Numark TT-1

[bigfathairyvika]

Hi All,

I have a Numark TT-1 record deck here pulsing the motor, so not getting up to speed.

I have searched high and low for a schematic, but only found scam sites.
I have checked electrotanya etc.

Anyone know if these units get failed motors or is it usually the driver chip?

Thanks,

Mark

[stacman]

These are also branded ION turntables, I have an ION TTUSB 10, also search for ION iTT, pretty all similar, the difference is the Numark ones have an alloy platter as opposed to the plastic platter of ION ones,
12voltvids on YouTube has done a repair/tear down of an ION one that may give a few clues.
Regards,Alan.
https://m.youtube.com/watch?v=Ia_LlrM8iDQ

[McMurdo]

are you trying it with the platter in place? These will pulse the motor if no platter is mounted

[bigfathairyvika]

Originally Posted by McMurdo

are you trying it with the platter in place? These will pulse the motor if no platter is mounted

Platter in place , it rotates but slow pulsing rotation.
Platter not mounted and it pulses fwd and rev so no actual rotation.

I have now found a TT200 schematic which covers the motor drive ( minus the Xilinx chip board ).
I'm just about to probe the motor feedback pulse with a scope....

Mark

[bigfathairyvika]

Well how about that!

Deck upside down , about to probe , press start button, platter spins up.
Turn deck right way up and motor fault returns, platter slows down.

Well, I'm getting somewhere.....

Mark

[Edward Huggins]

Wow, on seeing that Video embedded in #2, I never realised that these very cheap and cheerful plasticy turntables contained so much electronics!
I had one once, but I felt rather ashamed of it and gave it to a Charity Shop - but I never even bothered to even take a peek inside.

[bigfathairyvika]

Checked out the ION video and it appears that the ION turntables are cheap belt drive motor units.
The Numark decks are direct drive motors with speed feedback.
Still, the tone arm mechanics are pretty rubbish on the Numark.

[bigfathairyvika]

Ok, upside down, platter rotates , but no speed control.
Basically spins up over 100 rpm. Bit fast even for a 78.
Obviously, when upside down, the magnets aren't near enough to give good enough output from hall sensors.

[julie_m]

That's ..... not quite how these things work.

A brushless motor works on the same principle as any DC motor -- keep changing the magnetic field so the armature will always be attracted from somewhere up ahead of itself in the desired direction of rotation, and repelled from the pole it has just passed. But instead of a commutator and brushes, it uses transistors to switch the current in the windings, and uses a Hall effect sensor to determine where the magnet is.

A computer power supply fan uses just one coil and one magnet with 2 or 4 poles. Direct-drive record players usually use three sets of windings and three Hall effect sensors, for a smoother ride; but the basic principle is, wherever the magnet is, as determined by the Hall effect sensors, set the field in such a way as to force it a bit further round.

If the Hall effect sensor cannot see the magnet, then the motor won't be going anywhere; the coils will be energised in a fixed pattern which will force the armature into some position. This is not a problem in real life because by the time it gets there, the sensor input will have changed; and therefore, so will the energisation pattern.

Speed control is achieved by pulse width modulation. There is a control input that allows all the motor drive transistors to be turned off at once. This is fed from an oscillator whose duty cycle is adjusted to keep a constant time between pulses at the Hall effect sensor (or one of them, anyway). In a direct-drive record player, the PWM duty cycle is often very low in normal operation, so as to supply a series of tiny impulses of energy to the platter; these are smoothed out by its inertia. When starting from rest, the PWM begins at full duty, jerking the record violently into motion against static friction and then coasting until it slows back down to 33 or 45.

Your symptoms sound to me as though one of the coils is not doing its job; either because it has failed open circuit, or is not getting its drive. Inverting everything probably reduces the static friction enough for the partially-functional motor to cope, although the speed is still out of lock.

[bigfathairyvika]

Thank you JulieM .
I did think it was more complicated than I had first thought.

[julie_m]

What test equipment have you got? An oscilloscope with two inputs would be very useful, as it would allow you to see two signals at a time. But even with just a multimeter, it should be possible to determine whether the windings are OK.

