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#1 prg333

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Posted 17 April 2017 - 07:12 AM

I got a JVC M-90 2 1/2 years ago. It was in very good cosmetic shape. I had my friend work on it it took them about 12 hours. He cleaned up all the switches aligned the shortwave FM and AM bands. He also put new belts for the cassette deck. But he couldn't solve the intermittent problem I kept having. It would go through the proper cycle when you turn down the machine and you had a cassette in the deck. It would play but near the end of the tape or sometimes when you would push stop. You get a clattering sound. The audio from tape deck would go off. But it will still continue to play at the normal speed. You could hear the audio if you turn the volume all the way up. It wouldn't respond to any of the keys like stop or pause. It wouldn't even respond to turning off the Radio with the power button. One would have to unplug it to get the heads to drop. Then when you would plug it back in it would work OK.

Now the tape deck unfortunately all of a sudden has just stopped working altogether. You can hear the motor. When the radio is powered up you hear a little bit of clicking.. Then when you try to play the tape deck you just hear the tape deck motor engaging. But it won't respond when you push play pause. You just hear that motor going in the background. I wonder if it's trying to reset the cycle. Appears to me to be a mechanical problem. Not something with the fusible resistors for or belts. Maybe a plastic geer that's slipping because the teeth are getting worn down. So can anybody give assistance please? Anybody have the same problem with their M 90.

#2 Hisrudeness

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Posted 17 April 2017 - 09:41 AM

I've had a couple which acted weirdly when the belts were shot, changing them always fixed the issue.
I'd change the belts first as your first port of call.

#3 prg333

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Posted 17 April 2017 - 11:54 AM

The belts were brand-new the right size when my friend put in the belts when he worked on the M 90. So I don't know if changing the belts will solve the problem. The problem was happening before he changed the belts.
So unless the new belts are slightly the wrong size. It must be another problem. I'm getting some type of mechanical problem mixed with maybe an electrical problem or some kind of problem relating to the Autologic deck. Much more troublesome and then a regular tape deck for example on the M 70

#4 hopey

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Posted 25 April 2017 - 12:47 AM

Sounds like a latching issue. The power to the tape motor should activate when you press play and disconnect when you press stop. These can be out of adjustment and may require bending the metal stops with pliers to modulate correcty. The same can be said with the auto stop function.

This is of course assuming the belts are ok and correct.

#5 prg333

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Posted 25 April 2017 - 07:56 AM

I believe I got the right belts. My friend said they fit well. I can always get a new set just in case. But the problem was happening before he change the belts and cleaned up the machine. So it may be the problem you describe. Is that very difficult to do what you suggested? Would you have to take the machine all apart again? I'm trying to convince my friend to work on it again. I'm not that good with this technical stuff. Taking all the screws out and working on the inside of the boombox I'd rather have my friend do it who is knowledgeable

#6 prg333

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Posted 25 April 2017 - 08:10 AM

Did you actually run into this particular problem with the M 90 that I'm having and do the adjustments, with bending the metal stops ? If so did that help and found the problem with the tape deck

#7 caution

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Posted 25 April 2017 - 09:50 AM

Did you ever fix the broken gear that it came with?

Maybe you should fix that

#8 prg333

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Posted 25 April 2017 - 02:17 PM

I got it working again it's still a bit temperamental. Sometimes you have to turn off the deck when trying to start it by powering off the machine. Then just open the door when the boxes off and then close the cassette door and turn it on again and then the table play fine. Sometimes you have to Disconnect the power plug to get the heads to drop at the end of the tape. My friend looked at the gear and said he wouldn't be able to fix it and less he got an exact replacement gear or cog. Because he said that's where it's probably slipping.

Just wanted to know anyone in this group come across The same type of problems with the tape deck I'm having on my am 90. If so were you able to fix a slip in a gear or replace a plastic cog A tape deck and then solve the problem and have the deck work just as it should?

#9 Superduper

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Posted 26 April 2017 - 01:57 AM

You've asked these question already several years ago and back then, you didn't seem receptive to the advice you received.  However years later you ask for advice again on that same issue but you already concluded that the advice that folks have suggested to you does not apply.  Interestingly, you personally can not provide specific details because only your "friend" whom you trust worked on it.  So if you trust your friend who tells you that the belts are good, and I'm presuming that you've changed all 3 (if memory serves me correct), and I'm presuming that all the pulley and belt surfaces were properly degreased and cleaned, and that everything was properly lubricated (including the solenoid to ensure free movement) as well as head transport assembly, and your friend tells you that it's a gear or cog, and I can already tell you that the cog or gear is already no longer available, then what advice do you want us to give you?


Some of the symptoms you are experiencing are common with slipping belts with this model.  But you conclude that the belts "can't possibly" be the issue.  I've seen belts slip on this model with new belts if they are just a tad too small, or if the belt transport surfaces are glazed or slick (easy to do when handling the belts since they often come in contact with greased parts during the install).  Also, during some parts of the mechanical servo action, there are significant torque humps that the motor and belts must overcome.  This includes start and stop, and head actuation action.  The belts assembly could work fine until it comes up to the torque hump which it might fail to overcome, in which case it may struggle.


Also, you've discounted any possibility of fusible resistor issues.  HOW DO YOU KNOW?  You said you aren't technical and even afraid to just remove the screws.  And yet somehow you can conclude that this common issue likewise does not apply?  Let me just tell you that the fusible resistors in this (and many other boomboxes) have very low values and run hot.  Over time, the values change, almost certainly higher WHICH INTRODUCES RESISTANCE INTO THE CASSETTE POWER CIRCUITS.  There are like 4 of them.  Sometimes they fail open and in that case, certain functions won't work.  However, they don't always fail open, and if the resistance is too high, then the additional resistance might be just enough to prevent the functions from working reliably.  And by the way, the solenoid and even the capstan motor are protected by fusible resistors.  Do you think those 2 items I just mentioned need full power in order to function properly?  After all, isn't the capstan motor which spins the flywheel and provides the kinetic energy to overcome certain servo functions important?


