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  #101  
09-17-2020, 05:33 PM
x77x x77x is offline
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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
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  #102  
10-03-2020, 07:38 PM
clueless clueless is offline
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Quote:
Originally Posted by Blackout View Post
Edit: ok i have figured it out! problem solved!!!!

there are small black gears that jamm below the heads. they adjust the head angle. look at the second pic i have posted, i am pointing at them with the tip of my screwdriver. all you need to do is turn on your VCR whilst giving these black gears a roll with your finger...and they will jump to life and reset. And your VCR will stay on@!!!!!

then its a matter of dropping some grease on the gears.

my unit is now up and running but i wander if it is just a jammed gear issue long-term or rather more serious in that the solenoid that runs the gears might be worn. time will tell over the upcoming days...but this is a great result !!!! please try this with your units

@ 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!
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  #103  
11-23-2020, 12:24 AM
jfque jfque is offline
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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.
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  #104  
02-05-2021, 05:14 AM
MarcNijmegen MarcNijmegen is offline
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Quote:
Originally Posted by Blackout View Post
there are small black gears that jamm below the heads. they adjust the head angle. look at the second pic i have posted, i am pointing at them with the tip of my screwdriver. all you need to do is turn on your VCR whilst giving these black gears a roll with your finger...and they will jump to life and reset.


Amazing! Even after almost ten years, this did the trick immediately for my VCR! Thanks so much!!!
Greetings from The Netherlands
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  #105  
02-05-2021, 07:01 AM
volksjager volksjager is offline
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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
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  #106  
02-14-2021, 04:44 PM
jvckeeper jvckeeper is offline
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Quote:
Originally Posted by volksjager View Post
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.
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  #107  
02-20-2021, 04:25 PM
jvckeeper jvckeeper is offline
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Quote:
Originally Posted by jvckeeper View Post
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
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  #108  
02-20-2021, 05:44 PM
latreche34 latreche34 is offline
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An updated version is here.
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  #109  
03-07-2021, 12:36 AM
zxck zxck is offline
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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.
IMG_2725.jpg
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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.
IMG_2730.jpg

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.
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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.
IMG_2734.jpg

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


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  #110  
03-07-2021, 03:19 PM
latreche34 latreche34 is offline
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I've answered your post in the other forum, Here is a copy:

Quote:
Thanks for the test feedback, really appreciated, your problem seem to be worse than any problem I've seen before, I have one machine on the bench and I will inspect the worm gear shaft for cracks after seeing this, You brought up an interesting set of questions.

1- I don't know if the frequency of the pulses matters or not unfortunately, That is something the JVC engineers would know for sure but we can always find out by experimenting, I believe the motor sensor is just a self check that the motor is alive, and second sensor is what actually counts the degree of movement in either way.
2- I would assume so, A sensor means a signal feedback, no signal equals a problem in the processor language.
3- I have not tried, I thought about it though but would require some electronic and coding skills and understand the processor circuit diagram, Basically a small circuit has to be built to generate the necessary tones to mimic the sensors' feedback and fed with the same voltage available to the DD PCB, Then all the gears and motor are removed and the new PCB will sit in place of the DD PCB.

All what you can do is keep experimenting, Try to find a way to make the second sensor register a signal, I'm pretty sure that's the reason for the shutdown.
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  #111  
03-14-2021, 12:26 PM
zalgon26 zalgon26 is offline
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Quote:
Originally Posted by tommytom View Post
Just have to say that helped me fix my very odd problem I was having trying to fix a high end VCR - thanks.
The bright light of the room with cover off was messing up with tape loading.
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!
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  #112  
03-14-2021, 12:33 PM
zxck zxck is offline
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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!
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  #113  
03-14-2021, 02:27 PM
latreche34 latreche34 is offline
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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.
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  #114  
03-14-2021, 04:43 PM
zxck zxck is offline
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Is it the two places marked in red on this photo?
IMG_2796-a.jpg

Here are close ups.
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  #115  
03-15-2021, 01:23 PM
latreche34 latreche34 is offline
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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.
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  #116  
05-22-2021, 05:02 PM
x77x x77x is offline
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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...)
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  #117  
05-22-2021, 09:25 PM
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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.
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  #118  
05-23-2021, 02:20 AM
latreche34 latreche34 is offline
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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.

Last edited by latreche34; 05-23-2021 at 02:58 AM.
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  #119  
05-23-2021, 03:35 AM
latreche34 latreche34 is offline
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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.




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File Type: jpg IMG_3281.jpg (80.8 KB, 28 downloads)
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  #120  
05-23-2021, 05:11 AM
latreche34 latreche34 is offline
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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.



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