JVC M71 tape play issue

[cappedup]

In love with my JVC boom box. I put it into storage about 3 years ago after leaving work in LA. Have dug everything out and brought it back to NY.

Played a tape and instantly remembered an issue it had when I packed it up. Certain tapes shut off after a minute, or even a few seconds. Like they are tightening up or something.

Im happy taking it apart. Have installed a nice lighting mod, thanks to this forum.

Ive never changed belts on something like this, I'm sure its quite involved. But very happy to tackle that.

Some tapes play fine. Others wont play more than a couple of seconds.

Notes:
Installed lighting mod.
I get a static ’ticking‘ when touching the controls and buttons - connected?

Anyone suggest a course of action?

 

[Tinman]

It could be a clutch issue causing the take up reel to slip before it should and tripping the auto stop.
If you play it with the door open, try stopping the take up reel with your fingers and see how hard or easy it is.
It should take pretty decent force to stop it.
If it's fairly easy to stop, you probably have an issue inside.

Also, I've found that some cassettes don't reel up nicely.
By that I mean the tape edges don't line up as the tape is reeled in.
You can see it on a clear cassette, the tape pushes on the sides of the cassette causing friction.
You can try hitting the cassette on the palm of your hand several times on each side to try and align the tape or FF/rewind the entire cassette which usually gets it back aligned.
This could be why it only happens on certain cassettes.

 

[cappedup]

Fantastic things to try, thank you.
I’ll have a look tomorrow.

 

[BoomboxLover48]

In most cases the clutch assembly lock (plastic piece) will break off.
It will be a good idea to use one from the parts list below:

58 Pcs Plastic Gears Set Shaft Motor Gear Gearbox Robot Toy Kits DIY White Craft | eBay

 

[Transistorized]

Excellent advice being given here. It is very likely that the take up spindle is slipping on cassettes that have a little more resistance internally. Over time the take up spindle can lose torque. Once the take up spindle stops, the counter wheel stops and auto stop circuit engages as per design. A take up which has lost torque can be a failed clutch or hardened take up wheel tire in relation to play clutch drive spindle. Usually, you will find that the clutch retainer has cracked. It is made of nylon plastic which shrinks over the years. It is pressed onto a metal shaft that houses the entire clutch assembly. Once it shrinks enough, it cracks and releases tension of the clutch spring causing it to lose torque and slip. You cannot go by the torque of FF or Rewind because that is driven by an entirely different clutch. If the clutch is not broken and the belt tension is proper, you can adjust the torque of the clutch by rotating the clutch mechanism CW or CCW to adjust tension. But most of the time, the clutch has failed or rubber tire has gotten hard over time.

 

[cappedup]

It could be a clutch issue causing the take up reel to slip before it should and tripping the auto stop.
If you play it with the door open, try stopping the take up reel with your fingers and see how hard or easy it is.
It should take pretty decent force to stop it.
If it's fairly easy to stop, you probably have an issue inside.

Also, I've found that some cassettes don't reel up nicely.
By that I mean the tape edges don't line up as the tape is reeled in.
You can see it on a clear cassette, the tape pushes on the sides of the cassette causing friction.
You can try hitting the cassette on the palm of your hand several times on each side to try and align the tape or FF/rewind the entire cassette which usually gets it back aligned.
This could be why it only happens on certain cassettes.

Clear cassettes seem to be lined up ok.

The take up reel is quite easy to stop when playing.

In fact running in Play with the door open, it clicks off after a few seconds without any tape in.

The reel seems to ‘slip’ rather than slow. Not sure if that’s the case or it’s what my brain is telling me.

Sounds like clutch in any sense, right?

Next question, what’s involved in remedying that?

Edit: just seen further responses above. Many thanks. Fully understand what your saying with the auto stop function kicking in.

Is there a handy diagram that indicates which clutch parts we are referring to? And which is the potentially hardened rubber wheel to look for, etc. great things to check (if I know what they look like.)

 

[Tinman]

I had an M70 and an M71 and both had the cracked retainer that Transistorized referred to.
Both were the ones under the capstan flywheel.
If you look in BBL48's picture, both of those round wheels with the three tipped metal pieces are what we're referring to.
They have springs underneath the nylon pieces on the tops, they're the ones that shrink and crack.
You can actually adjust the spring tension using those metal pieces on the "steps" they sit on.
It's hard to describe but you'll understand if you get in there.

 

[Transistorized]

Here are the clutches and their functions

 

[BoomboxLover48]

See the cracked retainer on top of the clutch assembly in the first picture.
The clutch assembly with spring washer and retainer is shown in the second picture.

