How does the Sony Direct Drive BSL motor works / troubleshooting

[flavio81]

Hi,

This is useful information for troubleshooting the Sony motors: Understanding how they work.

First, it's important to say that the info here is NOT useful for the first-generation (1971) DD motors as found on the PS-2251 turntable. These motors work under a different principle.

It is also NOT good for the second-generation (-1976) Sony DD motors which say use the "saturable inductor". These are different motors.

The info is good for the third-generation Sony DD motors. These are readily recognizable by the two sets of coils in butterfly shape (see below) and the use of hall sensors. Also, all of them use the magnetic imprint on the platter for reading the actual platter speed (note that 2nd generation also use the magnetic readout too). A nice and interesting thing is that many Technics DD motors and some Hitachi motors use more or less the same system.

Pictured: Sony PS-T1 motor sans rotor nor spindle. Look at the sexy coils.

Examples of Sony DD turntables that use this third-generation system are: Sony PS-X50, PS-X70, really all Sony Ps-X series, PS-242, PS-11, PS-LX3 and others, even the tiny PS-Q7 uses the exact system. And others.

Sony PS-LX3 motor:

Now, how does this work? The Sony PS-11 manual has a great explanation. Please read carefully:



So, the rotor has many magnetic poles, as you can see, and there are two Hall sensors, H1 and H2.

The Hall Sensors are the little black (or blue) things next to the coils, and have 4 terminals: Two terminals receive a bias or control voltage, and the other terminals deliver a voltage that is proportional to the magnetic field. If the rotor spins, the magnetic field varies, and the output voltage will then be a waveform. If the control voltage is higher or lower, the output voltage amplitude will vary as well.

Let's continue with the text:





So, to make things simpler:

The two sets of coils require to receive sine waveforms with the correct phase relationship to make the motor rotate. The generation of these sine waveforms is made with the help of the hall sensors themselves, because when the poles of the rotor go through the hall sensor, the hall sensor generates a signal which is then amplified (Q10, Q11, IC1-4, etc) and fed to the coils. And this is how the rotor spins.

So the rotor spinning is what makes H1 and H2 (hall elements) produce sine waves at the out, and those sine waves, amplified, are delivered at the coils to make the rotor spin... It's a match made in heaven.




So how do we vary the speed? What makes it go faster or slower?

The PS-Q7 manual has a simple enough block diagram that will help us:



At the right we see L1 and L2, the motor coils. (On the picture they look like four coils but electrically they're two.)

How we see our friends H1 and H2, the hall sensors. And something called "DC Amp".

This "DC Amp" will give a control voltage that will decide the speed of the turntable. This voltage is what provides what I call a "control" voltage to each Hall element. "Gain" allows to do an adjust of this voltage, probably to compensate for Hall sensor differences or coil differences. The service manuals all explain how to set gain but it's obvious that we want the output from the hall sensors to have pretty similar waveform amplitude and we can use "Gain" to achieve that.

We can also assume that too much gain could fry the hall sensors...

Now, the output from the hall sensors go through an amplifier made with an opamp and two transistors, and this amplifier directly drive the coil. What's the "offset" control?

Again, getting back to the PS-Q7:




We can see that the "Offset" control will allow us to tweak until we get a symetricall waveform to the coils.

PS-X50 manual:



What is the manual asking us to do? What's "disconnect the white wire and connect the regulated power supply"? In essence, what we're doing is disconnecting the control voltage from the DC amp (see prior diagram) so we can supply our own, fixed, control voltage.

Then we need to check that the output waveform, the one that would go to the coils, is symmetrical. This can be done with an oscilloscope (you really need an oscilloscope if you want to troubleshoot most DD turntables), or by assembling the circuit on the picture and checking that the out is 0 AC volts with a VTVM or digital multimeter sensitive enough. What this circuit does is rectify the positive side and the negative side, smooth it, and substract one with the other; ideally the out should be 0 volts.

So that would be the offset adjustment and the gain adjustment.

Now, what's the magnetic imprint on the platter for? And the magnetic readout head? Those are for controlling the speed circuitry that ultimately produce the control voltage that appears after the "DC amp". And the control method would differ if the turntable is quartz-locked or not. Most QL turntables use the CX-193 Sony IC for the control. But all of them have the magnetic head.

This head reads the magnetic imprint on the platter rim and should produce a periodic output waveform. For example on the PS-X50 and similar TTs this would be a waveform of 284Hz (see image) and a magnetic head output voltage of 30mV or more.



Now, how can we troubleshoot? How do we proceed? I will explore on the next post.

 

[flavio81]

So, how do we troubleshoot?

I'm far from an expert on these TTs (still, I want to offer help), but my advice would be the following:

1st: The power supply. Since the power supply delivers the voltage that is (almost) directly applied to the hall elements, and the voltage that is used to amplify the voltage to the coils, and the voltage that powers the "DC amp", and the like.. the TT needs stable, smooth power supply, otherwise nothing will work as it should. So you first need to ensure the power supply isn't doing crazy things and the voltages are what the TT needs. I have next to me a PS-X50 whose power supply is doing crazy things, the strobo lamp flickers and the control circuitry goes crazy. Just some days ago everything was stable! So normal troubleshooting of power supply should come first.