You might have to disconnect the coils for a proper test; but just for a first quick sniff, measure the resistance of each of the stator coils, with the probes both ways around. If there was nothing amiss with the windings, all the forward resistances should be similar and all the reverse resistances should be similar, although the forward and reverse readings might be different for any winding due to semiconductor junctions being turned on by the test voltage (no sniggering at the back there).

How about sharing the link for the schematic? Some photos also would not hurt!

[bigfathairyvika]

I will sort the schematic and photos etc tomorrow.
Too nice a day to be stuck inside.
Btw: have four channel scope 350mhz and errr... several other scopes... cannot have too many I hope....

Mark

[G6ONEDave]

I don't know the specific deck but if it appears to do it's thing when inverted, it might be worth checking the centre shaft bearing that the centre spindle sits on when spinning. Is it there, is it worn down or possibly the bearing mount may have collapsed. I've had the collapsed mount on other decks where the bearing sits on top of a plastic end cap and the end cap has disintegrated from chemical reaction of the lubricating oil.

Dave

[bigfathairyvika]

Dave, this does indeed sit on a plastic cap for the bearing which is in a recess of the end plate.
Spins fine. no friction.

Schematic of TT200 attached, which has the motor control circuit which I would say is pretty damn near enough the same at the TT1.

Also a quick pic of the motor board, which unlike other equipment doesn't allow probing of the unit whilst the right way up!

I do have someone who is looking at another TT1 which works and is checking the existence or non-existence of a more substantial bearing.

I may even get him to drop it round.

Anyway, coils on motor check out ok.

I have a new driver chip on order as they are cheap as chips.

[TonyDuell]

That schematic shows that there are 3 hall-effect sensors used to switch the motor windings and a separate 'FG' coil (Frequency Generator) used for the speed control. I'd check round that area of the circuit.

It's on the last page of the circuit in the last post. Check round TR1, then on to IC2. It's very unlikely to be a problem with the motor driver IC1 if the thing runs at all.

I had something of a sense of deja vu when I saw that circuit. It's very similar to the scanner motor control in the Canon CX laser printers, almost 40 years old now. There was even a pin on the speed control chip in that unit labelled '33/45', but it was tied to a constant logic level of course.

[G6ONEDave]

Check that the plastic end cap is flat where it makes contact with the bearing. If it's domed out, it signifies wear and also means that there is more contact area with it and the ball bearing. If thats the case it also means that the platter will be sitting slightly lower than intended, which in a sever case will cause the platter to catch the deck plate as it rotates.

Of course the problem might be the motion detect circuit or the motor drive circuit, which will require extension cables for checking whilst the deck is the correct way up, so that you can note down the results from your test gear.

Dave

[bigfathairyvika]

Update:

The motor and drivers circuits have no faulty components.
The hall sensor and FG circuits are all doing their thing correctly.

The platter bearings and the plastic bearing are in fully working condition.

I now moving my eye over to the CPU board and the signals from that board going to the motor control board as the control signals are intermittent.

[bigfathairyvika]

SOLVED!!!

But not fixed.....


Well, after moving to the control board and checking voltages on the CPLD ( Xilinx ), the VCCINT pin is shorted almost to ground.
So, try as it may the chip didn't have much luck getting any power.
Before anyone says so, I isolated the pin and rechecked, the pin is 130R to ground internally. It should be more like several K.

Is anyone on here able to copy a working chip ( if I supply the working one from a working deck ) to a new blank one?

I haven't the facilities or knowledge to program Xilinx chips, although I suppose it can't be much harder than programming pics and atmels?

Mark

[G6ONEDave]

Hopefully your analysis is correct, if other known working chips are in the kohms but, 130 ohms at 12v is only 9.23ma current draw and at 5v is 3.846ma.

Dave

[bigfathairyvika]

Working chip 1.56K.

The VCCINT line is the supply for the internal gates to use. When they aren't doing anything (no power to vcc )
they shouldn't be using any power.
Or that's how I read it from the datasheet.
Also there appeared to be nowt happening on any of the other pins when scoped.
Also it fits the customer description of what they "accidently" did with a soldering iron. Apparently they were resoldering a wire to the 12v line with the power ON and shorted across another track! Didn't tell me this until yesterday morning....