i have a dream!!!!

or a theory really...

maybe it isnt the gears at all...
if you disassemble the whole thing theres that little motor on the board... maybe the motor is just shit

not enough ass to move whole shindig

Thanks, genious!
 

@ Blackout: Thank you very much for sharing this incredibly clever solution.
@ KPmedia: Thank you very much for creating and maintaining this really useful community and attracting the right talent.
Even though this conversation is so many years old, I encountered the same problem now with my old VCR, and having nothing to lose, I went ahead and tried fixing my VCR based in your conversation. You may believe my screen-name, and yet, my VCR works again. :)
Many thanks!

I confirm this has worked on my JVC HR-S8500MS. Great tip! Although a note. These gears seem really stuck and not moving at all, so you have to patient, try several time, without forcing either, and don't expect they will spin, just moving a tiny bit seems to be all it takes.
In any case, thanks a lot.

Helped a LOT, thanx!
 

Amazing! Even after almost ten years, this did the trick immediately for my VCR! Thanks so much!!!
Greetings from The Netherlands

this "fix" wont last - the plastic gears are cracked and it is only a matter of time until they get stuck again.
no replacements are available - this is the eventual fate of all Dynamic Drum JVC decks - use them sparingly

This post just helped me get my HR-S4500U restarted after it suddenly stopped and then would not stay powered on but it keeps reoccurring. So I guess this machine is not very useful.

Weird thing, this is right after my Sony SLV-N55 ate a tape and then stopped working.

I still have a GEVG4269 that works.

So perhaps this is a fix: http://www.digitalfaq.com/forum/vcr-repair/9777-jvc-dynamic-drum.html

I tried this ultimate fix as posted over at VideoHelp, but sadly got less than ultimate results.

I have a JVC HR-S7600U that I picked up for what I thought was a good price. With a solid cleaning, it played my test tape well. A few months went by and when I finally tried to use it for a project I got the dreaded "shuts down in 3 seconds and flashes Auto."

I followed this tutorial and indeed found one split gear, and another on it's way. I removed the recommended gears, backed off the other 2, reassembled but the same problem remained.
Attachment 13190
Attachment 13185

I occurred to me that I had never heard the whir-whir that others talked about, so I dug a little deeper. It turns out the small DC brush motor was stalled. I was able to remove it and the circuit board, and cleaned and lubed it. With 5V on the bench it spun fine.
Attachment 13187

After reassembly into the gear train, I tested it again and got a distinctive clicking or knocking. After I removed power and restarted it, sometimes it would spin, other times it would stall.

Removing one gear at a time to determine the source of the clicking, I eventually determined that it was coming from the horizontal shaft with the worm gears. A very (very) close inspection revealed that the center worm gear was cracked, and that one of the teeth was cracked and shifted. This would account for the rhythmic clicking, and that the motor would jam on this tooth when stopped and not be able to restart.
Attachment 13186
Attachment 13188
Attachment 13189

Knowing that the VCR would never operate without the motor (and optical sensor), I decided to pull the shaft and worm gears out and let the motor free run with no load of the gear train. Sadly this had absolutely no effect on the operation. While I do now hear the whir of the motor, the VCR still times out at 3 seconds and shuts down.

I do see that at the final stage of the gear train is another optical sensor, and the last gear has a feature that obscures the sensor for half it's rotation, and then gives a clear view of the sensor for the other half. I have tried the gear in both positions and it doesn't make any difference.
Attachment 13191

So now I have several questions:

1) With no load is the motor spinning too fast and affecting the timing sensor?

2) Does the 2nd optical sensor have any affect?

3) Has anyone found a way to defeat this circuit in it's entirety so that the vcr thinks everything is operating nominally?

After so many disassemlies and reassemblies hoping for the silver bullet, I'm at my wits end!

