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Mitsubishi LT-5V

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Mitsubishi LT-5V

Postby DigitizerGuy » 02 Feb 2011 01:19

Hello - I'm brand new to this site. I came here as I just unpacked my Mitsubishi LT-5V after 5+ years of storage. It was working properly when packed up. I wanted to apply a vinyl/rubber preservative to the belts (I replaced all three of them just before I packed up the turntable 5 years ago). I'm now setting up my system again and wanted to set up the turntable. I seem to have at least 2 problems. The first is that the motor doesn't seem to have enough torque to start. I can get the platter rotating if I start it and manually rotate the platter but it won't start on its own. I think the lubricant is probably old and needs replacement. The problem is not that the belt is slipping - I felt the motor pully and the motor is simply not turning. The second issue is that it seems like the turntable operation is not properly synchronized. I think that I probably caused this problem by rotating the arm lift and tracking mechanisms by hand in order to apply the preservative to the belts. I think that I got the cams out of synch with the actual state of the turntable and now the platter motor run (after the manual push) with no record present but will not run (even if manually assisted) if there is a record present on the turntable. So my question is: Does anybody know how to reset the cams so that the turntable runs with a record present? Is there a procedure to reset the state of the turntable? Also (and I'm not sure if this is a problem or if it is supposed to operate this way) with no record on the platter and the platter running, pressing the repeat button sends the tonearm motor seeking back and forth across the turntable (with the arm cued up) in an endless loop. This may be because there is no record present or another problem with the states of the mechanisms not being correct. I downloaded the service manual and read it, but it doesn't seem to have any information regarding the synch issue although it does state that lubricating the motor is not necessary and can cause problems. Any information or help would be greatlyappreciated.

Thanks in advance for any help.
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Postby lensmanMK2 » 02 Feb 2011 19:30

the lt5v doesnt work on a mechanical system in order to work, its all IC/optically controlled, so you cant really put things out of sync, more than likely something electronics gone on it, 3 IC's on the board are unobtainium but the rest are replaceable simple transistors


lube wise ignore what the instructions say, you can (and should) lube up the main bearing and motor, i did a post on it a few weeks ago, just do a search

but if the motors gone your probably screwed.. the motor on mine has just given up the ghost and im trying to track down a suitable replacement, but mitsubishi stopped making this motor type about 20 years back, and not many people seem to know about dc pll motors.
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Problem Identified, Fix On The Way

Postby DigitizerGuy » 08 Feb 2011 02:07

LensmanMK2 - Thanks for your reply and the information in it. I downloaded the service manual for the turntable and found a reasonably good schematic for the electronics. Tracing the signals for the platter motor resulted in finding that the control signal to and from the motor seemed to come and go. I had an idea for making a motor tester out of a 9V battery and a 27K resistor soldered to a mating connector for Connector 6 on the cable from the control electronics to the motor. Using this, the motor ran fine. By changing resistor values, I could verify that it ran at the correct speeds. So then I started tracing the signals to and from the control logic. All looked correct. Then at one point when the turntable should have been running but wasn't, I put my "needle" probe into the "C" signal in Connector 6 and the motor started. I think that over time the spring tension in the Molex connector has relaxed and the contact is intermittent at best and putting the probe in the wire side of the connector made the pins make contact. So all is well now (at least it will be when I replace the connector). Thanks again for your help and perhaps this information might help somebody else at some point.
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Postby lensmanMK2 » 08 Feb 2011 19:45

well you better with electronics than me :) i can just about recap and test/replace ic's/transistors.

so with this motor, PLL is internal? having a look at the schematics i thought it worked on a pll pulse system from one of those daft custom ICs!

so.. any idea what type of motor i could use to replace the mitsi one, ie would i need one with internal PLL or could i use something easier to get hold of?

oh and what does Vr and C signify on the motor inputs on the schematic?

appreciate the help!

