OakenShield1 Posted August 9, 2011 Share Posted August 9, 2011 Hi knowledgeable ones I am trying to get my JVC JL-A1 up to speed. The motor is a little tired and I need a thicker belt to get it to the right speed. Does anyone here know anyone that can make one up? It needs to be 200mm x 5mm x 0.9mm thick. I can find plenty to do 0.6mm thick. The current one is 0.7mm. I've tried asking people on flea bay but no such luck. Surely someone out there can make me a glorified rubber band to spec!! I'm not interested in rebuilding the motor as I think it will cost more than the turntable is worth. I am sentimentally attached to it however. TIA Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 9, 2011 Share Posted August 9, 2011 Huh? A thicker belt won't solve the problem. The motor in that old beast is a standard synchronous type. You need to service the motor. The motor can be stripped down, cleaned and lubricated, such that is will as good as new. You should also check the main bearing assy. Just give the platter a spin (with no belt) and make certain it spins freely. If it doesn't, then you may need to address problems with the platter bearing too. Link to comment Share on other sites More sharing options...
OakenShield1 Posted August 9, 2011 Author Share Posted August 9, 2011 I was told by a turntable specialist that a thicker belt would solve the problem. It was initially 0.5mm thick which was slow. The new belt is 0.7mm thick which is still a bit slow but better. 0.9 should be enough to get it going at the correct speed. I would service the motor, but I'm scared of the cost of doing such a task. Getting a 0.9mm belt could be just a band aid as it slows down more and more. Or it could fix it and give me years of enjoyment. I figure I try the cheap option first Thanks for the great advice though If it comes to that, I'll be following what you say to the letter!! Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 9, 2011 Share Posted August 9, 2011 I was told by a turntable specialist that a thicker belt would solve the problem. Your "turntable specialist" is wrong. The motor requires re-lubrication. It was initially 0.5mm thick which was slow. The new belt is 0.7mm thick which is still a bit slow but better. 0.9 should be enough to get it going at the correct speed. Think about how belt drive turntables work: You have a very low torque, constant speed motor. A compliant torque coupling system (the belt). And a (almost) frictionless, but high inertia, platter. The platter is designed to operate with very little power input. Hence the use of a compliant coupling system and a very low torque motor. In fact, if the belt is too tight, you will find that the speed will be too low. If the belt is non-original, you may find that it has been fitted with a belt that is too small. Anyway, the upshot is, that I don't believe it. A thicker belt is very unlikely to solve your problem. I would service the motor, but I'm scared of the cost of doing such a task. Getting a 0.9mm belt could be just a band aid as it slows down more and more. Or it could fix it and give me years of enjoyment. I figure I try the cheap option first Kind of like looking for a lost coin under a street lamp, despite the fact that it was lost 100 Metres away. Anyway, sure, try it, but I still reckon your "turntable specialist" is wrong. The turntable is what(?), 30 odd years old? Trust me: The motor will require lubrication. Thanks for the great advice though If it comes to that, I'll be following what you say to the letter!! It is, indeed, highly likely that you will. Link to comment Share on other sites More sharing options...
VanArn Posted August 9, 2011 Share Posted August 9, 2011 Some turntable specialist! Zaphod is giving you good advice,You need to have the motor and platter shaft bearings cleaned and lubricated as a first step.This is a normal maintenance procedure and protects the moving parts from wear. To check if a belt requires replacement needs the following steps to be taken.Visual inspection for signs of deterioration such as hardening or a tacky feel. Cleaning,either by washing it in water solution with a little detergent added or wiping it with Shellite to remove grime.To test for a correctly fitted belt with the turntable running, hold the platter and see if the motor appreciably slows down or even just stalls.This indicates that the belt has sufficient grip to drive the platter.Too tight a belt also needs to be avoided as this will cause the motor to skew.The mounting springs and rubbers should also receive attention as these also can cause speed problems. Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 9, 2011 Share Posted August 9, 2011 Pre-zactly, VanArn. I've probably serviced well over a thousand turntables that are virtually identical to the JVC mentioned. I've probably even serviced a few JL-A1s. They all come in with the same types of faults. Dunno about you, but the quickest way to determine the need for motor lubrication, is to whack it on a Variac™ and back the Voltage (whilst running) down to around 90 Volts AC. If the motor drops it's guts at anything above around 120VAC, then it needs lubricating. I figured that trick out, back in 1976. It is almost 100% fool-proof. Belt quality, OTOH, is almost incidental. UNLESS the belt is too tight. As you know, a tight belt is the worst thing you can have on a belt drive TT. Link to comment Share on other sites More sharing options...
