in the picture below slides in direction of red arrow and touches DD emulator slightly.

I see a lot of unused space in the PCB, You can redesign it to make it shorter so it will fit within the DD cavity.

[themaster1]

Trying this DD mod (i don't have the emulator) so i guess i'll try 2 options: resolder the gears or just disable DD.

Anyway, i can't figure out how to remove the 4 gears for now if someone did it before, let me know the procedure, don't want to break things. THANKS

[dellsam34]

You unscrew them just like screws.

[TOM11]

Thank guys for answers...

Maybe a stupid question, but...
Isn't it a good idea to adjust the alignment of the drum relative to the tape after removing it and reassembling/returning it to its original location?

[themaster1]

You unscrew them just like screws.

'K i'll try that

In the mean time i tried to resolder, not sucessful though, but the black gear on the left miss at least one tooth, that's not helping.

[themaster1]

Ok sucess for these (i put back the two big) , then there are the 2 screws with a spring, should i 3/4 turn these or not really ? (back to neutral position doing so, as i understand)

[themaster1]

It's a wrap ! I did a 1/4 turn for the 2 screws. I did have to tweak the P2 guide after that (snow on top) , nothing i'm not accustomed to. Then again, i don't know the history of this deck, best 10 bucks spent recently.

[hkorpim]

Removal of gears explained on my video:
https://youtu.be/w7tVzDlCa9w

IMPORTANT: Do not unscrew lead ring alignment gears! It will misalign tape path. These two gears must be pulled off without rotating them.
If you remove the gears for repair, you must place them back in exactly same position as they were. Otherwise DD no longer works properly and there will be noise bars on screen. Only try the alignment, if it is lost due to gear cracking /skipping teeth.

[hkorpim]

Dellsam34, I have been listening to feedback from users. Now since last week I have new revision DD emulator PCB (pictures below), that has slightly modified shape (notch in corner) and mounting positions for 6 x 2.0mm pin header, that mounts directly to main board socket CN3501. It now fits under the head drum without contact to mechanism. ( This solution only, when original DD gearbox removed.). It also has the original 6 x 2.54mm mounting position for ribbon cable. New feature 2 screw holes for mounting if connected remote with ribbon cable. Direct mounting underneath head drum requires no fixing.
Now, that it's available without ribbon cable, the price is lower: USD 63 + USD 10 shipping (most countries). Ribbon cable adds USD 15.


[Attachment 86152 - Click to enlarge]


[Attachment 86153 - Click to enlarge]

[dellsam34]

Very good progress, Have you thought about making them available on eBay? Yes there are fees, but it will give you more exposure to the potential market.

[dellsam34]

It's a wrap ! I did a 1/4 turn for the 2 screws. I did have to tweak the P2 guide after that (snow on top) , nothing i'm not accustomed to. Then again, i don't know the history of this deck, best 10 bucks spent recently.

You shouldn't mess with the P guides, you should've addressed the problem at the head, Becarful now that the head maybe damaging the tape, inspect the entire tape path and make sure there is no curling or uneven tape tension.

[themaster1]

Some unexpected development:yesterday i did shut down/disconnect from the mains,today nothing. Had to go back to them gears again (black:8 turns, white 7). motor shaft in the right position also. Everything works fine even after a disconnect. Also i did unscrew back the two spring-screws. Had to adjust P2 guide again aswell

Here is the rocket science

**See you later emulaters**

[hkorpim]

I am glad to hear, themaster1, that you got it back working again!

[TOM11]

hkorpim I would like to ask something...
If you understand how the dynamic drum works, why don't you go the route of making new gears and creating a step-by-step setup guide?
It's better to keep the DD function than to bypass it, right?

[hkorpim]

Good question, TOM11, I have developed my knowhow of DD system just for developing an electronic bypass. DD system was nice gimmick 25 years ago, but today it really does not provide enough value. For me it is enough to keep my VCRs playing the old tapes and if I need to picture search tape content, I don't mind small stripes on screen, because otherwise the picture is very stable.

