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JVC VCR HR-S4700U quickly powers down

J

Jumbaliah

Jan 1, 1970
0
Hi,

I recapped my powersupply with panasonic FC series (low esr 105deg)
electrolytics in my JVC HR-S4700U about a month ago. I have used the
tuner since then without problems. My problem now is that the VCR
doesn't work well with tapes. I've got the service manual and I've
recently replaced the following:

Loading belt
Pinch roller
Mode Switch (didn't realize I could have cleaned my original)
Capstan Gear (original had cracked but still seemed fine - better to
change it)

In the manual there is a procedure to check the main deck without the
cassette housing. Once the housing is out of the way (unobstucted
view of the main deck) you have to disable the End-Sensor with an
opaque cover (I used heat shrink). Then connect pins 2 and 3 on the
Deck-Terminal board connector 3 (CN3). I used a computer jumper to
short these pins. Then it says I should be able to select a mode of
operation. It cautions that if I try a reverse direction it will stop
after a few seconds because of the reel sensor.

After setting up the above (without vhs tape) and powering on the VCR
the mode motor spins the worm clutch so the control cam rotates CCW -
about 90 degrees. This causes the Pinch roller to start to drop into
place. It only moves down slightly then stops and the mode motor
reverses direction. The mode motor forces the control cam to rotate
CW until part of it hits the stop on the half loading gear. The
loading belt then just slips on the worm clutch for a second or so and
the VCR powers off.

When I replaced the loading belt I made sure the alignment holes
though the cam/gears matched as well as the half loading and guide arm
assemblies and plate assembly under the main deck.

When I tried testing with the cassette housing and a real vhs tape (no
jumper and heat shrink used) it will either:

1) Load tape. Play the tape but the take up reel doesn't seem to work
as the tape starts snaking it's way all over the place after the
capstan/pinch roller. I quickly hit stop and eject to save the tape.

2) Load tape. Play fine and even play with forward search. As soon as
I hit rewind search it started to pile up tape then sensed something
wrong and shut off.

3) Load tape. I then just hit eject (no attempt to play) and it
doesn't fully reel in the tape and it ejects the cassette.

I looked at the idler gear and it seems fine. The teeth on it and the
clutch assembly both appear fine. The timing belt looks good. I can
rotate the capstan motor and it spins the idler gear via the clutch.

I'm new to fixing VCRs but I've learned a lot more on how they work.
Just not enough to get mine running smoothly. Anyone have any
suggestions?

Thanks,
burnboy
 
Hi,
You need to replace the clutch. I'd have also advised to change the
mode switch but you already have :)

This is underneath the loading mechanism, and when you lift out the
loading mech. make sure that the hole on the black gear to the right of
the ACE head is lined up with the hole at 11.00 (approximately) and
when replacing this part, or else the loading mechanism won't work.

The clutch assembly is not repairable AFAIK so it will need replacing;
the good news is that most common JVC VCR's including the HRD120 and
540 have the same clutch.

Regards,
-A
 
Hi,

Problem is the clutch is "binding" which stops it engaging the gears.

To get to this part, you need to remove the loading mechanism, and two
screws on either side. The assembly can be found in most of the JVC
series so it shouldn't be too hard to find or buy one.

I've seen this problem on mine so its not hard to fix.

Make sure that you align the loading mechanism correctly on
replacement, the hole at 12.00 on the black gear should align over a
small hole in the chassis. If it doesen't then tweak the eject motor
until it lines up, then fix the loading mechanism with the far right
hand screw, check that it works then replace the rest.

regards,
-A
 
M

Mark D. Zacharias

Jan 1, 1970
0
Does seem like a problem with the reel clutch. Bad lubrication prevents it
from switching back and forth properly. They can be fixed, but when you take
them apart they tend to go, "Sproinggg!" and pop parts all over the place.

Mark Z.
 
J

Jumbaliah

Jan 1, 1970
0
Mark D. Zacharias said:
Does seem like a problem with the reel clutch. Bad lubrication prevents it
from switching back and forth properly. They can be fixed, but when you take
them apart they tend to go, "Sproinggg!" and pop parts all over the place.

Mark Z.

When I rotate the clutch manually in a particular direction it does
slide the idler gears into the supply reel. If I change the rotation
on the clutch it just moves the idler gears between the supply and
takeup reels. This test was done with the VCR off. Should the clutch
be able to slide the idler gears into the takeup reel? Does the VCR
have to be in the right 'mode' for this to happen?

I haven't removed the clutch assembly yet but if I was to fix it how
would you recommend I do it? I've read online that you can use rosin
flux to repair clutches. I just wouldn't want to apply fulx to the
wrong spot.

Thanks for the help,
burnboy
 
M

Mark D. Zacharias

Jan 1, 1970
0
Jumbaliah said:
When I rotate the clutch manually in a particular direction it does
slide the idler gears into the supply reel. If I change the rotation
on the clutch it just moves the idler gears between the supply and
takeup reels. This test was done with the VCR off. Should the clutch
be able to slide the idler gears into the takeup reel? Does the VCR
have to be in the right 'mode' for this to happen?

