Yes I understand that it's a different stories. Do you think it's worth not to pair mk2 pcb with the old motor? The only differece between these motors is only that old motor is bigger=)
Bigger and with different internal resistances.
You are the only that can decide if its worth it or not and you are the only one that can determine what works and what doesn't.
You need to try and recreate the same conditions that the motor would see in the original board. That means setting the board up to deliver the same drive voltage across the motor. The later board has two amplifier stages to enable it to drive the motor with two voltages that are out of phase with each other. So you have to decide whether you can get the old motor to run off just one of the amplifier sections, or whether you can reduce the amplitude of the drive and use both sides of the bridged amplifier.
Do you understand the bridge concept... as one side goes up, the other goes down. That gives you twice the voltage to apply to the motor... which the old motor doesn't need. So you need to find a way to fix that by either using just one side of the bridge or by reducing the amplitude of the drive signal. There are a lot of presets on that board. Are some of those for setting amplitudes ?
You are the only that can decide if its worth it or not and you are the only one that can determine what works and what doesn't.
You need to try and recreate the same conditions that the motor would see in the original board. That means setting the board up to deliver the same drive voltage across the motor. The later board has two amplifier stages to enable it to drive the motor with two voltages that are out of phase with each other. So you have to decide whether you can get the old motor to run off just one of the amplifier sections, or whether you can reduce the amplitude of the drive and use both sides of the bridged amplifier.
Do you understand the bridge concept... as one side goes up, the other goes down. That gives you twice the voltage to apply to the motor... which the old motor doesn't need. So you need to find a way to fix that by either using just one side of the bridge or by reducing the amplitude of the drive signal. There are a lot of presets on that board. Are some of those for setting amplitudes ?
I disconnected red wire on both mk1 and mk2 motors. Both are rotating!
The torque of just one coil is enough to start and rotate this motor. I think the problem will be with the heavy platter and everythis is installed.
The torque of just one coil is enough to start and rotate this motor. I think the problem will be with the heavy platter and everythis is installed.
So both behave the same.
If I had this problem then I would look at reducing the amplitude of the drive voltage. Can you do that with the presets ? You will have to see what the service manual says on that. You would need to reduce it by around 50%. If you don't then the motor might run hot.
If you can reduce the amplitude then try wiring the motor up to both amplifiers... in other words just swap the motors over following the connections on the diagram.
And replace those transistors.
You will only know by experimenting with this... I haven't got definite answers for you on this.
Over and out for today 😉
If I had this problem then I would look at reducing the amplitude of the drive voltage. Can you do that with the presets ? You will have to see what the service manual says on that. You would need to reduce it by around 50%. If you don't then the motor might run hot.
If you can reduce the amplitude then try wiring the motor up to both amplifiers... in other words just swap the motors over following the connections on the diagram.
And replace those transistors.
You will only know by experimenting with this... I haven't got definite answers for you on this.
Over and out for today 😉
Only !
Go and experiment with it and see if you can reduce the amplitude while keeping a good sine shape.
Ok. lets take 45 speed. PCB2 gives me 6V to the mk2 motor. To what voltage should I reduce it with the mk1 motor?
Hi terrom,
Take it easy and slow down here! I don't want to butt into what Karl is telling you.
Some of those controls will change the frequency and others vary the level of the drive voltages. Set with the variable speed control centered.
Measure the DC resistance of the old motor and compare that to the MKII motor. It might give you some clues. Try and find the service manual for the MKI version and read it. Set up the MKII board to deliver what the MKI anual says the older motor needs. If you have to pay for a manual, do so. That's cheap compared to the value of the working TT. Blindly guessing will only lead to trouble. You have the MKI board don't you? What transistors does it use?
Wait for Karl to come back to your thread. You have some homework now, so occupy yourself with that for now.
-Chris
Take it easy and slow down here! I don't want to butt into what Karl is telling you.
Some of those controls will change the frequency and others vary the level of the drive voltages. Set with the variable speed control centered.
Measure the DC resistance of the old motor and compare that to the MKII motor. It might give you some clues. Try and find the service manual for the MKI version and read it. Set up the MKII board to deliver what the MKI anual says the older motor needs. If you have to pay for a manual, do so. That's cheap compared to the value of the working TT. Blindly guessing will only lead to trouble. You have the MKI board don't you? What transistors does it use?
Wait for Karl to come back to your thread. You have some homework now, so occupy yourself with that for now.
-Chris
Ok. But the mk1 service manual tells me that I should have 8V across the coils of the motor on the 45 speed while mk2 service manual tells me to have 6V ac. I checked it by my DWM. this is excactly what Ihave now. So when I connet mk1 motor to the mk2 pcb I have 6V across the coils intead of 8V and the motor rotates. What ismy next step if I want to go " reduce the amplitude of the drive and use both sides of the bridged amplifier" method!
Hi terrom,
Okay. Stop and think now. What does the manual say about the drive voltage for the MKI motor?
Those are the conditions you have to duplicate. You are driving the motor, so you have to supply what that motor wants to see. Think about it.
-Chris
Okay. Stop and think now. What does the manual say about the drive voltage for the MKI motor?
Those are the conditions you have to duplicate. You are driving the motor, so you have to supply what that motor wants to see. Think about it.
-Chris
You will have to find out by trying and by adjusting one set to get a feel for what they do and what range they have.
Not yet. And its no big deal if they go pop.
Be clear on your measurements. That could mean one of two things. I would take your own readings and work with those. Use the scope and note the amplitude of the signal from each amplifier on the Mk2 board. Both should be similar. That is the voltage on each of the two drive wires to the motor.
Those voltages are out of phase with each other. So if you have sine wave going 6 volts positive and 6 volts negative on each single wire then the voltage across the motor (across both wires) is double that. That is what a bridge amp does. It lets you deliver twice the voltage that you would otherwise get.
The Mk1 motor was fed from a single amplifier with one wire tied to the positive supply via a cap. Its up to you to figure out if the motor will run when fed from the bridged amplifier. If it does then you should try and reduce the amplitude of the drive voltage so that it matches the original amp. The value for the bridge amp will be one half the voltage swing of the Mk 1 amp.
You have 6 volts across each coil with the bridge amp. That is giving 12 in total and so you should try and reduce it a little (the presets).
No problem 🙂 you go for it 😉
One problem I had with a TD125 was poor contacts. WD40 was the cure. Always check the silly things first. I am not saying this is the reason here. It might help someone who has just found one.
So should I reduce the voltage to 4 volts? So if we double it by the bridge it will be 8v as it was on the mk1 pcb?
Yes. If you can get 4 volts from the amplifier in the bridge then the total across the motor is 8 volts.
Hi Karl,
Nope, you have everything well in hand.
Can you imagine the arguments at Thorens when they were deciding on the bridged drive for the motor? The old guard won out in MKI, the new guy won with the MKII.
-Chris
Nope, you have everything well in hand.
Can you imagine the arguments at Thorens when they were deciding on the bridged drive for the motor? The old guard won out in MKI, the new guy won with the MKII.
-Chris
I could see on the scope that the second frequency on the mk1 pcb floating a little on the peak of the sinewave while on the Mk2 both sinewaves are stable
Hi terrom,
Check to see if that second frequency is line related. Does that waveform stay stable if you change your oscilloscope trigger to line?
-Chris
Check to see if that second frequency is line related. Does that waveform stay stable if you change your oscilloscope trigger to line?
-Chris
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