Sony AV-3420CE Service Manual

The Head Drum has a built-in dc motor thatprovides torque to rotate both the Video Head andthe Capstan. The Video Head assembly is connectedto the shaft of the dc motor. Torque is transmittedto the Capstan (M) via Drum Pulley (T) and theCapstan Belt (V). Torque is also used to drive theTake-up Reel Table (O) via the Drive Pulley (R) andthe Drive Shaft (S). The Sub-motor (X) and theSub-Motor Belt (W) are used in the playback modefor the capstan servo system.The Head Drum also has a built-in 13,125 Hzfrequency generator coil, 25PG coil, and 50PG coil.The relative position of the video heads and the PGcoils is shown in Fig. 9-2. Two output pulsesfrom the 50PG coil, 1 pulse from the 25PG coil,and 625 cycles from the 13,125 Hz FG coil areobtained for each revolution of the video heads;50 Hz, 25 Hz and 13,125 Hz are obtained at 25revolutions per second.brushesPG coilsvideo headD-c motor with13,125 Hz FGNote: FG: frequency generatorPG: pulse generatorFig. 9-2. FG and PGs9-29-2.TAPETRANSPORTINPLAYBACKMODEThe.tapetransportintheplaybackmodeisdescribed in four sections: Brake System (See 9-2-1),Pinch Roller Mechanism (See 9-2-2), Tape Take-UpSystem (See 9-2-3) and Tension Control System(See 9-2-4).9-2-1. Brake SystemThebrakesappliedtotheSupplyandTake-UpReelTablesinthestopmodearereleasedintheplaymode.SeeFig.9-3.Settingthefunctionleverfromstoptoplayrotates theFunctionSelectCamcounterclockwise.Thepinshownat(A)pushestheBrakeReleaseSlidePlateinthedirectionindicatedbythearrow,actuatingthetwo BrakeLeverstoreleaseSupplyandTake-UpReelTablebraking.9-2-2. Pinch Roller MechanismPinch Roller pressure is applied against theCapstan when the Solenoid is energized. Refer toFig. 9-3. When power is applied to the Solenoid,the plunger moves in the direction indicated by thearrow, rotating the Pinch Roller Pressure Plateclockwise and thus compressing the Pressure Spring.This causes Pinch Roller Lever (A) to rotate clock-wise, forcing the Pinch Roller against the Capstan.9-2-3. Tape Take-Up SystemDrive is transmitted from the Head Motor tothe Take-Up Reel as described below. Refer toFig. 9-1. The Sub-Belt transfers drive from theDrum Pulley on the Head Motor to a Drive ShaftPulley on the Drive Shaft. The Take-Up Belt andTake-Up Pulley couple drive torque to the Take-UpReel.