Capstan motor gear for JVC HR-S4700U?
 

Hey all, I have a JVC HR-S4700U that has had the capstan motor gear pop off the shaft. Looking at the gear closely, there is a hairline crack all the way through that allowed it to pop off the shaft. I'm assuming that gear is just a press fit on the capstan shaft?

Is it worthwhile to attempt to try and get glue into the crack?

Are their suitable substitutes?

Thanks for any suggestions!

Can you post a picture?

I say it's worth a try. I sugest you degrease really well it and maybe sandpaper it a little and use epoxy glue (or MMA structural adhesive glue)

Other solution plastic welding:

https://youtu.be/HPh_htNOzSY

Here's images of the gear. The crack is oriented on the right side. No tooth loss or any other fractures, just a split all the way through the side.

I started to do that, but I got concerned that I would change the inner diameter of the gear with the epoxy filling in the gap. I can barely wedge a fingernail in there so I'm not sure how much luck I would have with sand paper.

That's pretty neat about the plastic welding. I think I may keep that idea as a last resort.

Any of you that look at the pictures, google rotated the image on me. The crack is at the top...not the right.

If there is a surface that is not in contact with anything one option is to use string or wire or similar in conjunction with epoxy/glue to help reinforce. A sort of last-resort with gears press-fit to metal shafts is also to roughen the shaft with a dremel or similar and glue/epoxy it onto the shaft itself but that might prevent you from being able to disassemble that bit so again is a bit of a last resort option.


If not, variations the mechanism was used in quite a lot of JVC decks from the late 80s and early 90s so finding a cheap vcr with the same mech to borrow a non-broken from, or maybe even finding NOS spare should be doable. Granted maybe this is the gear that the toothet belt goes onto? In which case only some variations of the mech used a toothed belt (others used a normal flat one) it so it's not quite as common though still found in some of the nicer non-svhs variants from the around the same year at least. And also if it's related to the belt drive the that the diameter isn't changed significantly is a bit more crucial than elsewhere in the mech since the take up reel and capstan needs to run in lockstep during playback.

One way is to glue the gear to the capstan shaft and capstan pulley's surface where the gear sits, That way it gives it more support to keep the crack from opening further.

Thanks for the suggestions! I have to admit I didn't really think about gluing the gear to the capstan...was concentrating too much on keeping the press-fit viable I guess.

If worse comes to worse and I have to pillage parts off of other VCRs, any particular ranges would be most likely? The capstan motor is a PU61003-1-2.

I'm afraid that it is almost impossible to close the crack with glue and force the gear back into the capstan and not crack it again, the bond on that small section to be glued is not strong enough to overcome the lateral stress that comes from the press fit.

Thanks for all the suggestions. I ended up using an epoxy to glue the gear to the bottom of the capstan motor and gave it 24 hours to cure before putting the belt back on. I made sure that the epoxy that seeped in with the crack was not interfering with the belt teeth while things were still a little gummy, but everything turned out great. Gear feel solid, belt turns like expected and everything looks to be working.

How does your repair work after some time?

What glue do you recommend to fit the plastic gear onto the capstan motor plate?

When the gear cracked and your HR-S4700 broke down, did your player chew the tape?
This happened to my player, then it shut down.

Were you able to eject the cassette but the magnetic tape got stuck around the tape guides and you had to cut the strip then remove the cassette?

This is the gear that cracks causing playback issues.
Was this a huge problem on certain JVC decks?
I have a brand new NoS HR-S4700 with the same problem plastic gear cracked and the tape was wrinkled around tape guides then player shut down.
My repair tech ordered new plastic gear and fixed the problem, I got my player back, hooked it up, for 30 minutes it played perfect only to chew the tape and shut down.
Now my player is broken and it needs another repair to refit the same gear.

Was this a common issue on specific JVC decks plastic gear breaks from age related reasons?

I used a two-part epoxy to re-attach the gear to the shaft. I put a light amount of the epoxy on the surface that mates with the shaft and a small amount in the crack itself.

While the glue was drying, I made sure that the valley between the gear teeth located at the crack was preserved. The glue did have a tendency of ooze a little initially so very carefully removed some of the ooze using a toothpick.

Past that, I let the epoxy dry for a solid 24 hours. While mine was a quick-set variety of epoxy, it still was moderately gummy for several hours. Once fully cured, it was very solid.

As for the tape issues, yes the gear not in place would cause the deck to eat tapes. I didn't have to cut the tape to get it out, just would carefully pull it back out. Since I was evaluating the deck, I was using a test tape, and the tape did get a handful of wrinkles.

With the epoxy, I can't imagine the capstan gear ever falling off.

Thank you for your quick reply.

You didn't buy a new replacement gear, you re-used the old gear fixing it with glue.
JVC supplies new improved gears perhaps in nylon material or similar?
You haven't had any issues so far after the repair?

Perhaps Loctite has some good special glues used specifically for nylon/plastic-metal use?

Did you see my attached photo of the parts in my previous reply?

That's correct. I did not buy a replacement gear. Looking at the service manual for the VCR, I couldn't see that there was a part number for just the gear. I could only find the entire capstan assembly that would come with the gear already in place.

So far, I have not had any issues. That said, I believe the two part epoxy is the best long term answer. It's a pain to work with, but I think it's worth it for the results.

As to your picture, I did take a look at it, but that looked like just a diagram on what orientation to place the gear on the shaft. Do you have the part number for the new gears?

Happy to hear your machine is functioning perfectly. :congrats:

Parts number is PTU96031-678C

Thank you for the part number. All my searching I never did turn up that association. I had the part number for the capstan and all the ones I saw included the gear with it.