OakenShield1 Posted August 10, 2011 Author Share Posted August 10, 2011 I'm pretty confident it the motor was lubricated when I first took it to him about 8 months ago as the motor was making a slight noise, now it's quiet. I'll be sure to make contact with him today though and suggest some "Other" ideas at him rather than just getting a tighter belt. What you have said makes sense to me. IT was the right speed once, with the right belt - Something has happened to the motor since... Link to comment Share on other sites More sharing options...
Guest rondine Posted August 10, 2011 Share Posted August 10, 2011 A thicker belt will increase speed because of the greater increase in the effective diameter of the drive pulley compared to the driven platter. Not saying it will fix your problem though. ron Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 10, 2011 Share Posted August 10, 2011 I'm pretty confident it the motor was lubricated when I first took it to him about 8 months ago as the motor was making a slight noise, now it's quiet.I'll be sure to make contact with him today though and suggest some "Other" ideas at him rather than just getting a tighter belt. What you have said makes sense to me. IT was the right speed once, with the right belt - Something has happened to the motor since... As I previously stated, a loose belt will not affect the speed of a turntable, where the main bearing is in good nic (as long as it is not REALLY loose, of course). A tight belt, OTOH, WILL cause the TT to run slow. The motor is a low torque device and a compliant coupling is essential to correct operation. And, as I previously stated: Remove the belt and give the platter a spin. It should rotate freely and for many seconds. Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 10, 2011 Share Posted August 10, 2011 A thicker belt will increase speed because of the greater increase in the effective diameter of the drive pulley compared to the driven platter. No, it will do nothing of the sort, unless the old belt is REALLY bad. The thickness of the belt is not related to speed. The motor determines the speed. Not saying it will fix your problem though. ron There is very little chance that a belt change will help. The motor is likely to be at fault. (Is there an echo in here?) Link to comment Share on other sites More sharing options...
tal Posted August 10, 2011 Share Posted August 10, 2011 Agreed, thicker belts CAN change speed depending on your motor pulley, which is an unknown. I run an OL DC motor and use custom round belts. When I experiment with belt types and thicknesses I always have to reset the speed to suit. But then the OL pulley is radiussed. Thicker belts make the contact point of belt/pulley shift, increasing the effective diameter of the pulley as Ron said. But it looks like your are looking for a flat belt. So the pulley *probably* has a flat surface. If so the pulley diameter will not change and your belt change will be a waste of time. A cheap simple fix to speed things up would be to increase the pulley diameter somehow. But I'm not going there. Link to comment Share on other sites More sharing options...
OakenShield1 Posted August 10, 2011 Author Share Posted August 10, 2011 Alright, I need to find someone to service my motor I have asked him to remove the motor and I'll try and find someone to fix it up for me. Any suggestions? Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 10, 2011 Share Posted August 10, 2011 Alright, I need to find someone to service my motor I have asked him to remove the motor and I'll try and find someone to fix it up for me. Any suggestions? Any audio tech older than 50 should have no problems (because we've all done hundreds of them). In fact, anyone comfortable with relatively simple mechanical devices should be able to perform the task. Link to comment Share on other sites More sharing options...