2nd: Now we need to ensure the hall sensors are working fine. Make sure there is some voltage entering the hall sensor (on this diagram it would be the voltage entering to the left side of H1 and H2). This is the voltage controlled by the GAIN potentiometers, which you won't touch or alter needlessly.

If the turntable spins, use an oscilloscope (no excuses, get a damn oscilloscope even a cheap chinese portable toy one) to check that the H1 and H2 hall elements are really outputting a waveform of healthy voltage. If you can't get the TT to spin, spin it with your hand.

On a TT i'm currently working on, one Hall sensor is apparently dead, and outputs just some millivolts while the other Hall sensor outputs in the magnitude of a few volts peak-to-peak. Of course the actual amplitude would depend on the control voltage from the "DC amp" so you can always do what the service manual says: disconnect the DC amp from the hall sensors so you can inject your own control voltage... if you don't have a controllable voltage source, even a 1.5v battery could be useful for this.

A dead or faulty Hall sensor would mean jerky rotation (which might be invisible on the stroboscope!) strange noises from the motor, or even very jerky rotation and the motor failing to start from certain platter angles.

Back to the PS-Q7 schematic:


So if you are getting an output from the Hall elements the next thing to do is to check if the transistors (Q111, 112, 113, 114) on this diagram and the IC (uPC4558C) are fine. As you can see the IC is a common run of the mill opamp so you can even replace it, it costs nothing. The transistors can have had a rough life so they should be checked. All in all, a healthy voltage should go to the coils. On the PS-Q7, which has a tiny motor, it says 3 volts peak-to-peak at 33RPM.

By now you should have already found something not working correctly. But if you haven't, and the motor still has problems, now we can look at the control circuitry, the one that produces the DC voltage.

I don't have a good write-up for the control circuitry, because I haven't found control circuitry problems yet, but first you need to address the obvious: Dirty/faulty speed control switches and potentiometers!! They are more common than you would think!

Second, what I would do is first to confirm that we're getting a voltage from the magnetic head and that the signal appears healthy without interruptions, which would mean the magnetic track was damaged. (Use an ... oscilloscope.)

Then if i don't find nothing strange yet the DC amp doesn't get a correct control voltage, i would try regular troubleshooting and normal measures such as resoldering every solder point (to correct potential cold solder joints), checking that the potentiometers are working OK, maybe taking a look to electrolytic capacitors. Basic electric stuff first need to be adressed, ICs should be the last thing you should blame.

I hope this info is useful!!

 

[flavio81]

Now for some fun and didactical purposes...

Technics SL- D202 motor. You can see the hall elements. As far as i can remember it uses two star-shaped coils in 22.5° arrangement, just like the Hitachi uni-torque. Similar to the Sony in principle, different execution (different coil shape, for example). The serpentine-shape PCB track on the outside is used for measuring the speed of rotation.

Note that not all technics DD motors are like this, the first-generation DD technics motors are different; the SL-1100, SL-1200MK1, MK2, SL-10, SL-1500/1600/1700 and others use a diferent kind of motor that uses no hall sensors (they use coils instead of hall sensors).





Sharp Optonica RP-7100 coils... do you see something familiar? Yes, the coils are in a different arrangement but the principle should be the same.

 

[cnolanh]

Really appreciate this careful, detailed info on troubleshooting and fixing these Sony beauties! I have a PS-X70 which I love. It’s in a local shop for service right now because I don’t have all the tools and expertise to dig into it (auto-return is inop but the rest of the table works well).

 

[flavio81]

Really appreciate this careful, detailed info on troubleshooting and fixing these Sony beauties! I have a PS-X70 which I love. It’s in a local shop for service right now because I don’t have all the tools and expertise to dig into it (auto-return is inop but the rest of the table works well).

Let's pray that the technician doesn't mess at all with the "SPEED", "OFFSET", and "GAIN" adjustment knobs!!

Indeed those are beauties, Sony did some very nice TTs, my love started with PS-2251.

 

[cnolanh]

Let's pray that the technician doesn't mess at all with the "SPEED", "OFFSET", and "GAIN" adjustment knobs!!

Hope so! They have worked on this series before and they even have a PS-X70 parts table, so I’m hopeful. They’ve repaired several other pieces of equipment to my satisfaction, though this might be the most complex beast I’ve brought them.

 

[Pio1980]

Hi Flavio!
Most of the Japanese coreless planar spindle motors are similar, the German 701/721 Dual DD planar motors are quite different tho the operating principle is similar.

 

[Sam Cogley]

So, how do we troubleshoot?

I'm far from an expert on these TTs (still, I want to offer help), but my advice would be the following:

1st: The power supply. Since the power supply delivers the voltage that is (almost) directly applied to the hall elements, and the voltage that is used to amplify the voltage to the coils, and the voltage that powers the "DC amp", and the like.. the TT needs stable, smooth power supply, otherwise nothing will work as it should. So you first need to ensure the power supply isn't doing crazy things and the voltages are what the TT needs. I have next to me a PS-X50 whose power supply is doing crazy things, the strobo lamp flickers and the control circuitry goes crazy. Just some days ago everything was stable! So normal troubleshooting of power supply should come first.

