Sharp vc-ga56z Service Manual

Contents

21VC-GA56ZVC-GH96Z4-18. ADJUSTMENT OF TAPE DRIVE TRAIN1. Tape run rough adjustment1 Remove the cassette housing control assembly.2 After shortcircuiting TP803 and TP802 provided atoperation PWB, plug in the power cord.3 Check and adjust the position of the tension pole.(See 4-12.)4 Check and adjust the video search rewind backtension. (See 4-10.)5 Connect the oscilloscope to the test point for PBCHROMA envelope output (TP201). Set the syn-chronism of the oscilloscope to EXT. The PBCHROMA signal is to be triggered by the headswitching pulse (TP202).6 Set the alignment tape (VROATSV) to play. (Put a500g weight on the cassette tape to prevent lift ofcassette tape.)7 Press the tracking button (+), (–) and change theenvelope waveform from max to min and from minto max. At this time make sure that the envelopewaveform changes nearly parallel.8 Unless the envelope waveform changes nearlyparallel, adjust the height of supply side and take-up side guide roller so that the envelope waveformchanges nearly parallel. (For envelop adjustmentprocedure refer to Figure 4-35.)9 Turn the tilt screw to remove the tape crease at thefixing guide flange.Playback the tape and check for tape crease at thefixing guide flange.(1) If there is no tape creaseTurn the tilt screw clockwise so that tape creaseappears once at the flange, and then return thetilt screw so that the crease disappears.(2) If there is tape creaseTurn counterclockwise the tilt screw so that thetape crease disappears.(Reference) If the tilt screw is turned clockwisecrease appears at the lower flange.Notes:1. Previously set the tracking control in the center posi-tion, and adjust the envelop waveform to maximumwith X value adjustment nut. Thereby the tape runrough adjustment is facilitated.2. Especially the outlet side envelope waveform musthave higher flatness.2. Adjustment of A/C head height and azimuth1 Perform the initial setting of A/C head position bythe method stated in "4-15 Replacement 3".2 Connect the oscilloscope to the audio output termi-nal.3 Using the alignment tape in which 1 kHz linearaudio signal has been recorded, adjust the heightscrew so as to get max audio output.4 Using the alignment tape in which 7 kHz linearaudio signal has been recorded, adjust the azimuthscrew so as to get max audio output.5 The adjustment of 3 and 4 twice or three timesrepeat, and finally adjust 4.3. Tape run adjustment1 Connect the oscilloscope to PB CHROMA enve-lope output test point, set oscilloscope sync to EXT,trigger-input the PB CHROMA signal (head switch-ing pulse).2 Rough adjustment of X valueTentatively fix A/C head arm screws 1 and 2 by themethod described in 4-15 "Replacement 3".Playback the alignment tape (VROATSV) andshortcircuit TP801 and TP802. As a result the auto-tracking is automatically cancelled, so that the Xvalue adjustment mode is set.Move the A/C head with the X value adjustmentgear driver (JiGDRiVER-6) by the method shown inFigure 4-33, and adjust the A/C head so as to getthe maximum envelope waveform. (Note: Whenthe A/C head is adjusted, adjust so that the maxi-mum envelop waveform is obtained nearest theposition of initial setting made in 4-15.)Guide roller500gWeight of 500gCassette TapeFigure 4-31.Figure 4-32.For X value adjustmentAdjust the X value, turning thegear-type screwdriver.Figure 4-33.