My own DD gearbox is noisy: the worm gear is damaged and it jams occasionally. The small gears fo lead ring alignment have cracked - it no longer is capable for perfect picture search.

I have created a device for electronic bypass of DD, that keeps the VCRs running. I have shipped it to many countries.
I have no competence or equipment to produce new gears: I just know, that the gears are too small for 3D printing, and to create them from metal, involves a cost nobody is prepared to pay.
I have created a few videos to support people, who have purchased my 'DD emulator' and I hope, that they are useful also for those, who want to refurbish their DD system.

[dellsam34]

hkorpim I would like to ask something...
If you understand how the dynamic drum works, why don't you go the route of making new gears and creating a step-by-step setup guide?
It's better to keep the DD function than to bypass it, right?

I'm working on that project but don't hold your breath, it may take me forever as I'm doing this besides other things in life, designing, choosing the right resin and printing gears is a trial and error process, it may be perfected one day or it may never happen.

[TOM11]

hkorpim:
Thank you for your explane...
It si good job too.

dellsam34:
That sounds very interesting.
We shall see...
Let us know...

[TOM11]

Does anyone have a list and dimensions of the gears and shafts from the dynamic system?
Someone wrote that they had the gears modeled in Solidworks...

[dellsam34]

For that size, dimensions are useless, You need to scan the gears with a 2D scanner or even better yet a 3D scanner and work the shape of the gears and their teeth from an image in Solidworks, Then you apply the scale based on the outer diameter of the gear. In other words, it doesn't work like designing big parts.

I approached the eBay guy selling the gears to see if he can share his design but he did not respond.

[TOM11]

Do you think this item?:

https://www.ebay.com/itm/326193312552

I'm interested in this distance...
How many mm can it be?

[Attachment 86265 - Click to enlarge]

[Alex9876]

Do you think this item?:

https://www.ebay.com/itm/326193312552

I'm interested in this distance...
How many mm can it be?

[Attachment 86265 - Click to enlarge]

Approximately 1,2...1,4 mm

[TOM11]

Thank you Alex...
Maybe a custom steel sleeve with a bolt and nut could be applied directly...
But maybe then a plastic wheel with metal parts would be too heavy...
What do you think?

[Alex9876]

Thank you Alex...
Maybe a custom steel sleeve with a bolt and nut could be applied directly...
But maybe then a plastic wheel with metal parts would be too heavy...
What do you think?

Bolt and nut... Hmm... Why? After all, there are excellent original shafts. The mechanism is completely recoverable if the teeth on the gears are not lost.
The combination of nylon and metal is a bad idea. But no one thought that VCRs would work for more than 20 years))

[TOM11]

Bolt and nut... Hmm... Why?

It seems to me a safer solution than a rope with glue.
But I might be wrong...

But no one thought that VCRs would work for more than 20 years))

It probably depended a lot on the usage.
There are cases when a customer complained about a dynamic drum even during the warranty period.
But it is true that we can be happy that these machines are still here with us.

[Alex9876]

[QUOTE=TOM11;2770870]

Bolt and nut... Hmm... Why?

It seems to me a safer solution than a rope with glue.
But I might be wrong...

I have already repaired 2 VCRs with a rope and glue. I have not yet come up with anything else for home repairs. It is clear that this does not look professional. But it works for now. The question is how long does it work? But I have no answer to this...

[dellsam34]

There are cases when a customer complained about a dynamic drum even during the warranty period.

Never heard of such claims, anything to back it up?

[TOM11]

Is it important to cite a source after more than 20 years?
There have been such cases and it's the same as with everything = nothing is perfect.

[dellsam34]

Has nothing to do with how long ago, Reading it online doesn't make it true, unless there is credible sources. It's like saying X or facebook posts are facts.

[TOM11]

It probably doesn't matter if 1 DD or 100 DD got damaged in the first two years of production from all the world.
Or do you think that's important for some statistics in 2025?

P. S.: I don't mean it in a bad way, I'm just asking...

[dellsam34]

I'm thinking of none, unless you happen to be a tech back then and seen a failure pattern, or you have a christal ball.