SONY DF181
Service Manual

Focus/Tracking Gain Adjustment A servo analyzer is necessary in order to perform this adjustment exactly. However, this gain has a margin, so even if it is slightly off, there is no problem. Therefore, do not perform this adjustment. Focus/tracking gain determines the pick-up follow-up relative to mechanical noise and mechanical shock when the 2-axis device operate. However, as these reciprocate, the adjustment is at the point where both are satisfied. � When gain is raised, the noise when 2-axis device operates increases. � When gain is lowered, it is more susceptible to mechanical shock and skipping occurs more easily. This adjustment has to be performed upon replacing any of the following parts : � Optical pick-up � RV503 (Focus gain) � RV502 (Tracking gain) Normally, be sure not to move RV503 (focus gain) and RV502 (tracking gain). � Focus Gain Adjustment � Procedure : This adjustment is not performed. If focus gain RV503 is turned, set to mechanical center. � Tracking Gain Adjustment � (perform at normal operation) [MAIN BOARD] (Side B)

1. Place the optical pick-up level, horizontally. (If the optical pickup is not level, the 2-axis device will be weighted and adjustment cannot be done.) 2. Connect the oscilloscope between IC501 0 pin (TEO) and #º pin (VC) on the MAIN board. 3. Set the disc (YEDS-18) and Press the ^ (+) key. 4. Turn RV502 slightly clockwise (tracking gain drops) and obtain a waveform with a fundamental wave (waveform has large waves) as in Fig. 1 . 5. Turn RV502 slowly counterclockwise (tracking gain rises) until the fundamental wave disappears (no large waves) as in Fig. 2. 6. Set RV502 to the position about 30°counterclockwise from the position obtained in step 5. If RV502 contact point is more than 90° counterclockwise from mechanical center, tracking gain is too high. In this case, readjust from step 4. 7. Press ^ (+) or = keys and observe the 100 track jump waveform. Check that no traverse waveform appears for both ^ (+) or = directions. (See Fig. 3 and 4.) It is acceptable if the traverse waveform appears only now and then, but if it appears constantly raise tracking gain slightly and check step 7 again. 8. Check that there is no abnormal amount of operation noise (white noise) from the 2-axis device. If there is, tracking gain is too high, readjust starting with step 4. The waveforms are those measured with the oscilloscope set as shown below. � VOLT/DIV : 50mV � TIME/DIV : 5mS � Waveform when tracking gain lowered. Fundamental wave appears (Large amplitude appears.)
0V

oscilloscope (DC range) IC501 !º pin (TEO)
+ �

Fig. 1 � Waveform when fundamental wave disappears (Large amplitude does not appear.)
0V

IC501 #º pin (VC)

Fig. 2 � Waveform when no traverse waveform during 100 track jump. (Brake application is smooth because of adjustment.)
IC501
0V
30 10

100 track jump waveform

Fig. 3

� Waveform when no traverse waveform during 100 track jump. (Brake application is poor because of adjustment.)

0V

100 track jump waveform traverse waveform

Fig. 4

� 10 