Guest rondine Posted August 10, 2011 Share Posted August 10, 2011 No, it will do nothing of the sort, unless the old belt is REALLY bad. The thickness of the belt is not related to speed. The motor determines the speed. The thickness of the belt has to be taken into account because the linear speed of the outside of the belt is greater than the inside of the belt and the thicker the belt the greater this speed difference is. ron Link to comment Share on other sites More sharing options...
ozcal Posted August 10, 2011 Share Posted August 10, 2011 The thickness of the belt has to be taken into account because the linear speed of the outside of the belt is greater than the inside of the belt and the thicker the belt the greater this speed difference is.ron Yes . but it is only the inside of the belt that is in contact with the pulley and platter , so I can't see how the thickness of the belt would alter speed. Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 10, 2011 Share Posted August 10, 2011 Yes . but it is only the inside of the belt that is in contact with the pulley and platter , so I can't see how the thickness of the belt would alter speed. For a flat belt, it won't make any difference worth a damn. Round and square section belts are a different matter, since motor pulleys are often grooved to ensure correct running. A larger belt may not fit into the groove and the speed will be incorrect as a result. Link to comment Share on other sites More sharing options...
Guest rondine Posted August 10, 2011 Share Posted August 10, 2011 Well once the belt leaves the pulley inside and outside aren't going to travel at different speeds so it will travel along to the platter at a speed somewhere in between. If you take the average it means the effective (for the purpose of speed calculation) pulley and platter diameters are bigger by one belt thickness. ron Link to comment Share on other sites More sharing options...
Dustin Posted August 10, 2011 Share Posted August 10, 2011 (edited) Nah . . . I reckon the point is being missed. The motor pulley is in contact with (and drives) only the inside surface of a flat belt. Similarly, that same inside surface of the belt is in contact with the platter . . the driven 'pulley', if you will. It makes no difference if the belt is 0.7mm thick or 20mm thick because it's still only driving that same inside surface being driven. It is the motor that determines the speed of that inner belt surface. Of course a 20mm thick belt would undoubtedly bring other issues to the table, but for the sake of illustration, that'll do. Edited August 10, 2011 by Dustin Clarity Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 10, 2011 Share Posted August 10, 2011 Oh yeah, one more thing: Remove the platter and spin the motor pulley (with the power disconnected). The motor should spin freely. It it does not, then motor lubrication is definitely the problem. BTW: The motor MUST be dismantled to effect a proper repair. Just squirting oil into the motor bearings is not an adequate job. The motor must be stripped down, the old lubricant cleaned out and new lubricant (light oil, sewing machine oil is the correct stuff to use) added. Link to comment Share on other sites More sharing options...
OakenShield1 Posted August 11, 2011 Author Share Posted August 11, 2011 Ok Update, my bloke has had a good look at the motor and it seems to be running fine. He no longer thinks it's the motor itself, rather it's the pulley. Please explain to a novice, he seems to think it has a 60hz pulley on it and not the 50hz one it should have. He has lubricated the motor, reversed it (Turned it upside down or something) and it is running very strongly apparently, he reckons it's fine. He also said they can't be serviced as it's an AC motor or something. He doesn't think he needs it anyway. So what do I do about a 50hz pulley? Link to comment Share on other sites More sharing options...
Zaphod Beeblebrox Posted August 11, 2011 Share Posted August 11, 2011 Ok Update, my bloke has had a good look at the motor and it seems to be running fine.He no longer thinks it's the motor itself, rather it's the pulley. Please explain to a novice, he seems to think it has a 60hz pulley on it and not the 50hz one it should have. He has lubricated the motor, reversed it (Turned it upside down or something) and it is running very strongly apparently, he reckons it's fine. He also said they can't be serviced as it's an AC motor or something. He doesn't think he needs it anyway. So what do I do about a 50hz pulley? Sounds weird to me. For several reasons: * The motor can be serviced. The motor can be dismantled. And that is the only way it can be correctly lubricated. * IME, the best way to tell if the motor bearings are gummed up, is to spin the motor with no power on, or by using a Variac™ and adjust the Voltage down to around 100VAC. * Unless the TT has been imported into Australia from the US, or some other 60Hz country, it seems unlikely that the pulley is incorrect. Link to comment Share on other sites More sharing options...
wolster Posted August 11, 2011 Share Posted August 11, 2011 I wore a thicker belt once and I reckon I walked faster. Link to comment Share on other sites More sharing options...
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