My working week's just around the corner, so I won't be able to get a photo posted for a few days. But I strongly doubt there's an easy fix. It is 0.5 mm thick copper, forming a cylinder that is a very snug fit around the stator. Absolutely unforgiving of any deviation. As I said, I can fit it back in there but I can't even rotate it by hand. So it might be better to save time/trouble and just spring for a replacement motor. It's about $25, so not a major expense. It looks like someone dismantled an entire JL-B31 and is selling it off in bits, down to the speed control buttons. If I get the motor, I can either solder in the whole thing or grab the rotor and put that into my motor, which is otherwise undamaged.
That is a bush bearing.
You can get new from appliance and car parts stores.
You can use a rubber mallet to bang this back to shape over a mandrel, needs experience.
You can get new from appliance and car parts stores.
You can use a rubber mallet to bang this back to shape over a mandrel, needs experience.
Thanks for the info. I will probably give this TT another chance, but as far as that rotor goes, I'll consider the damage done. So I'll replace the rotor or replace the motor.
Actually, it can be made from Teflon rod as well, but the chance of doing that in Japan, and cost will be difficult.
A piece of heat exchanger tube from airconditioner system will also work.
The usual description for sintered bushes is OD x ID x Length, and Panasonic was one of their big makers, for motors. GKW also makes them in bulk for automobiles, and those are generally in ground final size. It is a relatively easy to find item, many suppliers exist, those are only examples. No ties to anybody mentioned.
Again, 1 piece is the issue, should be available at least from China.
A piece of heat exchanger tube from airconditioner system will also work.
The usual description for sintered bushes is OD x ID x Length, and Panasonic was one of their big makers, for motors. GKW also makes them in bulk for automobiles, and those are generally in ground final size. It is a relatively easy to find item, many suppliers exist, those are only examples. No ties to anybody mentioned.
Again, 1 piece is the issue, should be available at least from China.
I'll post a photo of the part at the weekend, if I remember. It sounds to me as if you are talking about the spindle bearing, which may well be sintered. I took a close-up of that too, and will try to post it. Sintered bronze maybe? I wouldn't know, but it does have that porous look.
The actual damage is to the part that I think would be described as a cup-shaped rotor. This by the look of it is thin copper, and therefore (in the hands of the clumsy) easy to damage. Anyway, perhaps I have my terminology wrong, but I think it's an external rotor, and the service manual itself describes the motor as "Cup-shaped AC Servo-Controlled Motor".
I don't have any experience with machining, nor have I used the services of a shop to have it done for me. I don't know how easy that is here. But anyway, even ignoring possible cost, it's probably a step further than I'd go for this deck, which I picked up for about 2000 yen a year ago. I do hate to see old gear go to the graveyard, especially if I'm the cause of it. But I think I can get around this - once I'd finished beating myself up about it yesterday - by picking up a cheap spare motor for this exact TT, currently available on Yahoo auction. And then I can probably just drop in the rotor in place of the old one, or even replace the entire original motor. If I go the second route, and the speed problem is the same as before, it will be more likely that it's something in the main circuit that needs to be hunted down and fixed.
Thanks for the suggestions and the concern. Much appreciated.
The actual damage is to the part that I think would be described as a cup-shaped rotor. This by the look of it is thin copper, and therefore (in the hands of the clumsy) easy to damage. Anyway, perhaps I have my terminology wrong, but I think it's an external rotor, and the service manual itself describes the motor as "Cup-shaped AC Servo-Controlled Motor".
I don't have any experience with machining, nor have I used the services of a shop to have it done for me. I don't know how easy that is here. But anyway, even ignoring possible cost, it's probably a step further than I'd go for this deck, which I picked up for about 2000 yen a year ago. I do hate to see old gear go to the graveyard, especially if I'm the cause of it. But I think I can get around this - once I'd finished beating myself up about it yesterday - by picking up a cheap spare motor for this exact TT, currently available on Yahoo auction. And then I can probably just drop in the rotor in place of the old one, or even replace the entire original motor. If I go the second route, and the speed problem is the same as before, it will be more likely that it's something in the main circuit that needs to be hunted down and fixed.
Thanks for the suggestions and the concern. Much appreciated.
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Try and get the circuit board as well, save yourself some trouble shooting, and lots of time.
It could be your board is defective, a matched set will be easier to transplant.