(and lube that bearing up :) lithium moly grease sounds the best, and should last for years!)

edit: just re-read properly (on a mobile phone at the moment :) ) C is the control wire, and that also regs the speed.. so any idea what that Vr one does? i'll try your method when i get home to see if the motor spings into life, still would be good if we could bang our head together and find a "superior" motor to these old mitsi ones that are pin compatible
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Postby DigitizerGuy » 09 Feb 2011 17:01

LensmanMK2 - Sure, I'd be happy to help try to debug your turntable. I have a doctor's appointment this morning, so I probably won't get a note off to you until late this afternoon (I started one a few minutes ago and realized that I'm going to to have to take more time in describing things than I had first thought). I'm new to this forum and I don't see a way to attach a file on the forum but if there is, that would be helpful as my description might get more detailed than is appropriate on this forum. I'll finish the first description I started this morning later today.
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Postby lensmanMK2 » 09 Feb 2011 17:40

appreciate the help :)

well, tried the 9v 27k resistor trick last night.. no go so it does look like the motor is fried..

attachment wise you could always use sendspace.com, speeds are very good and you dont need to register.
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Postby DigitizerGuy » 10 Feb 2011 00:57

OK, at this point things get complicated. To find a suitable replacement motor is a complex question. There are issues of RPM range, no-load speed, starting torque, input voltage, control electronics method, bearing type, physical size, mounting method, etc. to consider. I did some searching on the net and so far came up with only 1 motor that might be suitable (I'm not sure as there are some things I'm not very knowledgeable about, so this is only a guess at this point) and because of its length it may not be physically compatible. Anyway, to address some of the questions, I measured the diameter of the driven flywheel on the back of the turntable to be 7 1/16 in and the diameter of the pulley to be 0.181 in. This implies that for a 33 1/3 LP the RPM of the motor is ~1300 RPM and for a 45 RPM record the RPM of the motor is ~1756 RPM. I measured the diameter and length of the motor both to be approximately 1 1/2 in. The pulley extends to ~2 1/4 in. I didn't take the pulley off the shaft so I don't know the diameter of the shaft, but since it would be desirable to use the same pulley, the output shaft of the motor should match it. In order to simplify mounting, it would be nice if a motor whose length and shaft extension made it possible to line up the pulley with the flywheel so the belt drives the flywheel properly. The voltage supplied to the motor by the board is approximately 11.4 V although this can vary by a little bit either way. I haven't tried to calculate the necessary torque yet as this is getting a little complicated. So before I get too far along, let me just review your results so far. When you say that the battery/resistor test didn't work, I'm assuming that you disconnected Connector 6 from the PC board (this is the cable from the platter motor to the PC board - 4 wires: red, black, gray, white). To the connector on this cable you connected the 9 volt battery with the negative end going to the black wire, the positive end going to the red wire and the resistor going from the white wire to the gray wire. I'm also assuming that these connections were electrically sound because any one of these not making good contact would result in the motor not working. Also, if you did as I did and used a Molex header to plug into the connector, it is important that none of the wires touch as the pins are on 0.100 in. centers and are easily shorted. The reason I'm stressing this is that I had a bit of difficulty getting things connected firmly to test the motor myself. If my assumptions are correct, then I would agree that the motor is the problem. If that is the case, then it could be possible (but probably a bit expensive) to have it repaired. I found a company in Canada (http://www.servo-repair.com) that says they can repair small motors of this type. There may be similar companies in the UK although I'm pretty certain that any such company no matter where they are located will be somewhat pricey as the time involved would probably be at least an hour. However, as I said, finding a suitable replacement and adapting it to the LT-5V could end up being a very large time investment. From my initial investigations, I doubt that a plug-in replacement exists. To adapt another motor to this application could take both electrical design and mechanical fabrication. So, let me know if my assumptions about your testing are correct and how you might want to proceed.
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Postby lensmanMK2 » 11 Feb 2011 02:40

thanks for all your help so far digi

i had connected it a bit different with just the 9v and resistor in series to the C terminal, so i rewired it the above way..still no go. there is power getting to the motor at V11.20 bit lower than what you found but i think it should still turn as its only a minor voltage drop

anyway i had a look at motors myself, adapting it mechanically wont be much of a prob for me,electrically.. well thats another matter :)

i was thinking about drilling a hole out the back of the case and mounting the motor on that with a bracket (so the motor is facing towards the front of the deck rather than the rear)

im wondering if this motor could work:

http://www.kraftronic.com/webshop/produ ... 7o9qf70vv2

a guy on the diyaudio boards states this had internal PLL.. but i cant find any pinouts


but to be honest id rather replace the motor with something a bit easier to get hold of and possibly superior to the existing mitsi unit, maybe something by maxon or another big motor company, trouble is i just dont know enough about the control electronics of motors :)


as per the general motor specs, a sleeve bearing might be better than a ball bearing one as the race might rumble a bit, and maybe brushless? but from what ive read the control circuitry is different for brush/brushless so all depends whats in the Lt5v at the moment i suppose
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Postby DigitizerGuy » 11 Feb 2011 04:56

