This might help. You need a strobe and record with timing lines. It helps to have another hand to run the strobe while you adjust the speed screw.
Speed Adjustment Instructions - DC Motor with Standard PSU
Applies to TecnoDec and GyroDec or Gyro SE DC motors with standard (not VC or HR) power supplies.
Under certain circumstances it may be necessary to adjust the output voltage supplied to the DC motor,
so the turntable rotates at the correct speed.
Procedure
First the speed must be verified before going any further. Place a strobe disc on the platter to verify that
the turntable rotates at correct speed when the belt is on the 33.3 RPM groove of the motor pulley (top
groove). If the speed is too fast or slow, adjust as follows. Note: A neon or fluorescent light source makes
it much easier to read the strobe disc than with an incandescent light. Natural light will not give any
reading at all. The use of a dedicated electronic strobe gives the most accurate results, as it does not
depend on the electrical utility company for the accuracy of the 60 Hz reference frequency.
1. Unplug the DC power supply from the mains and from the motor.
2. Remove the 4 screws on the underside using a #1 Philips screwdriver.
3. Remove the top cover, exposing the printed circuit board (PCB).
4. Using the photo below, locate the blue rectangular multi-turn adjustment potentiometer, with the brass
adjustment screw.
5. Plug the DC power cord back into the motor and AC line cord into the mains. BE EXTREMELY
CAREFULL NOT TO TOUCH ANY LIVE PARTS WHEN PERFORMING THE ADJUSTMENT.
6. Turn on the turntable. While observing the strobe, adjust the speed by turning the brass adjustment
screw on the PCB in either direction until the correct speed is indicated. The speed should be set ever so
slightly fast to compensate for stylus drag while a record is playing.
7. Unplug the AC cord from the mains, and reinstall the cover on the power supply.
Rev.5