Technics Sp10 Woes

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Wolfgang Felber
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#31 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Yes I do, it is etched into my brain. I used the ground probe of the scope onto C1 and the main probe onto C2 of the drive board. I was trying to measure the waveform of the 50K oscillator circuit. AS soon as I did that, it blew a fuse and that was it. I feel like a complete fool.
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Nick
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#32 Re: Technics Sp10 Woes

Post by Nick »

So, is that C1 on the drive board that is connected to the 32v supply?

So I would think the effect of shorting the 32v supply would either kill the regulator or take some of the tracks out feeding that voltage.For the future only connect the scope ground to the 0v line.

Have you checked the power rails now? Is the 32v line ok?
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Wolfgang Felber
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#33 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

HI Nick, I still have 32.5 volts, the reason I say that is the plunger for the brake still works fine, you can hear the clicking every time you press the on/off button. All of the voltages appear to be OK. To be sure I will measure them again tonight. Thank you for being patient.
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#34 Re: Technics Sp10 Woes

Post by Nick »

Check the voltages. If it was 50v, it would still work solenoid.

Check you still have 32v on C1 and C2 point to make sure that PCB track not damaged. After then measure all voltages on connectors to that board. That will be place to start.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Wolfgang Felber
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#35 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick, I dont know if this is significant but I notice when I press the button to start the platter spinning, I notice a couple of things. 1. the driver transistors get very hot very quickly. 2. the strobe light goes out completely and when you press the button to shut it off the strobe comes back up again. Does this sound like a dead short somewhere? I did a dry test on the motor on the weekend, I disconnected the drive board and connect the multimeter to A1 an AC, A2 and AC, A3 and AC, I then spun the motor slowly using a battery drill, I took a reading and got 6.59 volts AC on all of the coils. Does this mean the motor is OK? As I said before the DC resistance across all coils is approximately 13 - 14 ohms.
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Nick
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#36 Re: Technics Sp10 Woes

Post by Nick »

No idea, its hopeful for the coils, but I can't say or know. The strobe is a 140v neon, if the voltage drops it will go out. If the drive transistors are pulling more current than they should (which they sound like they are doing because they get hot) the it may pull the supply down and cause the neon to go out.

If you shorted C1 to ground, you need to look at what that may have done, everything else may be a symptom of that.

Did you try

"Check you still have 32v on C1 and C2 point to make sure that PCB track not damaged. After then measure all voltages on connectors to that board. That will be place to start."

If you did then maybe post them.

Also check with the scope that the 50k oscillator is running.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Wolfgang Felber
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#37 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick, thanks for that, so that I don't do any more damage using the scope, which points do I use to test the 50K oscillator? C1 or C2 for the probe and ground point for the ground. I will get stuck in tomorrow night and get back to you with a whole pile of results. heres hoping.
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#38 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick So I can understand what is happening, the 50k oscillator creates an AC voltage so that you can get inductive voltage going to the hall sensors when the motor spins, does it also give you the AC voltage for the driver transistors to move the motor? the crystal gives you the different speed frequencies through the divider network. If the 50k oscillator isnt working, does that mean the driver transistor are getting just DC? Sorry I am trying to get my head around the whole process. I am correct, I read somewhere this is the most technically involved turntables ever? Except maybe the SP10R.
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Nick
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#39 Re: Technics Sp10 Woes

Post by Nick »

The 50k energises the set of coils in the motor, that signal is picked up by the matching three phase coils and is used as input to the three phase motor driver stage. It avoids having to generate a 3 phase drive signal electronically.

You had a working turntable. You shorted c1 to ground, so start with what that short will have damaged, see if the oscillator is working first. See if there is 32v at the C1 point.

I keep repeating this. You need to measure the test points where there are signals shown on the schematic and see if they are the same or different.
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#40 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick, I think I did what you said. First off, I did not get a 50 kilohertz signal on the scope. I have 32.79 volts at C1, in fact, I have taken the reading from all of the connection points on the driver board, they are as follows: a3 0.0 volts b1 0.067 volts b2 0.067 volts b3 1.111 volts b4 1.413 volts b5 1.384 volts a2 23.3 volts C1 32.79 volts C2 32.78 volts PC 20.95 volts P3 20.95 volts P2 20.95 volts P1 20.95 volts AC 22.18 volts A3 22.18 volts A2 22.18 volts A1 22.18 volts a1 32.79 volts. I will try again to get the rest of the measurements tomorrow. I did replace TR 28 with the correct transistor 2sc1328.
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Nick
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#41 Re: Technics Sp10 Woes

Post by Nick »

Ok, check with the scope at C2, C1 is connected to the supply rail so you won't expect AC there.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Wolfgang Felber
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#42 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi Nick, as if this job could'nt get any more difficult, my scope just stopped working. Checked the fuse,that was OK. So I can only assume the SMPS is on the fritz. Should have taken up Plumbing. At least I know what I am doing.
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#43 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Hi, success, got the scope working again, it was a 48 cent resistor between the main power cap and the TOP247yn offline switcher. Now that I am back up and running, I shall keep you posted. The worst thing is I purchased a new 1054z scope, now I have two, I struggle to use one let alone two. I shall try and test test oscillator and get back to you. I have learnt quite a bit about switch mode power supplies over the last month.
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#44 Re: Technics Sp10 Woes

Post by Wolfgang Felber »

Sorry forgot to mention, found out what the other board was for, it was for the external cueing. I have removed it and brought it back to original wiring layout.
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pre65
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#45 Re: Technics Sp10 Woes

Post by pre65 »

I'm pleased that you have finally got a result.

Well done.
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