Nakamichi OMS-1A, OMS-1E Service Manual

Service Information

			OMS.1/1A/1E								Nakamichi
Model			(Compact Disc Player)
			from	-
Serial No.											No. 00D - s1 - 3110 (1/36)
Subject			Principle of Operation								Date 31 May 1988
CONTENTS
1.	Introduction											1
2. Power Supply Circuit					••..................		•...		••...............................			3
3.	Control System •			..	•............	•.........		•..........		•.•..•..•	...............	3
4.	Reset Circuit .•..................					••••............			•..	••.•....................		6
5.	Eject/Load Operations ................					•...........			••....	•......................		6
	(1)	Eject Operation			.....................		, ................................... .					7
	(2)	Load Operation			.........................................................						.	7
6.	Auto Power Control											8
7.	Focus Servo System				. , , , ................ , • . .				. . . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	9
8.	Tracking Servo System . . . . . . . .					. . . . . . . . . .	• . . .		. . . . . . . . .	. . . . . . • . . . . . . . . . . . . . . .	• . .	12
9.	Feed Servo System			. . . . • . . . . . .		• . . . . . . . . . .		. .	. . . . • . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	14
10.	Track Jump System				. . . . . . . . . . .	. . . . . . . . . .	.	. .	• . . . . . . . .	. . . . . . . . . . . . . . . . . . . . . .	• . .	15
11.	CLV (Constant Linear Velocity) Servo System .........................................											18
	(1)	EFM Auto Slice Circuit . . . . . .				. . . . . . . . . .	.	. .	. . . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	20
	·(2)	PLL Circuit . . .			. . . . . . . . . . .	. . . . . . . . . .	.	. . .	. . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	21
	(3)	CLV Servo Circuit .................................								: ......................		22
12.	Signal System . . . .			.	. . . . . . . . . .	• . . . . . . . . .	• . . .		. . . . . . . .	. . . . . . . . . . . . . . . . . . . . . .	• . .	23
	(1)	Frame Sync. Detector and EFM Demodulator ......................................										23
	(2)	Subcode Demodulation . . . . . .				. . . . . . . . . .	.	. . .	. . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	24
	(3)	RAM Interface (External RAM Address Generation) .							. . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	26
	(4)	Error Correction .			. . . . . . . . . .	. . . . . . . . . .	.	. . .	. . . . . . . .	. . . . . . . . . . . . . . . . . . . . . . .	. .	26
	(5)	Playback Flag Determination and Interpolation					.....................................					26
	(6)	Digital Filter and DAC (D/A Converter) Interface ....................................										28
	(7)	DEMO (Pin 24 of IC141) Signal				...............................................						29
	(8)	D/A Converter and Following Circuits ...........................................										30

1.Introduction

Fig. 1 shows the block diagram of the OMS·1, and Fig. 2 shows its timing chart. Though being Nakamichi low-cost version CD player, the OMS·1 incorporates a variety of technology developed for Nakamichi'shigh-grade models and demonstrates high-grade sound quality.

The OMS-1 employs a 3-beam laser pickup. In circuit construction, third-generation LSls particularly developed for CD players, 2-times oversampling digital filter, up-to- date D/A (digital-to-analog) converter technology, and 5th-order active low-pass filter are employed. In mechanism, the floating disc drive with precision

centering is adopted for protection against disturbance.

Using the Remote Control Unit attached to the OMS-1 enables F. Fwd. and Rev. operation which cannot be executed on the OMS-1 itself.

G-880505A Printed in Japan

OMS-1/1A/1 E OOD-Sl-3110 (2/36)

Loser P1ckup

IC 101

+~V -~.~V

t t

~!ii~._·_··_·_·..__..._·_,F'"=a:

Conuot Switch

IC402

MPll Remote	RM60t Romote
Control Ooco<ler	Conttol Rocei•tr

2-1.rne ovo ..omptinQ

DiQitol filter

IC302

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1C311,312

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Somp\e8 Hold

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SMP 2

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Re'"\

to MPV 6i IC141

Fig. 1

Block Diagram

Ejecl/LoM

Eject/Load<with Disc)

Ploy

F.Skip

R.Skip

Pouse

Ploy

Stop

Truy Open

(EJeCtl

!IC261-4l

r----t-- <Lood>

Troy Clos•-

Loo<linQ Motor

Open/Close

-

1__

Switch

•

feed Motor

Outer

Circle

f

c1c221-8J

Inner

Cir

cl•/

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Inner

Switch

lh

-

FOC\IS Seorch

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-

Kick Pu\$e

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!lCIOl-10>

Line Output

~

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Notes: 1. This timing chart starts from Standby mode without putting a disc.

