External Control Unit
The turntable control circuitry and power supply are contained within a separate Control Unit that connects to the turntable via a cable. The Control Unit contains a transformer, a switch for external voltage adjustment (120V or 220V), a power supply PCB that supplies separate voltage feeds of +15.1, -15.1, +25.7, -25.7, and +8.0 VDC, small PCB that is used to alter the dynamic compensation parameter when the DS-20 Outer Disk Stabilizer is used and the logic control PCB. The independently supplied + and - voltages available to the logic card are used in a circuit design that allows, via trim pots, independent adjustment of the positive and negative voltages of the sine wave that is sent to the motor. Another trim pot for wow and flutter adjustment allows adjustment of the shape of sine wave that is sent to the motor.
Using an oscilloscope, a wow/flutter meter, and the service manual, the electronics can be adjusted to optimize the deck to phenomenal specifications. Periodic adjustments are recommended, as electronics components values change over time. When the motor bearing is cleaned and lubricated, the electronics rebuilt with all new capacitors, and adjustments are set with oscilloscope and meters, the deck is optimized and playback is stunning. A 20-wire umbilical connects the Control Unit to the turntable. An aircraft-quality JAE (Japan Aviation Electronics Industry, Ltd.) connector with threaded collar securely mates the Control Unit cable to the back of the deck.
The L-07D external Control Unit shown above.
The Control Unit with the cover removed, shown above. (The Logic PCB in this one had some severe damage from prior attempts to change IC's by multiple prior technicians. Traces were damaged on both sides of the board, requiring some elevated sockets to restore continuity to all IC pins.)
Rebuilt Power Supply with new capacitors, diodes and transistors
Rebuilt Logic PCB. Capacitors are all new. All other components on this card were up to spec.
This logic PCB was badly damaged by a shorted power supply caused by a former technician who gave up. The short circuit was found and corrected. The power supply was rebuilt and proper voltages were restored. I replaced all the IC's in sockets, all transistors, diodes, capacitors and the crystal oscillator on this logic PCB. The resistors and trim pots were O.K.
Control Unit next to the deck
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