It could be your board is defective, a matched set will be easier to transplant.
Part of the troubleshooting is about learning some new things. And there's not a lot of money at stake here. I'm not great at trying to understand circuits but every audio component I open does teach me something - with most of the credit going the input and assistance of others, of course.
Rather than getting another circuit board, I can probably find this whole turntable for close to the price I bought it last time - I know a few places to look, though it may take a few months to find one. On the original, I have restored the plinth, which after re-veneering looks pretty good, to me, so a working JVC could be plopped right in there. But l also like the idea of saving the original deck and giving it a new life: in the end it's not really about money or the fastest way to get a working table. That's why I may put some time into trying to revive it rather than just ripping whole sections out and replacing them outright. Alright, the rotor/motor is such a replacement, but that was after I rendered the rotor inoperable. If it hadn't been for that accident, I'd still want to be working with the original part.
Rather than getting another circuit board, I can probably find this whole turntable for close to the price I bought it last time - I know a few places to look, though it may take a few months to find one. On the original, I have restored the plinth, which after re-veneering looks pretty good, to me, so a working JVC could be plopped right in there. But l also like the idea of saving the original deck and giving it a new life: in the end it's not really about money or the fastest way to get a working table. That's why I may put some time into trying to revive it rather than just ripping whole sections out and replacing them outright. Alright, the rotor/motor is such a replacement, but that was after I rendered the rotor inoperable. If it hadn't been for that accident, I'd still want to be working with the original part.
So here are some of the shots I took of the rotor and the bearing area. The bearing looks like sintered material, bronze maybe?
The cup rotor is misshapen, so I will just take the new part I ordered and try to fit it this weekend I hope. Then I'll be back to where I was before, a deck with speed issues! I'll go back over the posts upthread, read the suggestions, and do whatever checking and testing I can from that, or ask questions where I don't understand.
The cup rotor is misshapen, so I will just take the new part I ordered and try to fit it this weekend I hope. Then I'll be back to where I was before, a deck with speed issues! I'll go back over the posts upthread, read the suggestions, and do whatever checking and testing I can from that, or ask questions where I don't understand.
If the rotor may still be accomodated into the core, I suggest continue using it until repaired completely, and replace by the new unit once finished. Else a new accident may occur to the new one with more time and money wasted stupidly.
Unfortunately, although the old rotor can be inserted (just), it can't spin. So it's not much use. That being the case, I'm not sure what you mean about waiting until repaired completely: the repair process needs a working rotor to check the speed with, and the old rotor being damaged beyond my competence to fix prevents me using it at all.
I don't intend to repeat the accident with the new one. One learns. So that just means making sure it is always placed somewhere safe when out of the turntable. Like I said, last time around I managed to find (and damage) the one part of the TT that is really pretty fragile: the thin walls of that external rotor. But there's no way to clean and lube the bearing without removing it, so I just need to remember that extreme care is required.
I don't intend to repeat the accident with the new one. One learns. So that just means making sure it is always placed somewhere safe when out of the turntable. Like I said, last time around I managed to find (and damage) the one part of the TT that is really pretty fragile: the thin walls of that external rotor. But there's no way to clean and lube the bearing without removing it, so I just need to remember that extreme care is required.
If you look closely at the second picture, on the right side, you can see the line of the rim is not perfectly circular. Here's another shot that might make the deformation easier to see. The space that 1-mm-thick cylinder wall has to be inserted into, outside the windings in the third picture and within the circle of, I guess they're magnets (not visible in the picture), is really snug, but there must of course be no physical contact. And if it was undamaged, it would spin freely by hand. Those days are over for this rotor. There's no easy way for a layman to restore it to a perfect circle. (After it hit the floor, it was very visibly dented; this picture is after trying - and I wasn't expecting success - to reshape it.)
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As copper is relatively soft, perhaps you can roughly reshape it and make it possible to run, although imperfectly because the lack of dynamic balance, and so, continue the job in the electronic control untill you get the new one. If the shaft isn't damaged too, I don't see any problem. I want to encourage to give it a try. In any case the no is already put.
This is relatively thin for a sintered bearing, the copper part can be put back in shape by careful use of a wooden or plastic hammer.
Sintered bearings are pressed into shape, like ceramic cups and plates, then fired in a furnace, then machined.