2.Signal marked with *is not a continuous signal.

3.Disc Motor signal shows a CLV servo signal.

4.Kick pulse is a complex signal of JP+ and JPsignals.

Fig. 2 Timing Chart

OMS-1/1 A/1 E OOD-Sl-3110 (3/36)

2.Power Supply Circuit

Fig. 3 shows the power supply circuit of the OMS·1. In the power supply circuit of the OMS-1, the power trans-

former has two windings on its secondary side. One is used for the digital circuit and another is for the analog

circuit to avoid interference between the digital and analog circuits.

Ground lines of the digital circuit and analog circuit are connected contig.uous to a point where the power trans· former is connected to the Main P.C B. Ass'y. The F'.C.B.

patterns are also designed to eliminate interference between ground lines following the connection point.

The DC power supply for the digital circuit provides non-

regulated ±12	V as well	as regulated +5 V and -5.5 V.
The DC power supply for the analog circuit provides
regulated ±10	V.	Fig. 3 Power Supply Circuit

3.Control System

Two MPUs (microprocessing units; IC401 and IC402) are		select each mode.
incorporated on the Main P.C.B. Ass'y of the OMS-1. Fig.		IC401 outputs display control signal corresponding to
4 shows the keyboard and display control circuit. IC401		each mode to turn ON the LED on the Control P.C.B.
(LC6520H-3527) on the Main P.C.B. Ass'y is an MPU for		Ass'y.
system	control. IC402 (LC6528C-3509) receives and	Fig. 5 shows the system control circuit.
decodes	command signals sent by the Remote Control	IC401 decodes signals entered from keys on the Control

Unit RM-1CD, and then transmits them to IC401. Each

P.C.B. Ass'y, and transmits them to the Digital Signal

command entered

from

the key

is

input

into

IC401 to

Processor IC (IC141; LC7860N).

-

P.C.B.I

co NTROL

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Fig. 4 Keyboard and Display Control Circuit

OMS-1/1A/1 E OOD-Sl-3110 (4/36)

The servo commander in IC141 is controlled by COCK (IC401-26), COIN (IC401-25), and RWC (IC401-30) output by IC401.

8-bit 1-word data is output from COIN of IC401 synchronously with COCK wh&n RWC is set to "H". This data is output in LSB first order.

Four kinds of commands are output from IC401. They are Focus Start command, Disc Motor command, Track

Jump command, and Mute command. Table 1 shows command codes.

Fig. 6 shows the timing chart of RWC, COCK, and COIN.

The command is executed from trailing edge of RWC. As Mute and Disc Motor commands are latched to the

registers, the command type varies according to the other commands input. When IC401 and IC141 are reset by Reset signal, Mute command is -= dB and Disc Motor

command is in Stop mode.

Although approximate 25ms is needed for execution of the Track Jump command, the next Track Jump

command can be given during execution of the previous

one. The Focus Start command requires more time, but other commands cannot be input during execution of

this command. Thus when more than one command is to be input, the Mute or Disc Motor command is input first followed by input of the Focus Start or Track Jump

command.

DACLK (4.3218 MHz) generated by the crystal timing generator in IC141 is input into clock circuits of IC401 and IC402. IC401, IC402, and IC141 are reset by the

Reset signal generated when the Power switch of the

OMS-1 is turned ON or OFF.

Table 1					Command Codes
M	L
s Code	s				Command
B	8
00000000				Nothing
00010001				1 Track Jump In #1
00010010				1 Track Jump In #2
00010011				4 Track Jump In
00010100				16 Track Jump In
00010101				64 Track Jump In
00011001				1 Track Jump Out #1
00011010				1 Track Jump Out #2
00011011				4 Track Jump Out
00011100				16 Track Jump Out
00011101				64 Track Jump Out
00010110				256 Track Check
00000001				Mute 0 dB
00000010				Mute -12 dB
00000011				Mute-= dB
00000100				Disc Motor Start
00000101				Disc Motor CLV
00000110				Disc Motor Brake
00000111				Disc Motor Stop
00001000				Focus Start

#1 JP Pulse width 233 µs + 233 µs.

#2 Switching from acceleration pulse to deceleration pulse is made by detecting the intermediate point of the track.

MAIN P.C.8.

