Sony MDS-JB920 service manual 29, Focus Bias Adjustment

8.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob so that the waveform of the oscilloscope becomes the specified value.

(When the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob is rotated, the of “EFB-

” changes and the waveform changes.) In this adjustment, waveform varies at intervals of approx. 2%. Adjust the wave- form so that the specified value is satisfied as much as pos- sible.

(Write power traverse adjustment)

(Traverse Waveform)

A

VC

B

Specification A = B

9.Press the [YES] button, and save the adjustment results in the

non-volatile memory. (“EFB = SAV” will be displayed for a moment.)

10.“EFB = MO-P”. will be displayed.

The optical pick-up moves to the pit area automatically and servo is imposed.

11.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob until the waveform of the oscilloscope moves closer to the specified value.

In this adjustment, waveform varies at intervals of approx. 2%. Adjust the waveform so that the specified value is satisfied as much as possible.

(Traverse Waveform)

A

VC

B

Specification A = B

12.Press the [YES] button, and save the adjustment results in the

non-volatile memory. (“EFB = SAV” will be displayed for a moment.)

Next “EF MO ADJUS” is displayed. The disc stops rotating automatically.

13.Press the [ÊÊÊÊÊEJECT]¤ button and remove the disc.

14.Load the check disc (MD) TDYS-1.

15.Roteto [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob and display “EF CD ADJUS” (C12).

16.Press the [YES] button and display “EFB = CD”. Servo is imposed automatically.

17.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob so that the waveform of the oscilloscope moves closer to the specified value.

In this adjustment, waveform varies at intervals of approx. 2%. Adjust the waveform so that the specified value is satisfied as much as possible.

(Traverse Waveform)

A

VC

B

Specification A = B

18.Press the [YES] button, display “EFB = SAV” for a mo- ment and save the adjustment results in the non-volatile memory.

Next “EF CD ADJUS” will be displayed.

19.Press the [ÊÊÊÊÊEJECT]¤ button and remove the check disc (MD) TDYS-1.

12.FOCUS BIAS ADJUSTMENT

Adjusting Procedure :

1.Load a test disk (MDW-74/AU-1).

2.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob and display “CPLAY MODE” (C29).

3.Press the [YES] button and display “CPLAY MID”.

4. Press the [MENU/NO] button when “C =	AD = ” is
displayed.

5.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob and display “FBIAS AD- JUST” (C13).

6.Press the [YES] button and display “ / a = ”.

The first four digits indicate the C1 error rate, the two digits after [/] indicate ADER, and the 2 digits after [a =] indicate the focus bias value.

7.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob in the clockwise direction and find the focus bias value at which the C1 error rate be- comes 220 (Refer to Note 2).

8.Press the [YES] button and display “ / b = ”.

9.Rotate the [ÊÊÊÊÊÊÊÊAMSÊÊÊÊÊÊÊÊ]- ± knob in the counterclockwise di- rection and find the focus bias value at which the C1 error rate becomes 220.

10.Press the [YES] button and display “ / c = ”.

11.Check that the C1 error rate is below 50 and ADER is 00. Then press the [YES] button.

12.If the “( )” in “ - - ()” is above 20, press the [YES] button.

If below 20, press the [MENU/NO] button and repeat the ad- justment from step 2.

13.Press the [ÊÊÊÊÊEJECT]¤ button to remove the test disc.

Note 1: The relation between the C1 error and focus bias is as

shown in the following figure. Find points a and b in the follow- ing figure using the above adjustment. The focal point position C is automatically calculated from points a and b.

Note 2: As the C1 error rate changes, perform the adjustment using the average vale.

C1 error

220

b	c	a	Focus bias value
			(F. BIAS)

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