HERE SHE IS MY NEW NEW JVC M 70 !

[trippy1313]

If I remember correctly, don't you have to remove the screw and the plate that adjusts the speed in order to get to the belt to replace it?


I would get in there, mark the speed screws location and how many spins it takes to remove, change the belt, and put it back together.


I'm sure the belt is just slipping causing the slow playback.

When I did mine, I only took off the two solid screws, Left the adjustable screw, and just rotated the plate out of the way, so it kept the screw/adjustment in the same place, no problems at all with mine.

 

[baddboybill]

Another reason for slow tape speed is pinch roller could be slipping. Check it to see if its clean and still feels like soft rubber. If its hard, dry and cracked it needs replacement. Sometimes it only need a good cleaning


Bad Boy Bill

 

[superlew]

We all want to point you in the right direction, but there are so many variables. You'll never truly know the answers until you get your hands dirty.

Another reason for slow tape speed is pinch roller could be slipping. Check it to see if its clean and still feels like soft rubber. If its hard, dry and cracked it needs replacement. Sometimes it only need a good cleaning


Bad Boy Bill

Check the pinch roller first. Then...
Throw in some fresh belts. Next, adjust the plate on the flywheel. Finally, when you know your belts and plate are perfect, you can adjust motor speed if necessary to really dial it in.
And Bill is right about the azimuth adjustment. If your azimuth is off, your tapes sound like a$$.

As I've said before: Education, Organization, and Patience.

Sometimes I just assume everyone knows what's going on inside these things.

(Now, if I'd only take my own advice. )

 

[autobot84]

anybody have a picture of this plate by the flywheel? would like to see where i adjust the tape speed, mine is going too fast

 

[baddboybill]

anybody have a picture of this plate by the flywheel? would like to see where i adjust the tape speed, mine is going too fast





Bad Boy Bill

 

[autobot84]

thanks bill that helped alot. now they don't sound like pissed off chipmunks

 

[baddboybill]

thanks bill that helped alot. now they don't sound like pissed off chipmunks


No problem


Bad Boy Bill

 

[restocat]

well well well, I've cleaned the contacts again and nothing changes, also the tape speed is a bit faster than it should, not a lot, but a little
now I want to throw it through the window!!! what can i do? it's really annoying these troubles

You could do what me and vladi do. We hook up the boombox to a full home audio system.. line in and you are good to go.
Great looks, great sound, and no mess. Then come back to working on the tape deck when you are relaxed and can get help from other members in France.

 

[autobot84]

the m70 is a breeze to take apart 4 screws holding the top panel on, another 4 screws holding in the case and you have to unplug 2 connectors and 3 wires. its as easy as lacing up a pair of sneakers.

 

[Michiel]

Are you serious? Tuning the speed by the adjusting the friction of the capstan to top bearing? My 70 has a trim pot inside the motor for adjusting.

 

[Superduper]

What are you guys talking about? That plate is for setting backlash/freeplay, not speed. As Michel said, adjust it properly using the motor trimpot. Lets not start doing hack repairs. Overdoing the backlash to slow down the speed introduces load onto the motor which blows regulators and motors.

 

[Beosystem10]

True enough, but the VR wouldn't randomly go off value so that, it appears, is how we've suggested that there is more likely to be some mechanical characteristic such as glazed rubbers or even a dry Oillite bush to cause the problem. That VR setting is unlikely to be in need of adjustment where the device has at some time played at the correct speed.

 

[baddboybill]

If its going to slow then I usually adjust plate first and if that don't help then I adjust motor speed


Bad Bad Bill

 

[Superduper]

True enough, but the VR wouldn't randomly go off value so that, it appears, is how we've suggested that there is more likely to be some mechanical characteristic such as glazed rubbers or even a dry Oillite bush to cause the problem. That VR setting is unlikely to be in need of adjustment where the device has at some time played at the correct speed.

First, the motor mounted pot does often become oxidized and the value can in fact change. Just had that this weekend where the speed on one deck could not be adjusted within range until some deoxit was worked into the pot. These things are 30 years old. In any event, the entire tape transport assembly works together as an assembly. Belt tension, friction in all the rotating assemblies including the pulley's capstan needle, etc, all contribute to the speed. That's why final speed adjustment is performed after everything has been given attention. The motor setting is not intended to stay the same forever. It is intended to compensate for speed variations within that given tape deck. Over time, changes in belt tension and maybe loss of lubrication in some of the bearings, and perhaps some grease getting hard.... makes a difference. You don't compensate for these by cranking down on the flywheel bearing backlash. The backing plate SHOULD be adjusted to the proper amount, but final adjustment should be performed at the motor. If adjustment was performed solely via the backplate, then you could over tighten the nylon bearing and it will soon wear in short order to where speed will once again become an issue again. I don't take issue with all the rest of the suggestions including cleaning pinch roller, etc. I'm only referring to the use of the flywheel backlash adjustment as a means to adjust tape speed -- bad idea.

Remember, these are not complicated motors and the motor speed adjustment circuit is NOT a true dynamic speed regulator that can self compensate for load changes. Regardless of initial setting, changes in load WILL result in different tape speed -- that tiny motor circuit will not self compensate for varying changes, it is intended for setting speed on a stable system.

 

[baddboybill]

I agree Norm and read through post again and for some reason I was under impression the speed was slow. I guess I didn't read it right plus I was on some heavy pain killers last week. but like I said I usually try to adjust plate when speed is slow first then pot on motor .




Bad Bad Bill

 

[BoomboxLover48]

Actually I was wondering how could JVC design motor speed fine adjustments by using flywheel backlash adjustments.
They didn't!

In most sophisticated decks they will give a clearance adjustment of approximately 1mm. That part will have some silicon grease and a teflon stopper mounted on the back plate designed like a cup/cradle for the flywheel axle backlash.

Even Flinstones wont use that for adjusting speed. It is so crude Poor motor!

 

[Superduper]

That's because on some stupid boombox designs like a certain M9994 wannabe, (read: M9990) has no tape speed adjustment. So mechanical fiddling is the only way to tweak the speed on those models. A few smart members have replaced the motor on the M9990 with one that has the internal trimpot = problem fixed.

 

[baddboybill]

That's because on some stupid boombox designs like a certain M9994 wannabe, (read: M9990) has no tape speed adjustment. So mechanical fiddling is the only way to tweak the speed on those models. A few smart members have replaced the motor on the M9990 with one that has the internal trimpot = problem fixed.


JVC 550 is same way


Bad Bad Bill

 

[BoomboxLover48]

I agree Norm and read through post again and for some reason I was under impression the speed was slow. I guess I didn't read it right plus I was on some heavy pain killers last week. but like I said I usually try to adjust plate when speed is slow first then pot on motor .




Bad Bad Bill

Those types of "heavy pain killers" should be banned!

I know some Vodka brands does the same for me.

 

[baddboybill]

Those types of "heavy pain killers" should be banned!


Believe me I needed them. Had been in pain for 4 days before I finally went to hospital.


Bad Bad Bill