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Fig. 5 System Control Circuit

OMS-1/1A/1 E OOD·Sl-3110 (5/36)

RWC ~~~~~~~~~~~~-
<IC 141-71 l _j	L_

CQCK

<IC141-75l

COIN

<ICl41-74J

Fig. 6 Servo Command Timing (from IC401)

Fig. 7 shows the wireless remote control receiver circuit.

This is a circuit for receiving commands sent from the

Remote Control Unit RM-1CD. Signals are received by photodiode 01 (PH3028) in the remote control receiver unit RM601 (BX-1407), and amplified through current-to- voltage conversion by the head amplifier section in IC

CX20106A.

Then, the limiter amplifier section limits surplus parts of signal waves, and the band-pass filter whose center fre-

quency is 40 kHz suppresses out-of-band noise component. Then, the detector detects signal component, the integrator integrates it, and the hysteresis comparator outputs rectangular waveform command signal. Fig. B shows output waveform at pin 7 of CX-20106A.

Then, the waveform is input into pin 16 of IC402 and decoded. Decoded command signal is transmitted to IC401 to control the OMS-1.

CONTROL

P.C. B.

MAIN

P.C.B.

.,, -~

RM601

SX-1407

Rtmoto Control Receiver Unit

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IC402

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Wireless Remote Control Receiver Circuit

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Pin N.;..7

I

Output

Waveform LJ L,___o_"_'_____I

-++-4.5ms

Fig. 8

Wireless Remote Control Receiver Output

OMS-1/TA/1 E OOD-Sl-3110 (6/36)

4.Reset Circuit

Fig. 9 shows the reset circuit of the OMS-1.

This circuit is provided to prevent MPUs and IC141 from malfunctioning as well as to prevent any noises from being output from line output terminals when the Power switch of the OMS-1 is turned ON or OFF.

Setting the OMS-T's Power switch to ON rises the power supplies in the DC power supply of the Main P.C.B. Ass'y. When +12 V is output, emitter voltage of 0531 reaches approx. 6 V. Since base voltage of 0531 is lower than the emitter voltage while C533 is being charged, 0531 is turned ON during the charging.

When 0531 is turned ON, 0313 and 314 are turned ON to mute line output terminals. When 0531 is turned ON and its collector voltage exceeds 3 V, ZD141 is turned ON, 0141 is turned ON, and the Reset signal= Lis input into IC401, IC402, and IC141 to reset them.

When C533 has been charged, base voltage of 0531 reaches approx. +6 V; consequently, 0531 is cut off and collector voltage of 0531 lowers up to approx. -5 V. By this, 0141 is cut off, and IC401 and IC402 are released from the reset state after C154 has been charged. Further, IC141 is released from the reset state after C138 has bee.n charged. Now the OMS-1 is ready for operation.

When the Power switch is turned OFF, C533 is immediately discharged through D532. Since emitter voltage of 0531 is approx. +6 V by voltage charged in C532, 0531 is turned ON, and its collector voltage rises

MAIN P.C.B.

							.,,
+12v							..
"~							~~
		0531	0531			Rl46	Z0141
		MA700	2SAl317lS,T!			"'"
			1!533
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							0.01µ

up to approx. +6 V. Thus, similarly to turning ON the Power switch, Reset signal= Lis applied to IC401, IC402, and IC141, and line output terminals are muted.

Fig. 10 shows the timing chart of the reset circuit.

		ON		OFF
Power		J	·~
Switcll
+ 12V		+:J	·~
0531-E		+~	·~
0531-8+~~
		·~:.		l'--
0531-C		: .....____, r-----1
IC401-23		'
		+5V - + --- 1
IC402-4		___ J	-
IC141-76		~ ! ------ ,

0313-B +O 6V

0314-B-~~

	0313-C						---,--; s-------'l__
	0314-C
				Z: Hi9ll Impedance
			Fig. 10 Reset Timing Chart
		!C402	LC6528C-3~Q
,_
	---->1Rese1
		!C401	LC6520H-3S27
	"-
	+----11...1
	1!145	!C\41 LC7860N
	IOOK 76 _
		11 ..u

			1!341
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			0313
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Fig, 9 Reset Circuit

5.Eject/Load Operations

Eject/load operations take place when a CD is loaded or unloaded.

Fig. 11 shows the eject/load circuit.

Usually, eject/load operations are triggered by press of the

Eject/Load button on the Front Panel Ass'y.

When loading a CD, however, the Play button may be pressed to permit direct operation. In this case, the Play mode is automatically entered after loading.