Hi - Sorry to hear that the motor seems to be DOA. I looked at the Kraftronic motor but there is precious little information regarding specs/diagrams, etc. (at least that I could find). I did some searching and did find some posts about the modification of a motor as a turntable motor (1170.2 RFT). It appears that there was a kit offered by Scheu Analog which included the motor modified for use with a turntable. However when I actually went to the site I couldn't find the kit. Since the post describing it is about 5 years old, it may not be available anymore. Here is a link to the description:

http://translate.google.com/translate?h ... rmd%3Divns

I hadn't considered the possibility of modifying the back enclosure to allow a larger motor to be installed so if you are willing to do that, some additional motors become possible. Certainly your thoughts on sleeve vs ball bearings and brushless motors are valid. Ball bearings would create some degree of rumble although it would be greatly attenuated by the belt drive. However, starting with a lower level of rumble in the first place would obviously result in less rumble transmitted to the platter.

My analysis of the Mitsubishi electronics is that if a suitable motor can be found with some method of feedback speed control (PLL or otherwise) as a sort of standalone unit, that is really all that is necessary. The only functions that the Mitsubishi electronics provide to the platter motor are:

1. Application of power - this comes from the T/T (Turntable?) signal on IC102 (pin17) through transistors Q127 and Q128 to the + terminal of the motor. In this case Q127 is acting as a switch - either off or connecting the motor to +11.5 volts (minus about 0.1 v across the collector/emitter terminals of the transistor when on).

2. Speed selection of the motor which is done by the Speed output of IC102 (Pin 16) turning on one or the other pair of switches in IC105 to alter the resistive feedback loop. The 33 1/3 speed has an additional 13K resistor (R151)added to the 5K variable resistor (VR103) used to fine tune the speed using the stroboscope. The 45 speed only uses a 5K variable resistor (VR104) although there is also a 10K variable resistor (VR105) common to both speeds which is set at the factory to adjust the speed to be within the adjustment range of the 5K variable resistors.

Anyway, if a motor can be found with its own speed control, then either a manual switch to apply power to it or a relay to allow the T/T signal to apply power to the motor via the relay is all that is needed. The new motor must have some means of changing the speed. Again, if this could be done with a manual switch, then it is also possible to use a relay driven by the Speed signal to automatically change from one speed to the other. If it is desired to use the stroboscope to fine tune the speed, then the motor's speed control would have to have some form of manual adjustment so that you could watch the strobe and adjust the speed.
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Postby DigitizerGuy » 11 Feb 2011 15:29

LensmanMK2 - I was searching on the Kraftronic website and discovered that it appears that the motor referred to in the description linked in my previous post (1170.2 RFT) may also be available from Kraftronic (7 EU). There is a motor listed as Motor SK3000 1120.7-2 5,5V Tonwellenmotor [90200002] on their site. I'm not sure if it is the same one as the RFT suffix is not present and I could not find any specifications for it. I assume it is a 5.5 volt DC motor but I don't know if it is the same one as described in the link in my previous post. I did request specifications on both this motor and the one you referenced but have not received a reply (also, since I don't speak German, they may be undecipherable if I do receive them). You can view this motor at this link:

http://www.kraftronic.com/webshop/produ ... ts_id=2012

I'll let you know if I hear from Kraftronic.
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Postby lensmanMK2 » 12 Feb 2011 00:20

good find digi

i dont think you'll have a problem with replies, if this guy is running an electronics store no doubt he'll speak english

the voltage is a bit lower than the one shown on krishnus site (9V) but like you said a relay could be used on the LT5v 11.4v to switch it on, and im sure theres 5v somewhere on the board i could tap into, but all depends on the torque of the motor,as you know how heavy the lt5v platter +flywheel are

main problem now is getting a spec sheet to find what gets wired to where on the motor,i thought about checking the resistances of the windings, but again, without the specs i could just be measuring the resistance in the control circuit..