The retainer (friction lock tight) cracks and there is no way to fix the crack on it.
One should find a small plastic gear wheel and slip it tight on the stainless-steel shaft to hold the whole assembly in place.
Hold the firmly other end of the cutch assembly axle, when you slip in the retainer. If not, one will easily break plastic swinging arm of the whole assembly.
~Royce

 

[cappedup]

Ok well that couldn’t be more info. Thank you.

I’ll get this thing apart again and have a look.

I like the idea of slipping a random eBay plastic cog on there as a friction fit.

Will report back with pics of what I find.

 

[Tinman]

I've never seen more detailed information on any kind of fix, lol.

 

[cappedup]

Short video of play clutch. Seems ok to me. I don’t see any cracks in the wheel. It seems tight on the stainless spindle.

There is a lot of in/out play on the shaft. Like about 1/4”. Assuming that’s normal as the mechanism needs movement.

The issue has got progressively worse over the weeks and now the play function shuts off after 5 seconds. 2 seconds before it does I can hear a slightly metallic rotational noise which seems in tune with the big flywheel.

These timings are now incredibly repetitive. Always 5 seconds.

Any further thoughts based on this?

 

[Tinman]

I haven't worked on one in a while but I believe in Transistorized's first picture where he's has "play" written, the arrow is pointing to a shaft with a little rubber tire.
That rubber on the shaft contacts the smooth part of the reel with friction and turns it.
If that rubber is hard it can slip and not turn the reel correctly.

 

[Tinman]

Also, make sure the brakes are releasing.

 

[cappedup]

Ok I can imagine how that would make a difference. That looks like the whole thing comes apart for that job.

Brakes releasing? Can I check that before I get deeper into it?

Thanks.

 

[cappedup]

Ok I’m getting somewhere.

The rubber tires on the wheels don’t look too bad.

The unit is now on its side and exposed and I can play a tape without stopping.

However REW now cuts off after about 10 seconds. Which is a seperate clutch.

The only thing that ‘looks’ not great is the fatter tire at the head end of the tape. And that spindle looks corroded.

But everything else ‘looks’ decent.

The PLAY wheel has decent friction, although less than the REW.

With my symptom now switching to the REW with the unit apart, does that indicate a wider motor/drive issue?

 

[cappedup]

I’ve noticed something else.

The large grey flywheel is wobbling. I can steady it somewhat by tightening the screw with the spring under it, on the triangular plate. But realize that’s also adding friction to that system.

I feel like this is significant.

Can the flywheel mechanism cause the unit to shut off, whether PLAY or REW?

I see a video on YT of a guy who fixed this by re-seating the wheel on the shaft.

 

[caution]

These have a somewhat sophisticated auto-stop circuit due to the way it has to work with the Multi-Music Scanner (i.e. stop the tape when it finds a gap between songs) but I'm not sure how it stops the deck at the end of a tape when MMS is switched off. Someone else might have to chime in on that.

 

[cappedup]

Ok, I’m pretty sure my issue is/was connected to the capstan flywheel/MMS system.

My flywheel had movement in and out. (Video). I’ve tightened that up with the screw until it just stops that movement.

Independently, the flywheel has wobble on the shaft or into the little socket thing, this creates a slight rubbing noise on something. That looks like a complete unit disassembly to address, so should I park that problem for now?

In addition, the MMS assembly (I think it’s that) that interacts with the flywheel had one end of a thin spring out of place (photo). I’ve teased that back with tweezers.

In summary. The unit now PLAYs, yay. But REW shuts off after a few seconds. FFW is fine.

Before I put it back together should I be doing anything else?

Thanks for all the help guys.

 

[Tinman]

The fat tire near the head is called the pinch roller.
That "pinches" the tape against the spinning capstan (the shiny shaft) which pulls the tape through at a consistent speed.
The take up reel has to spin at different speeds as the amount of tape in the cassette builds which is why it needs a slip point.
The capstan needs to be clean and the pinch roller needs to be clean and pliable.
After looking at your pics, the shaft that turns the take up reel is metal and the take up reel itself has a rubber tire around it (same on the rew/ff reel).
You have to make sure the rubber is in good shape, meaning both clean and pliable.
Actually, anything that makes contact when play or rew/ff is turning needs to be checked out.
A magnifying glass helps to see if any of the rubber tires are cracked.
There's tons of information on the site on how to check and clean all of this stuff.

Your brake is releasing as shown in your video after you took the tape out and rewound it.
The capstan should have play in it, how much, I'm not sure.
You could be missing a washer or two.
Again, I haven't worked on one of these in years, it's hard to remember.