(1) Eject Opeation

Pressing the Eject/Load button with the Disc Tray Ass'y closed starts eject operation and moves the Disc Tray

Ass'y out. Upon press of the Eject/Load button, the signal Eject/Load = L is input to pin 6 of the IC401 (LC6520H· 3527) on the Main P.C.B. Ass'y.

Receiving the signal Eject/Load - L, IC401 outputs "H" from pin 8 (LM-). Since this upsets the input balance of IC261 (LA6500), positive voltage is output at pin 4 of IC261. The Loading Motor is applied with approx. +4.5

V, so it rotates in the reverse direction to move the Disc

Tray Ass'y out. When the	outward movement of the Disc
Tray Ass'y actuates the	Open/Close	switch, the	signal
Open = L is input to pin	6 of IC401	and pin 9	(LM+)

changes from "H" to "L". Because the input balance of

IC261 is now restored, the Loading Motor stops, and the eject operation is over with the Disc Tray Ass'y left out.

The eject operation can be entered from any mode. Fig.

12 shows the timing chart of the eject operation.

(2) Load Operation Refer to Figs. 13 and 14.

Pressing the Eject/Load button or the Play button with the Disc Tray Ass'y open starts load operation and closes the Disc Tray Ass'y.

When the Eject/Load button is pressed, the signal Eject/ Load = L is input to pin 6 of IC401 on the Main P.C.B. Ass'y. __

When the Play button is pressed, the signal Play = L is input to pin 4 of IC401. Upon receipt of this signal, IC401 outputs "H" level from pin 8 (LM-).

Since this upsets the input balance of IC261, a negative voltage is output at pin 4 of IC261. The Loading Motor is applied with approx. -4.5 V, so it rotates in the forward direction to close the Disc Tray Ass'y.

When the closing motion of the Disc Tray Ass'y actuates the Open/Close switch, the signal Close = L is input to pin 5 of IC401, and pin 8 (LM-) changes from "H" to "L" level. Because the input balance of IC261 is now restored, the Loading Motor stops and the Disc Tray Ass'y closes.

OMS·1/1A/1E OOD-Sl-3110 (7/36)

Then, when pin 3 (Pickup Inner) of IC401 is at "H" level, the Feed Motor is rotated, and after the Pickup Inner signal is changed to "L", the Read-In area is read to terminate the load operation.

If the Pickup Inner signal is already at "L" level, the Feed Motor is rotated slightly to make the pickup direction forward, so that the Pickup Inner signal is set to "H" level. Then the Feed Motor is rotated in the reverse direction to set the Pickup Inner signal to "L" level. Now the Read-In area is read to terminate the load operation.

If the load operation was started with the Play button instead of the Eject/Load button, the Play mode is

entered after the load operation.

Eject/Load

IIC4016l

LM+

IIC401-Ql

Loadin9

Motor

Open

IIC401-6l

approx.

~--~f--'<--+4.5V

Fig. 12 Eject Timing Chart

Eject I Locd <IC401-6l

LM-

!IC401-8)

Locdinq Mctor

IToSe

CIC401-5l

Reeding of _____,n_ ReodIn Arec

Fig. 13 Loading Timing Chart (When Eject/Load switch is pressed)

MAIN

P.C.8.

CONTROL

P.C.B.

Plcy

S'w'601

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CIC401-4l

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Close

UC401-5l

IC401

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n

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LM+~~==ri-

Fig. 14 Loading Timing Chart

Ej<e\ Stoll

(When Play switch is

Fig. 11

Eject/Load Circuit

pressed)

OMS-1/1A/1 E OOD-Sl-3110 (8/36)

6.Auto Power Control

Fig. 15 shows the auto power control circuit of the OMS-1 which mounted on the Laser Pickup Ass'y. The auto power control circuit has two functions: (1) control of the laser diode so that the amount of light emission is not affected by temperature changes, etc., and (2) protec-

tion of the laser diode against overcurrent.

Overcurrent into the laser diode leads to breakdown or deterioration of the laser diode. The semi-fixed volume is incorporated in the Auto Power Control P.C.B. Ass'y of the Laser Pickup Ass'y. This volume must never be adjusted because it has been exactly adjusted in our factory.

The laser diode of the OMS-1 emits light if:

(1)The Disc Tray Ass'y is loaded.

(2)The OMS-1 is in Play or Pause mode.

However, during reading of the Read-In area at the load time, the laser diode emits light even if the OMS-1 is not in Play or Pause mode.

