Technics Sp10 Woes

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Nick
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Re: Technics Sp10 Woes

Post by Nick » Wed Jul 10, 2019 1:17 am

The correct setting is in the service manual. Show us what you are getting.
Resistance isn't futile it's V / I.

Wolfgang Felber
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Re: Technics Sp10 Woes

Post by Wolfgang Felber » Wed Jul 10, 2019 12:33 pm

Hi Nick, there must be something wrong, I have connected exactly as the manual said. I have taken a photo of the connections. I am still getting two saw tooth wave forms. See photos.
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Nick
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Re: Technics Sp10 Woes

Post by Nick » Wed Jul 10, 2019 1:18 pm

THat would point to a short somewhere or a fault somewhere around the sample and hold area and R186. Maybe a failed TR151.
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Wolfgang Felber
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Re: Technics Sp10 Woes

Post by Wolfgang Felber » Wed Jul 10, 2019 11:20 pm

Hi Nick, just looked at the circuit diagram and found the R186 that is supposed to be a 150K resistor. will check it tonight. also the TR151, 152, 153 & 154, they are a JFET?

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Nick
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Re: Technics Sp10 Woes

Post by Nick » Wed Jul 10, 2019 11:48 pm

Yes, its the sample and hold that implements the phase lock. the pulse samples the ramp at the position it is at the time, and that held value is then used to provide the phase lock signal to the turntable.
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Wolfgang Felber
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Re: Technics Sp10 Woes

Post by Wolfgang Felber » Fri Jul 12, 2019 1:19 am

Hi Nick, Tested the resistor between S & T, reading is 147.7K. Also tested the scope probes, just in case there was a short in them, they are both fine.
so it looks like the TR 151 could be faulty. Will check it tonight. Testing JFets is a little different to std standard transistors, is that correct?

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Nick
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Re: Technics Sp10 Woes

Post by Nick » Fri Jul 12, 2019 8:47 am

Yep, though TBH, I would just get a replacement and replace it.
Resistance isn't futile it's V / I.

Wolfgang Felber
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Re: Technics Sp10 Woes

Post by Wolfgang Felber » Fri Jul 12, 2019 11:19 am

Hi Nick, I can do that, I purchased a full set of replacement transistors, so if you ever need any.

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Re: Technics Sp10 Woes

Post by Wolfgang Felber » Sat Jul 13, 2019 4:16 am

Hi Nick, replaced TR 151 with a 2SK30a, still getting identical waveforms. I was looking at the circuit diagram and test points S & T are adjacent to TR153 & TR154, could any of these be the culprit? I will test around them and see what happens.

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Re: Technics Sp10 Woes

Post by Nick » Sat Jul 13, 2019 11:31 am

Yep maybe also check for a short somewhere. Trace back from the gate if that meet and see if the pulse appears.
Resistance isn't futile it's V / I.

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