# Help wanted with a Sony PS-33 (direct drive turntable)

#### john1

##### Active Member
Hi,

I'm trying to fix a direct drive tuntable unit, 45 and 33 rpm.
Its a Sony unit, PS-T33. Any help or advice would be welcome.

The speed control unit runs at 13 to 14 volts,
the motor appears to have windings in a square arrangement.

It has a speed sensor round the inner edge of the turntable,
which i guess is compared to the mains frequency,
but i dont really know.

The turntable doesnt rotate on its own, even if you help it manually.

but no explanation of how it operates.

Any help appreciated, John

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#### crutschow

##### Well-Known Member
Have you checked for power at the appropriate points?

For example here's the power input as taken from the schematic:

Look for about 10Vac voltage at the transformer outputs and +12.5Vdc and -13.5Vdc at the bridge outputs.

If you have that then just keep looking down the chain to see if all the other voltages look okay.

#### GromTag

##### Active Member
Not familiar with these models, Sanyo was the last I've been through and that was models from the 80's - early 90's, and some had strobo to control fine tuning of the selected motor speed. Still have a turn top for one.... somewhere.

If not an geared motor assembly then the turn top shaft may have frozen via lack of oil. The documentation shows the motor to be a magnetic type servo, the shaft can seize at the motor bearing at the square motor base plate if the record turn top disc itself is not in contact with the base (top deck) of the rest of the table (dragging) it can act quite like a brake boot when in contact. The PDF for documentation is 9.43Mb. So a link is provided if needed.

A link to the documentation is https://freeservicemanuals.info/en/servicemanuals/viewmanual/Sony/PST33/

The Type a PS-T33 is the acquirement of the datasheet. Year models under similar production model number may differ even with same number of PS-T33, use caution. Link to data provided if not known, and as you seem to have the components apart this could help with part identification and reassemble.

The PDF Zoom feature would be required to view the info in a readable sense. If a PDF viewer is available for the above overall.

#### KeepItSimpleStupid

##### Well-Known Member
It appears to be a complex beast. You do have a block diagram. As suggested, make sure the power supplies are working first. The neon light, the LEDS.

Then I'd concentrate on Ic-2 pin 5 and pin #6 and the C-E voltage across Q8. You don't want Q8 to be turned on.

What I don't like is the voltage ratings of C9 and C10. I think all sorts of failures are possible because of the lack of any clamping on the line voltage.

Your turntable has the strobe for the user to measure the speed, but the absolute speed is governed by the adjustments.

I worked on two pieces of instrumentation that have interesting case histories:

1) A thermocouple scanner that was used near a high power IR temperature controlled heater. The schematic showed the voltage regulator was unpopulated on the board. I chose the clamping fix.

2) A multi-channel analyzer which kept blowing $1000.00 USD boards. When i told the manufacturer that they had no surge suppression in their$5000 unit, they claimed they specify 120 VAC 60 Hz. Surges don't meet that requirement.

A piece of audio equipment was a repair return in a shop and I eventually got it to fix for the shop. An audio IC was tun too close to the maximum voltage so it kept popping.

#### john1

##### Active Member
Hi,

Yes, i know its been a while, but i'm still working on this thing
just a case of as and when.

Crutschow
---------
I will be double checking those voltages you mentioned, which i

GromTag
-------
No its not geared, its direct drive, the motor spindle is the
turntable spindle, and its not jammed or frozen, you can help it
turn by hand when its supposed to, but it doesnt even try to run.
Yet sometimes it gives a little jerk when its switched on,
so at least one of the windings is responding a bit.
Haven't got that link to work yet, still trying.

KeepItSimpleStupid
------------------
Yes it does seem overly complicated for a record turntable,
i will check out those connections on IC-2, and Q8.

I had not noticed how close C9 and C10 were up to the limit,
I will check them out too, and maybe up them to a bit of a
higher working voltage. I agree with you they should be a
little higher rated.

My regards to you all, and i will try to get this sorted.
Cheers, John.