THANKS

I've answered your post in the other forum, Here is a copy:

old answer saves new day
 

Thanks Blackout for original answer and Tommytom for quoting it. A couple of hours (repeatedly loading tapes and searching forums) trying to get JVC HR-S7600U to stop powering off after starting to play a tape automatically (tab out or not) too fast and sending no video out signal. Close the lid! Who knew? At night with lid off the tapes played normally, then in daylight no go. Had the lid off to clean tape path, left it off to watch suspect tapes in transport. Isn't the help of anonymous people on this worldwide web wonderful!

Where are the optical sensors that only allow the machine to operate with the cover on? Does anyone have a photo of their location on the board? Thanks!

They are on the sides of the tape basket, The light diode is in the center of the tape shell cavity, usually it's pinkyish in color.

Is it the two places marked in red on this photo?
Attachment 13230

Here are close ups.
Attachment 13228
Attachment 13229

Yes, And there is another sensor on the opposite side of the tape compartment, In total two black sensors and white light diode in the center.

its been so long since i tore it down... couldnt you just remove the 2 final gears so theres no actual weight load?

im pretty sure thats what i ended up doing... finding neutral and removing the gears that push up

i still think a fresh motor replacement might help
(or its not getting the proper voltage...)

On this PC that I am writing to all you on, a few years ago I spilled a soda on it and I didn't check and some of the soda spilled under the PC. The PC was trashed. I was told one guy in my area can fix any PC. So I gave him the machine, I was like I don't care what it costs just fixed this computer. So he did. This is what he did, he went out and purchased another laptop and just removed the hard drive. I was like really? I could have done this myself.

In some of these cases, in stead of wasting time on a crapy vcr aka S7600 just go buy another unit. The JVC 9900 is so much better than this 7600.

On a side note, I had the JVC SR-V101US and I took the heads out of a 7800 and tried to put that in to the JVC SR-V101US and it didn't work.

One time I found a company that sold these gears and I purchased a set for like $225 and than had to pull apart the heads and install it. That worked.

It doesn't matter what VCR he gets, All gears will eventually fail at a certain point in time, Plastic around a metal shaft was a bad design idea since metal doesn't shrink over time but plastic does. Whether the engineers knew about it or not the design should be fine for the amount of service time the VCR was designed for, 5-10 years tops. We are talking 3 decades here, So regardless what VCR is, the problem should be addressed.

Now, it's clearly that the VCR above needs the second gear with half moon flap to spin and since the worm gear shaft is cracked that cannot be accomplished, What I'm going to suggest requires some skills if you are up for it, It requires some soldering skills and the process is reversible, The idea is to feed the second sensor wires with a pulse signal from the motor sensor, So the motor will activate both sensors at the same time. This may not work if pulse frequency is important, but for the sake of providing active signal it should do the trick of preventing shutdown due to absence of sensors pulses.

I'm in the process of studying the schematic... will get back soon.

Each sensor has 4 pins, 1-2-3-4. Two for the photodiode light source and two for the photocell, Obviously 3 and 4 are grounds for both the diode and the cell, That leaves 1 and 2 as one for the light power and one for the cell pulse feedback.

Attached are both the board itself and the schematic, The two sensors are called Start Sensor and End Sensor as shown in the diagram.

If we assume that pin #4 on the DD board is +5V as indicated by SW5V (possibly switched 5V) so that suggests that pin 2 on both sensors is the photodiode pin and pin 1 is the photocell pin. So the jumper wire has to go between pin 2 of the start sensor and pin 2 of the end sensor so both pins will broadcast the same signal, or simply between pin 1 and 2 of the DD system PCB at the connector.

http://www.digitalfaq.com/forum/atta...1&d=1621759106
http://www.digitalfaq.com/forum/atta...1&d=1621759106

Correction:
Start and End sensors are not part of the DD system, here is another schematic from the same manual, The sensors are called DD_ABS and DD_MFG whatever that means.

http://www.digitalfaq.com/forum/atta...1&d=1621764653