I haven't removed the clutch assembly yet but if I was to fix it how
would you recommend I do it? I've read online that you can use rosin
flux to repair clutches. I just wouldn't want to apply fulx to the
wrong spot.

Thanks for the help,
burnboy

I'm not sure I read you correctly. If the idler gear does not switch
reliably from the supply hub to the take-up hub, then the problem is bad
lubrication on the center shaft of the idler assembly. It's been a while
since I've seen one, but there's a slit-washer or some other retainer set in
a scored "groove" on the metal shaft. Using a small pick or some such, the
retainer can be removed and re-used, but there is a chance that it will be
more prone to failing later. For this reason it's important not to damage
the retainer. When the retainer comes off, that's when the spring-loaded
parts tend to go flying, and then you'll be guessing as to their
re-assembly.

You shouldn't have to mess with the actual felt clutch portion.

Mark Z.
 
J

Jumbaliah

Jan 1, 1970
0
Mark D. Zacharias said:
I'm not sure I read you correctly. If the idler gear does not switch

When I spin the clutch gear from underneath the VCR it will rotate the
idler gears (three gears) on the top of the main deck. These idler
gears have no problem sliding into the supply reel. But if I then
change direction on the clutch the idler gears will slide out of the
supply reel and stay between the supply and takeup reels (not engaged
to either reel) to freewheel. I take it this is why the tape is
snaking it's way around the VCR after the capstan and pinch roller.
reliably from the supply hub to the take-up hub, then the problem is bad
lubrication on the center shaft of the idler assembly. It's been a while

I'll look at it right now and see what I can find.
since I've seen one, but there's a slit-washer or some other retainer set in
a scored "groove" on the metal shaft. Using a small pick or some such, the

This is in the clutch or the idler assembly? I think your refering to
the clutch, right?
retainer can be removed and re-used, but there is a chance that it will be
more prone to failing later. For this reason it's important not to damage
the retainer. When the retainer comes off, that's when the spring-loaded
parts tend to go flying, and then you'll be guessing as to their
re-assembly.

So what would I acutually be repairing in the clutch? That is if I
can get it open without loosing small parts.
You shouldn't have to mess with the actual felt clutch portion.

Mark Z.

Thanks for your help Mark. I recall getting advice from you when I
was trying to fix my SMPS a while back.

burnboy
 
J

Jumbaliah

Jan 1, 1970
0
Mark D. Zacharias said:
I'm not sure I read you correctly. If the idler gear does not switch
reliably from the supply hub to the take-up hub, then the problem is bad
lubrication on the center shaft of the idler assembly. It's been a while
since I've seen one, but there's a slit-washer or some other retainer set in
a scored "groove" on the metal shaft. Using a small pick or some such, the
retainer can be removed and re-used, but there is a chance that it will be
more prone to failing later. For this reason it's important not to damage
the retainer. When the retainer comes off, that's when the spring-loaded
parts tend to go flying, and then you'll be guessing as to their
re-assembly.

You shouldn't have to mess with the actual felt clutch portion.

Mark Z.

Alright, I think I have it figured out. The more I looked at it the
more it seemed like the problem was the idler assembly (part#
PU61246). The clutch had reasonable resistance both directions. I
couldn't find anything mechanical to stop the idler assembly from
sliding into the takeup reel like it would with the supply reel. You
can see a picture of it here:

http://studiosoundelectronics.com/idlers.htm

I removed the idler assembly and noticed the mechanism to get the
gears to move to the supply and takeup reels was a piece of felt
between two nylon parts. The idler assembly has three gears. Two
white plastic gears and a black plastic gear. One white gear meshes
with the supply reel, the other white gear with the takeup reel. The
third gear (black plastic) meshes with the clutch. They are arranged
in a triangle with the white gears mounted on a nylon bracket. This
bracket pivots about the axis of the black gear. Between the nylon
bracket and the black gear is a piece of felt and what looks like a
nylon washer that is locked to the black gear.

So, the clutch rotates the black idler gear which rotates the bottom
nylon part (washer type piece). The friction between the bottom
nylon, felt, and top nylon bracket pivots the two white gears left or
right to mesh with the supply or takeup reels. Once meshed then the
felt slips on the nylon parts as the tape is in forward or reverse.
So what looked to be my problem was the felt didn't provide enough
friction to allow the idlers to pivot to the right and mesh with the
takeup reel.

I 'fixed' it by squeezing the two nylon parts together to squish the
felt and rotated it back and forth to test it out. It now will pivot
in both directions. I'm thinking that I should replace the felt. Can
I use regular felt from a fabric store?

I still had problems getting the VCR to work as per the service manual
when the cassette housing was out of the way. It makes me wonder if
I'm ment to manually load a tape or a dummy tape in this setup.

Things look good, Thanks for the help guys.
burnboy
 
M

Mark D. Zacharias

Jan 1, 1970
0
Things look good, Thanks for the help guys.
burnboy

The ideal solution would be to replace the part if you can find one. It
appears I was thinking of a slightly different JVC clutch ass'y. I don't
think replacing the felt is any better than what you've already done, either
way the tension may be wrong enough to cause trouble.

Mark Z.
 
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