Hello, i have this turntable that sometimes turns backwards, I have already replaced C8=33uF NP, C15 and C16 100uF NP but nothing has changed.
I do not know that TT, but sounds like you have a synchronous motor in that, like in lot of turntables. This probably : https://www.ebay.co.uk/itm/296987406490 (and that looks to me just like an old Tesla motor, I had several of that in 24V version, used in my modded Nad with success).
These motors are 2 phase motors with one phase shifted 90 degrees (by the cap you mentioned). It should be connected similar to this
If you do not have one of the phase, the motor should be a lot more noisy and starting in random direction, also low torque.
What I would do is the following.
JG
These motors are 2 phase motors with one phase shifted 90 degrees (by the cap you mentioned). It should be connected similar to this
If you do not have one of the phase, the motor should be a lot more noisy and starting in random direction, also low torque.
What I would do is the following.
- find the common point (2 of the 4 motor wire should be shorted) and measure AC to the other 2 motor wires. You should measure somewhat similar. There is a Voltage drop on the cap also, but not a lot. Like if you measure 110V on the gray<>red, you should measure at least, say 90V on the blue<>gray.
- if it is there, than I would disconnect the motor and would measure DC resistance. Red<>gray and blue<>gray. It should be close together, like 50 and 54 Ohms. If one is way higher or open, or way lower you have either broken or shorted wire. I would also measure to the motor body. It should be open to all wires.
JG
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Thinking again I would measure first without disconnection. You can measure DC resistance in circuit also (but of course mains disconnected).
If you have broken/shorted winding, you may not have to throw it out. I'm not sure about this one, but I did do rewind several Philips/Airpax/Premotec motors already. Pretty easy to disassemble, remove winding and rewind. On the other hand, if you have not the proper diameter enameled wire, it may be more expensive to get rewind than just buy a new one.
JG
JG
Thanks Giordano, the motor is controlled by TDA7256B, I will insert some test points and do the checks you recommended. I had measured the two coils, with the motor unsoldered, and they gave a value of about 22 Ohm each.
You mean one TDA7296 ? (I do not find 7256) Is there a transformer in between? Or, you have 24V motor?
That would mean you have a sin generator with one output, so it is still the cap making the 90 degrees shift for the aux phase. Just like it would be fed from the mains.
Somewhere you loose one of the phases.
Can you make some pictures? I'm curious now 🙂
Thanks,
JG
That would mean you have a sin generator with one output, so it is still the cap making the 90 degrees shift for the aux phase. Just like it would be fed from the mains.
Somewhere you loose one of the phases.
Can you make some pictures? I'm curious now 🙂
Thanks,
JG
Sorry, ic is TDA7056 all the electronics are powered by 15Vdc. There is an IC CD4051 used as an oscillator and at the output of the TDA7056 there is a sinusoid at 50Hz. Both coils of the motor are powered by a capacitor. One coil is powered through a 33uF, the other coil has a 200uF (100+100 parallel.). I will try to insert the basic diagram and some photos.