Great stuff here on troubleshooting these tables!

I've been harping on it for years, but your point #1 is absolutely the foundation of getting any DD to work right. Most of them are extremely sensitive to power supply issues, to the point where sometimes components which test OK out of circuit won't pass muster in operation. Fix the power supply first, make sure it's dead on, then start on anything else that's misbehaving.

 

[flavio81]

FYI - "BSL" means "Brushless and Slotless"

 

[Pio1980]

I still have a PS-X70 for back-up I can't yet bear to pass on. It was a big bang for bux TT back in the day with a very good PUA-7 arm, the drag-y AS notwithstanding. The arm bearings are superb.

 

[flavio81]

Just a simple addenda for troubleshooting.

Power supply unsteadiness/ripple/variation will directly impact (among MANY other things) Hall element "gain" voltage and this will directly change driving coils' power (voltage amplitude) which if not properly compensated by the speed control circuit will also result on unsteady rotation of all sorts.

A faulty power transistor, and more particularly one of the 4 that drive the motor coils proportionally to Hall output, will cause a lot of problems. These 4 transistors are almost always directly connected to power supply rails, so shorted or faulty transistors will directly break havoc with two of the supply rails and cause all, all sorts of trouble. (*)

Thus, when diagnosing the power supply I would suggest removing the coil driving power transistors, or (even better) decoupling the power supply rails from the rest of the circuit, which is simple on some TTs but on other Sony TTs the power board and drive board are the same.

(*) if you test the output voltage at the output of the motor drive transistors, you won't be able to discern whether the power transistors are faulty, the opamp IC that drives the transistors are faulty, or the Hall elements are faulty.

 

[Beobloke]

Just to add, on the Sony PS-X9, a failed Hall sensor causes the motor drive circuitry for that section of the motor to ramp up to full power.

The drive circuit for this unit has lots of power to give, so the end result is blown drive transistors and flames from the PCB.

I’ll give you three guesses how I know this!

 

[flavio81]

Just to add, on the Sony PS-X9, a failed Hall sensor causes the motor drive circuitry for that section of the motor to ramp up to full power.

The drive circuit for this unit has lots of power to give, so the end result is blown drive transistors and flames from the PCB.

I’ll give you three guesses how I know this!

Thanks for this info. This would mean -i guess- that a failure mode of the Hall sensor is to fully conduct.

Which would then make the opamp after the sensor (probably a uPC4557) apply full power to the drive transistors.

And start the fireworks.

 

[Mi Li]

The best Linear TT known to me

https://www.whathifi.com/reviews/holbo-mkii-airbearing

 

[Pio1980]

The best Linear TT known to me

https://www.whathifi.com/reviews/holbo-mkii-airbearing

Offhand I'd say the Versa.

 

[zaskarx]

I have a Sony PS-X50, I'm working through the gain and offset procedures. I have an analog scope (and a DMM that doesn't seem to be of much use) but am finding that the sweep speed is so slow that I'm not getting persistent waveform to measure. Instead, the waveform looks like a fast bouncing ball that is very tricky to measure. I think I'm close, but wondering if there is a better, more precise way to make these measurements? Am I doing something wrong with my scope settings? Thanks.

 

[flavio81]

I have a Sony PS-X50, I'm working through the gain and offset procedures. I have an analog scope (and a DMM that doesn't seem to be of much use) but am finding that the sweep speed is so slow that I'm not getting persistent waveform to measure. Instead, the waveform looks like a fast bouncing ball that is very tricky to measure. I think I'm close, but wondering if there is a better, more precise way to make these measurements? Am I doing something wrong with my scope settings? Thanks.

You need to specify which signals are you trying to measure.

 

[zaskarx]

Thanks for getting back to me, I'm measuring the Hall Device Gain and Motor Amp Offset (SM pictures attached), using an analog scope for both since I don't have a VTVM. I have a regulated DC power supply hooked up and providing 1.5V and am attempting to measure 1.9V peak to peak for the gain and "A=B" for the positive and negative parts of the offset signal. I can provide pictures of what I am seeing on the scope if that is helpful.

 

[flavio81]

that the sweep speed is so slow that I'm not getting persistent waveform to measure. Instead, the waveform looks like a fast bouncing ball that is very tricky to measure.

Please take this in good spirit because It's not my intention to be offensive, but, do you know how to set trigger level on your oscilloscope?

As long as you see the waveform (even as a "bouncing ball") you should be able to stabilize it by changing the trigger level/trigger configuration. And afterwards, you just change the timebase (the sweep frequency) so it looks nice on your screen. (You can also do it the other way around, first set sweep frequency to something acceptable, and then stabilize the waveform using the trigger)

 

[Pio1980]

If I could find someone local trustworthy to overhaul the electronix in my PS-X70, I could be satisfied with it as my main TT, tho it is functional.