Power switch

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Macs

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I took the deck back out and looked at it close with a magnifying glass. I did find a crack on this plastic wheel in the picture.
I got some pictures of the belts, they seem to be riding fine but obviously not engaging something.
I tried to rotate the fly wheel till it reset and I think it did but then nothing worked for a bit. Pressed play and it tried and died. Then the old ticking came back. I guess I’ll be looking for what ever that cracked wheel is.
Thanks for looking, any help is appreciated.
 

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Macs

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I’m guessing that’s probably it.
im thinking of trying this adjustment.
 

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hopey

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You should be able to confirm by rolling this idler with your finger. This should reset the mechanical logic. Normally you can do this with out power then you will understand the reset process. I would clean up the idler tire with sand paper as this gives a fresh rubber surface to grip on the flywheel.

You maybe able to repair the spilt end cap by removing and placing in a vice and plastic weld with a soldering iron.
 

Macs

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You should be able to confirm by rolling this idler with your finger. This should reset the mechanical logic. Normally you can do this with out power then you will understand the reset process. I would clean up the idler tire with sand paper as this gives a fresh rubber surface to grip on the flywheel.

You maybe able to repair the spilt end cap by removing and placing in a vice and plastic weld with a soldering iron.


Excellent, thank you. I’ll try it.
 

Superduper

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Ok I think I see now what is going on.

#1, forget about the adjustments to FF and RW, I don't think it has anything to do with your issue. If they were fine, you might create more issues by changing the setting.
#2, although it's common for idler wheels to create issues on many boomboxes if they are deteriorated, the M70's don't really seem to have this issue so much. Ignore this for now and address the following first:
#3, upon closer inspection of your images, I can clearly see that the microswitch that turns the motor on is the "engage" position. This is the switch that looks like a stack of leafs with a black tail. If you depress the play button and look at the linkages on the back of the deck, you can see the linkage contact and push the switch down. When you depress the stop button, the linkage retracts and disengages the switch. Yours might be broke. I'm presuming that the photo is of the deck in neutral position and not play right? If in stop mode, that metal linkage with the 2 springs should not be contacting the switch (I can't tell if it's pushing it down or not due to the angle). NORMALLY, when you press stop, that linkage disengages the switch, the captsan rotates around just enough to reset the deck and stops. However, if that switch is broke and constantly supplying power, the deck will go around until resets, then starts again which may explain the constant clicking. It's cycling trying to power down but can't because the switch won't allow it to. If that linkage is actually depressing the switch but all the buttons are in the up position, then you have a linkage issue.
#4, as for the crack, don't try plastic welding it -- you are most likely going to just melt the thing into a blob after which you'll wish you didn't follow that advice. It may not even be an issue as long as it's still holding and not popping off the pin. Fix #3 first and if that idler is an issue, then deal with it.
 
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Macs

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Ok I think I see now what is going on.

#1, forget about the adjustments to FF and RW, I don't think it has anything to do with your issue. If they were fine, you might create more issues by changing the setting.
#2, although it's common for idler wheels to create issues on many boomboxes if they are deteriorated, the M70's don't really seem to have this issue so much. Ignore this for now and address the following first:
#3, upon closer inspection of your images, I can clearly see that the microswitch that turns the motor on is the "engage" position. This is the switch that looks like a stack of leafs with a black tail. If you depress the play button and look at the linkages on the back of the deck, you can see the linkage contact and push the switch down. When you depress the stop button, the linkage retracts and disengages the switch. Yours might be broke. I'm presuming that the photo is of the deck in neutral position and not play right? If in stop mode, that metal linkage with the 2 springs should not be contacting the switch (I can't tell if it's pushing it down or not due to the angle). NORMALLY, when you press stop, that linkage disengages the switch, the captsan rotates around just enough to reset the deck and stops. However, if that switch is broke and constantly supplying power, the deck will go around until resets, then starts again which may explain the constant clicking. It's cycling trying to power down but can't because the switch won't allow it to. If that linkage is actually depressing the switch but all the buttons are in the up position, then you have a linkage issue.
#4, as for the crack, don't try plastic welding it -- you are most likely going to just melt the thing into a blob after which you'll wish you didn't follow that advice. It may not even be an issue as long as it's still holding and not popping off the pin. Fix #3 first and if that idler is an issue, then deal with it.

here is a picture of the switch
 

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Macs

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Just to report. The clicking went away at some point. I think after I sanded some of the wheels. Sorry I don’t have all the name of the part down yet.. so now all that’s going on is the capstan just spins, and won’t stop.
 

Superduper

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Sigh... I hope these pics helps you, because I'm done here.

Play ON: If yours looks like this, it will run FOREVER because the switch is ON.
IMG_8169.jpg

Deck STOPPED.IMG_8170.jpg
 
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Macs

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I don’t see where my switch is broken. I looked with the magnifying glass, it looks intact.
If it is broken, then what ?
No replacement parts ?
You would think with this being such a common box there would be answers.
I would like to add, the clicking only happens when this is plugged in. I’m don’t know what that means yet.AAD6E561-AD22-454F-A2F4-B07CE6802E6E.jpeg
 

hopey

Member (SA)
I think your close the idler has 4 positions maybe keep rotating it more. You want to actuate the lever for the reed switch which sets it to normal position.