This copper colored object does not look like a sintered bearing to me, more like a grease cup.
Like Osvaldo says, finish the repair before putting new parts.
Sintered bearings are pressed into shape, like ceramic cups and plates, then fired in a furnace, then machined.
This copper colored object does not look like a sintered bearing to me, more like a grease cup.
Like Osvaldo says, finish the repair before putting new parts.
I have a replacement motor now. I bought it for the rotor only. I doubt that I will use the motor itself as a drop in replacement, unless it seems necessary at some point in the future. The wires were cut and look to be on the short side, so soldering it in might not be a trivial procedure. I would guess that the old motor is just as likely to be operational.
I will take the rotor from the new motor shortly.
I took some more photos of the bearing and stator section. It should clear up the confusion about parts*, or at least clarify whether I described them correctly. I just need to load them off the camera so I can post them. The service manual diagram shows very little, just the sealed motor unit, so it's really not much help on that. There's nothing in the text either, except the single line in the specs that I already quoted earlier.
* This is my summary of parts we have talked about:
Bearing (sintered) - picture 3 in post 49. The innermost tube/sleeve/bushing in the centre of the picture.
Rotor - copper, cup-shaped (or cylindrical if you prefer). This is fitted down, by means of the built-in spindle, into the bearing. It is an external rotor, so it also fits outside the motor windings and what I assume (tentatively, as I know jack about motors) are an array of electromagnets. Hold on a while, the picture I will post shows those; they're not visible in what I have posted so far. It will also show the narrowness of the space that the cup must fit into. I measured the thickness of the circular copper wall of the rotor as 0.5 mm, and it must fit very precisely into a circular space of (eyeballing it) about 1 mm.
I will take the rotor from the new motor shortly.
I took some more photos of the bearing and stator section. It should clear up the confusion about parts*, or at least clarify whether I described them correctly. I just need to load them off the camera so I can post them. The service manual diagram shows very little, just the sealed motor unit, so it's really not much help on that. There's nothing in the text either, except the single line in the specs that I already quoted earlier.
* This is my summary of parts we have talked about:
Bearing (sintered) - picture 3 in post 49. The innermost tube/sleeve/bushing in the centre of the picture.
Rotor - copper, cup-shaped (or cylindrical if you prefer). This is fitted down, by means of the built-in spindle, into the bearing. It is an external rotor, so it also fits outside the motor windings and what I assume (tentatively, as I know jack about motors) are an array of electromagnets. Hold on a while, the picture I will post shows those; they're not visible in what I have posted so far. It will also show the narrowness of the space that the cup must fit into. I measured the thickness of the circular copper wall of the rotor as 0.5 mm, and it must fit very precisely into a circular space of (eyeballing it) about 1 mm.
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Here's the stator section, orange arrowhead showing the space the copper rotor goes into.
This is the rotor after partial insertion:
This is the rotor after partial insertion:
The inner gray ring in the center of the stator is the sintered bush bearing.
Sintered bearings have pores, which absorb and store lubricant, it is released slowly as the shaft turns, a solid sponge of sorts.
Look closely with a magnifying glass, the pores tend to be small, and the material seems lighter than solid bearings.
I would check both the new and the old motors with an external power supply, before starting the assembly, or at least check for continuity.
The winding resistances should be within 3% of each other on a decent meter with good batteries.
Sintered bearings have pores, which absorb and store lubricant, it is released slowly as the shaft turns, a solid sponge of sorts.
Look closely with a magnifying glass, the pores tend to be small, and the material seems lighter than solid bearings.
I would check both the new and the old motors with an external power supply, before starting the assembly, or at least check for continuity.
The winding resistances should be within 3% of each other on a decent meter with good batteries.
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Part of knowing jack about motors is that I don't have the tools to hand for testing motors.
Can you show the sort of power supply that can be used for a motor like this? A photo/link would do it best.
For testing the motor what you only need is the motor, a filament bulb (40/50W) and the starting/running capacitor. Wire the motor and the capacitor as the maker say (in case of error, the rotor will rotate in wrong direction but no worse thing like this). Hook the filament bulb in series to the motor and energize the set. In case of error or defective motor/capacitor, the bulb will alert you. Ignore all electronic circuitry. Be carefull with live wires (an old professor said me when I was 16: keep always one hand in the pocket).