Here's some observations.  Firstly, the microcontroller does not allow more than one function to operate simultaneously.  So if you press a button (say stop) and the solenoid is unable to engage, the controller continues to wait.  In the meantime, no other function is allowed to be processed until the last function is successfully processed.  This is why unplugging the machine is often able to reset the unit.  Also upon power up, the machine always performs a reset.  If it clatters during startup, it means that it is unable to complete a reset.  Also the system also has a stop over-ride switch which actuates when you eject the door.  This is to prevent damage to the heads if they are up when the deck is operating.  If you don't believe me, just try FF or RW or Play and then press the eject button.  The deck will instantly stop before ejecting the door.


Now, since YOU have the boombox, and you aren't qualified or able to work on the unit, and YOUR friend is the one who will do the work, then just go back to him.  And if you can get him to work on it, then you should seriously consider asking him to to heed the following advice:


1.  Check and replace belts if necessary.  Just because they fit doesn't mean they don't slip.

2.  Clean all belt transport surfaces and deglaze if necessary.

3.  Clean all moving parts to ensure free movement, and grease or lubricate where appropriate.

4.  Check that sliding levers are free and don't bind.  This is very important because many functions depend upon free movement of these slide levers, even if their functions aren't immediately obvious.

5.  Check and verify ALL fusible resistors with a low ohm capable meter.

6.  IF you conclude that the issue is a bad cog or gear (which I don't think anyone here has ever seen), then either live with the condition or find a used replacement deck since you aren't going to find the gear from JVC.


Frankly, if you aren't capable of working on the unit, I don't understand why you keep asking for technical advice since you can't perform them anyhow.  Perhaps it's better if your friend comes on here and provide details on what he did, and didn't do and how he came to certain conclusions.  On this model, 95% of the issues can probably be sorted by just following those steps.  And if you ask for advice again, be prepared to be asked how many ohms were those 4 fusible resistors -- because I certainly would be wanting to know.

#10 prg333

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Posted 27 April 2017 - 04:40 AM

Thank you for the very detailed response. I don't mean to discount anyone's advice or opinions. I do appreciate the suggestions. It could be the fusible resistors that you said and some of the other things. I will look over your detailed response and consider some of the things you said. Just cause my friend claims he doesn't think it could be a feasible resister or some other thing besides a plastic cog sleeping gear. He's knowledgeable but doesn't really know this boom box as well as members on this website.

Again thank you for all the advice. Perhaps if somebody from this group who worked on the M 90.I don't know if anyone here would be willing to look over my boombox if I sent it to them and possibly repair the problem. That would be great.

I talked to my friend pinned him down and said he wasn't really 100% sure it was a worn cog, or bad gear. So definitely could be some of those problems listed in the detailed response. I don't mean to sound unappreciative I really am appreciative of the advice people are giving. My friend mostly works tube radios turn tables from the 1940s to the 1970s. So yes he doesn't have much knowledge of two boxes. Especially the more complex nature of the M 90

#11 JVC Floyd

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Posted 27 April 2017 - 07:07 AM

I can tell you this, turning off the power at the switch with the deck running fooks these boxes up eventually,i know trust me lol. If the belts are not on right or are too tight it just won't work right,these decks will drive you fooking mad. I never heard of any case of an m90 having stripped or worn gears. Usually its an electronic part or belts.

#12 Superduper

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Posted 27 April 2017 - 05:49 PM

Most technicians see a boombox and their reaction generally is to recommend just chuck it.  They don't usually view boomboxes as serious audio gear.  Like getting a Ferrari mechanic to work on or take a pinto seriously might be hard.  However, the guys here have the experience to know what the common problems are, especially with well known models like this.  If you are going to be asking questions, remember that someone took time to read and consider and formulate a response or suggestion for you.  The only thing we ask in return is that you, in good faith, put these suggestions into practice before discounting them and ask for "more suggestions please, keep 'em coming," all the while not actually doing anything.  It makes us feel like we are wasting our time.  Several years ago, I seem to recall already having invested time in your threads.  


In my response, I gave you some insight into how this deck works including the micro-controller.  Although it sounds like it's more complicated than say an M70 deck, it's really a better design.  It also has 2-motors (instead of 1 like most boomboxes) so that the reel motor functions only for spinning the reels and the capstan motor's purpose is to spin the capstan and the flywheel which provides the kinetic motion necessary to engage and disengage the heads.  Separating those duties greatly simplifies the deck so that it does not rely on a single motor to perform all of the various duties which means less parts.  I'm sure it's frustrating that it's not working to your satisfaction but you don't sound like you are technically capable of performing the repairs yourself, rather you like to use the product.  Nothing wrong with that, so I suggest that if your friend can't fix it, find another tech, one who specializes in decks perhaps, to help you fix it. 

#13 Rimmer36

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Posted 29 April 2017 - 07:50 AM

The main cog on this deck can fail, it has happened to me twice, but when it fails it results in a continious clunking and the deck can not be used...


go with superdupers sugestions you can't go wrong but first get the whole deck cleaned and lubed followed by new official belts, good luck

#14 prg333

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Posted 30 April 2017 - 04:58 AM

Thank you very much guys for your detailed responses. I really do appreciate that you guys spent the time looking it up and posting the responses. I will try to get a Another tech to work on my box
If I can not convince my friend to work on it again. Hopefully I can get him to work on it.