Check the voltage from the power switch if high resistance ( voltage drop) it can create problems with the music search function. (Brother board above pic)
 
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Macs

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I think your close the idler has 4 positions maybe keep rotating it more. You want to actuate the lever for the reed switch which sets it to normal position.

Check the voltage from the power switch if high resistance ( voltage drop) it can create problems with the music search function. (Brother board above pic)
Thanks for responding,
I have the idler at position 3. It has good grip I feel. I’ll back it back down later if it has nothing to do with the situation. I also don’t want to add pressure on the cracked plastic piece.
I can push the leaf on the switch down to click it off but it wont stay. Maybe it is broken back in the plastic part…
I’ll figure out how to check voltage on the switch. The voltage on the box is set to 120V. That’s correct for N America right? Or 110v ?
I’ll try on batteries if they can stay in the chassis. Thanks again.
 

hopey

Member (SA)
Thanks for responding,
I have the idler at position 3. It has good grip I feel. I’ll back it back down later if it has nothing to do with the situation. I also don’t want to add pressure on the cracked plastic piece.
I can push the leaf on the switch down to click it off but it wont stay. Maybe it is broken back in the plastic part…
I’ll figure out how to check voltage on the switch. The voltage on the box is set to 120V. That’s correct for N America right? Or 110v ?
I’ll try on batteries if they can stay in the chassis. Thanks again.
I mean the DC voltage at the Power switch.
 

Macs

Member (SA)
I checked voltage with batteries in and it was a 5.9 V at the tape power switch.
How do i confirm if the switch is broken? Should I be able to see anything ? Or should I take the switch out and look for something?
And what cheap parts box should I look for to get a replacement switch out of? If anyone knows ?
As far as re setting the deck, I don’t know.. Iv turned the fly wheel a million times. I dot feel any reset. Should it be with the play button engaged? I tried everything. I plays,ff, rewind, record.. but when it just sits there and the capstan is still going then the clicking happens.

Anyway I need answers on the power switch before I brake it trying to see if it’s broken
 

Superduper

Moderator
Staff member
Listen, look carefully at the photos. When the 2 top contacts are touching, the electrical connection is complete and current will flow. In this condition, the switch is ON and the motor will be running regardless of what the deck keys are doing.

When the contacts (top and middle) are no longer touching, the switch is OFF, electrical connection is broken and no current will pass. This is where the switch should be when all the keys are in the up position.

You can measure continuity between the two top terminals if you wish to electrically confirm what I'm saying although you can visibly see exactly what I'm saying. As to whether or not the switch is broken, that depends on whether the linkage lever is depressing the switch. You can't see this from the front of the deck, you have to look at the back. It's easy to do, just depress the play button while looking at the back of the deck. You should see the lever above the switch sink. When that linkage depresses the switch, it should turn the switch ON. However, if the switch is in the ON position without the sliding linkage touching it, then it is broken because it is not working like it is supposed to be. Broken doesn't necessarily mean you see a mechanical break somewhere, it simply means it's not functioning properly. That's a complicated switch. There is two parallel planes. When you flex those two planes, the upper one can't stretch so the lower one has to compress. This compression is what causes the middle leaf to deflect, snap up and touch the top leaf.

THIS BOOMBOX HAS BEEN OBSOLETE FOR DECADES. JVC does not sell parts to repair it anymore. If the switch is broken, you will need to devise a solution yourself so that when the linkage is depressed, a switch will turn on. Replacement leaf switches are available, just not an exact JVC part. Every member collector here knows that unless you can find used parts, you often have to engineer some solution to keep these things running. Sanding wheels is not a JVC sanctioned service technique. Only because replacement parts are hard, often impossible to find.

As for the clicking, you are losing the forest from the trees. The deck motor is not intended to constantly spin with all the deck keys in the up position. Who knows if this is a consequence of that. You need to address things one at a time, I think I hinted as much. Keep in mind that this deck has a solenoid that will definitely click when it is actuated. I believe it is a stop solenoid for the music search feature but might also function for the deck stop too for end of tape. Are you operating the deck without a cassette tape in the chamber? If so, then the autostop probably is actuating. Regardless, only you have the deck in front of you, you'll need to check operation on the workbench to see if everything is working properly. We can't see what's going on with simply a few photos. If you think this is over your head, you might have to just send this off to a technician or maybe buy a used deck.

Hope this helps, good luck on the repair.
 
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Macs

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Should I try to bend the middle leaf to snap in the right direction/down ? I know it’s risky.
the linkage is working as it should and there is no physical brake in the the brass leafs.
It’s just snapping up instead of down. Just wondering if that’s possible.
it’s not electro magnets is it?
It’s a spring leaf.. I wonder what happened ? It got weak with age maybe or it was left for decades with the play button depressed..
 
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