having a look around at new motors it seems most need a pretty complex (and expensive) servo amp/circuitry in order to finely regulate speed, none seem to have internal PLL

i wonder why they stopped making dc motors with internal pll?
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Postby DigitizerGuy » 12 Feb 2011 21:12

Yes, I've noticed a distinct lack of internal PLL motors too. Today I started doing a little thinking into the implementation of a PLL control circuit to control a DC motor. This was partly because the picture of the motor to which I linked yesterday morning looks like it might only have 2 wires connected to it rather than 4 as would be expected for a feedback controlled motor. I'm not positive on this as the picture is not too clear in showing the external wires. The motor that Krishnu used clearly was a feedback controlled motor but it could be that this one is not exactly the same model and is not controlled by feedback (I'm still wondering about the RFT suffix in the part number in Krishnu's description). So anyway, I started thinking about ways to provide an external PLL and control the voltage to the motor which in turn would set the speed. A key requirement is a phase signal to compare to a fixed, stable oscillator. There is nothing all that magic about a PLL. It is simply a way to implement a feedback system to control an oscillator. In this case the oscillator is actually the motor. The thought occurs to me that a way to obtain the signal representing the phase of the motor could be to create what is commonly called an "encoder wheel." A relatively simple way to do this would be to use a CAD program to draw a circle of diameter 1-3" or so with several diameter lines on it (making it look like spokes on a bicycle wheel). By filling in alternating segments with solid black, a pattern of alternating black/white can be created. I did a sample using TurboCad and it looks suitable. Unfortunately, I can't seem to embed the image in this post so you can't see it. The reason for the CAD program is to draw the diameters very accurately. Then, if this was printed on a transparency and cut to size, then glued to a clear plastic circle to provide rigidity, this could be glued or screwed to the end of the pulley and an LED/photodiode optical sensor (a common component) could be mounted so that the black segments interrupt the light beam from the LED and create the speed/phase signal to a PLL. Alternatively, the transparency disk could be sandwiched between 2 smaller diameter plastic or aluminum disks (the lighter the better so as not to load the motor excessively) so that the outside portion of the segments would extend beyond them and this whole assembly mounted on the motor pulley. A consideration about this construction is to make sure that it is mounted so that the center of the encoder wheel is accurately placed at the center of the pulley (and, by extension, the motor shaft). If the axis of rotation is off, it will result in "flutter" in the phase signal and thus the motor speed (although this would be small as the combination of the electrical parameters of the motor, the PLL loop filter bandwidth, the inertia of the heavy flywheel/platter, and the coupling of the motor to the flywheel/platter via the belt would probably render it so small as to be negligible). However, any off-center mounting would contribute to unbalanced loading of the shaft and bearing and consequent vibration and wear. Anyway, I'm still thinking about what would be entailed in a project such as this. There are a number of things to consider like lock range, steady-state error, jitter, noise, motor parameters, speed adjustment mechanism, testing and verification, etc., not to mention the layout and fabrication of a PC board to house it. I don't know what resources are at your disposal to execute the mechanical and electrical aspects of doing this if a suitable feedback motor cannot be obtained so this may be just a mental exercise. I can perhaps provide advice on how to approach this if you either can, or know somebody who can, do the detailed PLL implementation and testing and circuit board fabrication. I'm still waiting on a reply from Kraftonic but as I sent my request after working hours in Germany on Friday, I don't expect anything before Monday. Depending on the motor characteristics, the whole PLL issue may disappear.
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Postby lensmanMK2 » 12 Feb 2011 21:53

very thorough job digi! are you an electronics engineer for a living?

and to answer your question: the mechanics of putting everything together wont be much of a problem, i have access to a lathe so i could make the pulley for the motor,and a mounting bracket with resonators etc,and id be happy to sort a bracket and pulley for you incase your motor decides to commit harakiri in the future.

