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What to do when Quartz seems "off"

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What to do when Quartz seems "off"

Postby rnshwa16 » 16 Oct 2017 22:46

I recently picked up a Technics SL-5200 semi-automatic, quartz direct drive turntable, and in remarkably good condition. Aside from a cueing mechanism that seems under-damped, the only problems are the strobe and maybe the quartz accuracy. The stylus light works, but the strobe seems more like a red light than a strobe. It's useless for adjusting the correct speed.

Fortunately it's got a quartz mode. Problem solved, right? Well, maybe, if I'm content with just quartz mode and adjusting variable mode by ear. A Strobe Light app on my iPhone set to 60.0 Hz 3600 RPM, generated a strobe that seemed "jerky" in performance compared to a dedicated on-turntable strobe, perhaps the result of the multi-tasking nature of a smartphone. So I pulled out my mini fluorescent night-light to an extension cord. Still couldn't get the platter's strobe markings to show "locked". So I pulled out a printed paper strobe disk, set it on the platter, and with my fluorescent it showed stable markings. The platter on the the SL-5200 has markings for 0, plus 3% and -3%. The platter on my non-quartz SL-3300 has the traditional four bands for 33 and 45 at 50 Hz and 60 Hz and, happily, shows dead on stable.

This all seems very curious to me. Would love to get the 5200's strobe working as I think it should, but otherwise I'm happy with it.
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Re: What to do when Quartz seems "off"

Postby Spinner45 » 16 Oct 2017 23:41

The strobe light "blinking frequency" on that unit is triggered by an IC chip.
Troubleshooting the surrounding components is required.
Forget those "apps" for strobes and such, the smartphone isn't a reliable tool for diagnosing everything in the world, trust me.
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Re: What to do when Quartz seems "off"

Postby Coffee Phil » 17 Oct 2017 05:07

Hi Rnshwa16,

What Spinner45 said is so. I have not found an I-phone app which I consider worth much for turntable speed checking. He also said the internal strobe is driven from the turntable's internal quartz clock. This is also so. Note that there is only one set of strobe markings to serve for both speeds. The strobe rate has to change from 33 1/3 to 45 RPM. It is not likely the mains frequency for either speed.

The fluorescent light which you used apparently dates from when non electronic ballasts were used so it is good for a turntable strobe. The reason it did not work with the markings on the platter is that they are not for a mains driven strobe. The paper strobe disc is a good solution, but if you want the internal strobe to work some troubleshooting will be required.
The internal strobe lamp is likely driven from a divider chip via a driver transistor. I'm guessing that the transistor is shorted causing the lamp to remain continuously. To be sure we would have to look at the drive waveform at the base or gate of the drive transistor.
A manual would be useful but there is only the user manual in the library. If you have an oscilloscope, I would suggest that you secure the manual and upload it to the library so we can talk you through the troubleshooting.

Phil


rnshwa16 wrote:I recently picked up a Technics SL-5200 semi-automatic, quartz direct drive turntable, and in remarkably good condition. Aside from a cueing mechanism that seems under-damped, the only problems are the strobe and maybe the quartz accuracy. The stylus light works, but the strobe seems more like a red light than a strobe. It's useless for adjusting the correct speed.

Fortunately it's got a quartz mode. Problem solved, right? Well, maybe, if I'm content with just quartz mode and adjusting variable mode by ear. A Strobe Light app on my iPhone set to 60.0 Hz 3600 RPM, generated a strobe that seemed "jerky" in performance compared to a dedicated on-turntable strobe, perhaps the result of the multi-tasking nature of a smartphone. So I pulled out my mini fluorescent night-light to an extension cord. Still couldn't get the platter's strobe markings to show "locked". So I pulled out a printed paper strobe disk, set it on the platter, and with my fluorescent it showed stable markings. The platter on the the SL-5200 has markings for 0, plus 3% and -3%. The platter on my non-quartz SL-3300 has the traditional four bands for 33 and 45 at 50 Hz and 60 Hz and, happily, shows dead on stable.

This all seems very curious to me. Would love to get the 5200's strobe working as I think it should, but otherwise I'm happy with it.
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Re: What to do when Quartz seems "off"

Postby davidsrsb » 17 Oct 2017 05:13

Look at the strobe light through your phone camera, it may show some "beating" effects if it is actually flashing
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Re: What to do when Quartz seems "off"

Postby rnshwa16 » 17 Oct 2017 05:50

Thanks, Phil. Your comments explain a lot. And David, I followed your suggestion to check the strobe through my iPhone's camera. I saw nothing that looked like "beating", so it would seem it is not flashing at all. Whatever role the quartz is playing in driving the strobe, based on my fluorescent it at least is properly locking the speed.

Phil, you're right VE has no service manual for the SL-5200, but there is one for the fully automatic SL-5300. But given that I'm not a technician, and don't have access to an oscilloscope, it likely won't help me. As long as it runs at locked speed, I expect I can live with this little deficiency. Compared to my SL-3300, this one has a newer, lighter arm, slightly lower rumble, a muting circuit, and a stylus light. So I'm still inclined to keep the '52 and pass the '33 to my brother. Unless this one failure portends others down the road?
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Re: What to do when Quartz seems "off"

Postby Coffee Phil » 17 Oct 2017 08:18

Hi Rnshwa16,

I think it is unlikely that the problem will affect the rest of the machine. The problem is most likely a shorted Q 201 or a shorted C228. I'd suggest replacing the transistor with a PN2222A but the Japanese transistor may have a current limiting resistor internally in series with the base. I'll try to look up the Japanese part and let you know.

OK, I checked, Q 201 is a regular PNP transistor. Try to get the OEM 2SD637 but if it is not available a PN2222a should work.

Phil

rnshwa16 wrote:Thanks, Phil. Your comments explain a lot. And David, I followed your suggestion to check the strobe through my iPhone's camera. I saw nothing that looked like "beating", so it would seem it is not flashing at all. Whatever role the quartz is playing in driving the strobe, based on my fluorescent it at least is properly locking the speed.

Phil, you're right VE has no service manual for the SL-5200, but there is one for the fully automatic SL-5300. But given that I'm not a technician, and don't have access to an oscilloscope, it likely won't help me. As long as it runs at locked speed, I expect I can live with this little deficiency. Compared to my SL-3300, this one has a newer, lighter arm, slightly lower rumble, a muting circuit, and a stylus light. So I'm still inclined to keep the '52 and pass the '33 to my brother. Unless this one failure portends others down the road?
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Re: What to do when Quartz seems "off"

Postby davidsrsb » 17 Oct 2017 16:51

PN2222A is NPN, so it seems is the 2SD637.
BCE pinout
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Re: What to do when Quartz seems "off"

Postby Coffee Phil » 17 Oct 2017 17:28

Woops! You are right! I went brain-dead. The older I get, the more that seems to happen.

Sorry,

Phil

davidsrsb wrote:PN2222A is NPN, so it seems is the 2SD637.
BCE pinout
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Re: What to do when Quartz seems "off"

Postby Doug G. » 18 Oct 2017 06:30

You're not alone, Phil. Lately, while online, I have found myself typing a reply or whatever and leaving a complete out of a sentence.

:D

Doug
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