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Does anyone have a Yamaha 700 P turntable & know how to adjust the speed so it locks on the proper speeds for 33's & 45's?
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Here's a link to the Vinyl Engine and the owners/maint. manuals. You will need to register to download. It's Free!
Good luck
Thank you!
It is servo controlled so you shouldn't normally need to adjust the reference speed unless something has failed in which case you should send it in to someone for servicing. Internally there MAY be a pitch control adjustment pot (probably under the platter if they intend for you to be able to adjust pitch). However, if you can't see anything obvious, leave it well alone otherwise you might never get it back to the reference condition.
If it is similar to the Technics SL1200, you will need an oscilloscope to measure the frequency of the reference signal being fed to the motor controller. In the case of the SL1200 it is 160kHz and therefore beyond the capabilities of a simple multimeter. I honestly don't think you should attempt to twiddle any knobs under the lid unless you can find the service manual.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Closest I could find was for the P-751, from the same vintage roughly. Vinyl Engine. Looking at the schematic for the 751 it appears the entire motor speed control is in 2 IC's with just a few external components, no speed adjustment trim-pots. The speed lock LED is binary, on=speed locked to xtal reference, off= not. Its kinda useless.The 751 service manual shows only how to connect an oscilloscope to see the speed control waveform (you need to build a little buffer amplifier with one transistor to make the 'scope connection!) and there is no way to adjust or fix it in the manual. You just look at it see if it's sour and start replacing components till it's pretty, I guess.
The entire speed control (for the 751, possibly the same for the 700?) is on a single PC board attached to the motor coils. It's a very basic system. That board has several electrolytic capacitors it's possible that one (or more) of them is dead. It does not appear that there is an external speed sensor, the servo is established from a coil somewhere in the motor PC board.
I hate the words "no user serviceable parts inside" but in this case it seems true... short of looking for fried electrolytic or replacing them systematically. A couple things you might try first, beyond looking for obvious busted stuff, fuzzballs, and dead bugs might be 1. check the voltage from the power supply is reasonable (the 751 is 24v), 2. see that the motor turns freely (if not, de-gunk the bearing) and 3. spray contact cleaner in the motor speed switch in case it is erratic. Otherwise, maybe start thinking of saying goodbye to the ol' 700- on eBay the dustcover should be worth something.
Bear sez: "Don't electrocute yourself"
Edits: 07/22/17 07/22/17
Thank you for your honest & up front advice! Will see if I can locate the service & Owners manual online!
I have a Technics table that I ran for years. The speed would get unstable if I let it go to long without lubing it. I would try that first.
Dave
Good to know that! Will try that first!
To clarify the difference, a quartz locked motor has a reference timing signal which is generated by an oscillator circuit that includes a quartz crystal; the motor also generates a timing signal which is derived from the speed of rotation, and the two signals ares compared in the phase locked loop (PLL)
So for a turntable with a quartz locked motor, there is no need to adjust the speed, because the reference signal is stable.
In a conventional DC motor, the reference is generated with a voltage divider and there is no timing signal to compare the motor speed with. Temperature, load and other factors cause the speed to drift over time, so a pot is needed to fine tune speed.
Your turntable does not have any speed adjust because the motor is driven by a quartz locked PLL circuit.
Best regards,
Thank you very much for your information!
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