the electronic design part.. well,definelty not my strong point

anyway..

motor wise, encoders seem easy to get hold of, most of the main manufacturers spec them on their range

i did find this site though:

http://www.sansui-parts-shop.com/index. ... 0&group=68

that motor looks like a PWM control im guessing (cant see an oscilator) but it has the 4 pins possibly for power + control and ground, im on the verge of getting way out my depth here


another option would be this place:

http://www.diyhifisupply.com/catalog/29

they sell both a motor and board for diy ($40 for a pcb though!) the motor is a premotec cl27 and the torque is very low, not enough to drive the mitsi id guess

but weather the circuit board could be adapted to a larger torque motor (ie the premotec cl40) i dont know, so i'll drop them a mail and see
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Postby DigitizerGuy » 13 Feb 2011 03:00

Guilty on the electronics engineer charge. At least I was until I retired a few years ago. I still dabble a bit and consult with former colleagues on occasional hobby questions. When I was working and had access to a lab with all the necessary equipment, this wouldn't have been as complex a task as it appears now.

I spent some time looking at the site where you found the motor you referenced. I also found a site where a lot of Sansui turntables were listed with some (usually not much) information about a lot of them. Here is a link:

http://www.akdatabase.com/Sansui/Report1.pdf

The PE 350 from which the motor to which you linked came is listed as a linear tracking (like the LT-5V) automatic turntable from 1970. This makes me wonder a couple of things.

1. Since this is a linear tracker, is this the motor for the platter or for the arm tracking mechanism?

2. At that time, direct drive turntables were very popular. If this is the platter motor from a direct drive turntable, the motor would be geared down to the 33 1/3 and 45 rpm speeds which would make using it for a belt drive system difficult at best.

I tried to register on the Sansui-Parts site so I could question them about any information of this and other motors but I can't seem to log on (even after having them send my login information back to me in case I misspelled something). I sent them a request to get some help on this but it probably won't be answered until Monday.

I also found the following site which has factory brochures for a lot (not all) of Sansui turntables which provides some information about them.

http://www.classicsansui.net/images/Lit ... 2mk5_1.jpg

From this I found that the SR 222 MKV turntable was a belt drive servo system (like the LT-5V) so this is one for which I would definitely like to obtain spec's and wiring diagrams. If I can ever log onto the Sansui-Parts site, I will ask for them. This motor is also available on the Sansui-Parts site for 10 EU.

http://www.sansui-parts-shop.com/index. ... 0&group=68

I also went through quite a few of the motors listed on the Sansui-Parts site. Some were synchronous AC motors (not applicable to your purpose), many were for direct drive turntables (again not applicable) and some clearly had only 2 wires (not servo motors and would require external control electronics). I'm still looking at these motors as I'm not done yet.

I looked at the diyhifisupply site. It appears that they sell parts that can be used to build a turntable. Presumably these are all compatible but I'm not sure on this. I tried to find information regarding the motor (Prima Tech) I found a site in the UK (conveniently) where a motor with the same part number seems to be available. I'm not sure if it is the same motor or not but even if it isn't, it might be applicable as it is a DC servo motor of the same size and with a speed range that might be appropriate. Here is a link to their site (McClennan).

http://www.mclennan.co.uk/datasheets/eu ... motors.pdf

The physical size of the Prima Tech motor is almost the same as the LT-5V motor. I'm not sure about the electronics and how they are connected (I'm assuming that the electronic controller is for this motor). The downside of this is that by the time the motor and electronics are purchased the price tag is getting pretty steep (~100 EU). The upside is that it appears that it would be pretty much plug and play (with the possibility of needing to fabricate a bracket, perhaps making a custom pulley if their turntable drive flywheel is much different than the LT-5V flywheel in diameter which would take it out of the adjustment range, and purchasing their power supply as the current available from the LT-5V may not be 2 amps like their power supply provides).
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Postby DigitizerGuy » 15 Feb 2011 23:55

LensmanMK2 - I was able to contact the Sansui-Parts site, but they had no information about any of the motors so that seems to be a dead end. I haven't heard from Kraftronic. I sent some questions to DIYHiFiSupply but haven't heard back from them.
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