#### john1

##### Active Member
Hi,

Yes its been a good while, but i am still pondering this thing.
It does seem to be a "Complicated beast".

I've checked the relevant supply voltages, C9 is (i think) at @ 13v
and C10 is (i think) at @ 13.5v

Why there should be a slight difference i dont know,
but it seems in keeping with the diagram, if a touch low.

Having had it apart further, i've found that the two motor coils
seem to be at about 60 degrees apart, not as i had thought at 90 deg.

I am wondering if the motor is driven by a sort of low Fr oscillator,
because the speed sensor seems to be reduced to a simple DC voltage.

I will probably have to get a scope running, to check it out.

Also i will check on the rotor, to see if it carries pole points,
which will have to be checked by feel when holding something ferric,
ive seen it, but poles wont show visibly so i will check that out.

I think 6 poles might make sense, with cycles sort of staggered
to the coils, i'm hoping someone on the boards has seen something
like this before, and give me some clue as to how it operates.

I will try to get back a bit sooner than before,
Regards, John

#### KeepItSimpleStupid

##### Well-Known Member
Just go ahead and replace those caps with 25 V rated ones. Without a scope you can't look at ripple. Long term you need to add some surge protection.

#### john1

##### Active Member
Hi,

You are correct of course, they are under-rated, and i intended to up them anyway.
So i will do that cos i have it apart again, if i have suitable ones, if not i will
order some.

The rotor has eight poles, not six as i had guessed.

I still cant get my head round how this thing is supposed to run,
i still think its going to be a low frequency oscillator, but i dont really know.

Someone else has had this to bits before me, which is always a worry cos you
dont know whats been tried or whats happened.

I will fire up my scope and have a look around the circuit.

Cheers, John

#### Nigel Goodwin

##### Super Moderator
I still cant get my head round how this thing is supposed to run,
It's a brushless DC motor, I agree though that it's difficult to understand how the circuit works - however, they have been extremely reliable, and I've only ever repaired a few over the years.

The speed sensor is compared with the setting of the speed controls (33 or 45, both adjustable) - this produces an error voltage, which is then fed to the motor drive section to change it's speed, IC1-2 looks to be smoothing the pulses from IC2 to give a nice DC level.

#### john1

##### Active Member
Hi Nigel,

Yes it is indeed brushless. It seems that transistors take the job that brushes
would do.

Motors ive seen before have mostly been sort of cylindrical, and have coils forming
a cylindrical space where the rotor fits in and spins.

This motor is not like that, the coils are on a plane, they form a flat surface.
The rotor is flat too, its a couple of cm. thick and circular, about 3.5" dia.
It has eight poles, i counted them.

Thing is, its direct drive, so for 33.3 RPM the drive a coil-pair would change
direction sixteen times for each revolution.
It would be pulling for a bit, then the pole would pass, and i guess it would
push for a bit, then i spose it would do the same for the next pole.

There are two coil-pairs, so i expect the other one to be doing the same as
the first. But half a pole out of step, so as to make it smooth.

Thats why i think its a "very low frequency" oscillator, a VLF.
But its not something i'm familiar with, so maybe its just switched DC,
like an ordinary motor, but with transistors instead of a commutator.

My little scope is playing up, soon as i get it running right i'll see if
its a VLF unit or not. If it is then its pretty slow, i reckon about four
cycles per second, roughly.

Its possible that the whole motor drive section is Ok, it doesnt drive til
the pick-up is over the turntable, so ive got to check that bit too.

Regards, John

#### Rusty116

##### New Member
Hi John,
I have just found your thread on the PS-T33 after lots of searching for help.
Did you ever solve the issues you were having?
I currently have 2 of the turntables, one powers up but the platter will not spin, i think it has the same issue as yours, the second which I bought as I was told it was working spins, but it seems slow to start and seems to be lacking in torque, and the wow and flutter varies and cannot be kept under control with the speed adjustment
Regards
Robert