When the Disc Tray has been loaded, the Open/Close switch on the CD Mechanism Ass'y is switched to close side, so that the signal Close = L is input to pin 5 of IC401. Then, pressing SW603 (Play) or SW604 (Pause) on the Control P.C.B. Ass'y causes input of the signal Play= L or Pause = L to pin 4 or 3 of IC401, so that pin 10 (LSON) of IC401 outputs the signal LSON = L. Since the LSON = L signal enters pin 38 (LDSW) of IC101 (LA9200), the laser ON/OFF circuit is turned ON and approx. -5.5 Vis output at pin 39 (LOO) of IC101. Then this voltage enters the APC (auto power control) circuit and turns ON 02, 03, and 01, so that the laser diode of the Laser Pickup Ass'y emits light.

The amount of light emission from the laser diode is detected by the monitor diode of the Laser Pickup Ass'y and fed back to base of 02 in the APC circuit. This feedback signal is compared with the -2.3 V reference voltage at emitter of 02. If the feedback signal is lower than -2.3 V, the current flowing in the laser diode increases. If the feedback signal is higher than -2.3 V, the

current flowing in the laser diode decreases. Thus, the laser diode is controlled to emit a constant amount of light.

When pin 10 (LSON) of IC401 is set at "H" level, the laser diode does not emit light, because 02, 03, and 01 are cut off.

To measure the current flowing in the laser diode, determine the voltage across R2 (22!1) in the APC circuit using a DC voltmeter. Then calculate the current from the formula I= V/22.

The timing chart related to laser diode light emission is given in Fig. 16.

For measuring the laser power of the OMS-1, it is not necessary to bring the OMS-1 into Play mode or Pause mode. It can be measured easily only by grounding TP401 on the Main P.C.B. Ass'y, causing the laser diode to emit light.

Eject/Load

!IC40l-6l

Close (1C401-5)

Play or Pouse
LSON		ITT
<IC401-10l	' -------

Fig. 16 Laser ON/OFF Timing Chart

CONTROL P.C.B.

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Fig. 15 Auto Power Control Circuit

7.Focus Servo System

Fig. 17 shows a block diagram of the focus servo system.

The focus servo has the function of maintaining a fixed distance between the laser pickup's object lens and the

CD's signal surface.

As the CD begins rotation, the focus servo shifts the object lens of the laser pickup vertically so that the distance to the signal surface is constant at any given time.

The vertical deviation of a CD is specified to be within ±0.5 mm. The focus servo of the OMS-1 uses the astigmatism method. This method is illustrated in Fig. 18 showing the construction and in Fig. 19 showing the principle of operation.

The cylindrical lens shown in Fig, 18 plays an important role in the astigmatism approach. This lens acts as a lens only in one direction (x-direction in Fig. 18), but it does nothing in the other direction (y-direction in Fig. 18). Therefore, at point B, the light is condensed into a vertical (y-direction) line, and at point A, into a horizontal (x- direction) line. An enlarged view of optical path between points A and B is presented in Fig. 19. At the midpoint J between points A and B, the beam takes a circular form.

At points nearer to point B (farther from point J), the beam shape becomes a progressively longer ellipse extend- ing in the vertical direction. At points nearer to point A, the beam shape becomes a progressively longer ellipse

extending in the horizontal direction.

In the astigmatism method, the object lens is adjusted so that the image of CD's signal surface is formed at point J when the signal surface is on the focal plane of the optical system. With a quarter-split PIN photodiode placed at point J as shown in Fig. 19, the four outputs are arithmetically operated in the formula "(A + C) - (B +

D}". The result of this arithmetic operation, which is zero, serves as the focus error signal.

When the CD is nearer to the object lens, the image on the quarter-split photodiode at point J becomes a vertically longer ellipse, giving a positive focus error signal. When the CD is farther from the object lens, the image becomes a horizontally longer ellipse, giving a negative focus error signal. Thus the focus error signal is bipolar.

C====:;::;==:;:== IVertical deviation of CO
n				±0.Smm
	Pickup			Focus Error			Focus Coll
				Detector			Driver

Fig. 17 Focus Servo System Block Diagram

OMS-1/1A/1 E OOD-Sl-3110 (9/36)

Laser Diode

Sylindrical

Lens

A

•

CD's Signal Surface

Fig. 18 Astigmatism Method

A

Too Close

Good

Too Far

Focus Error

Signal

+V

ov

-v

Fig. 19

OMS-1/1A/1E OOD-Sl-3110 (10/36)

Fig. 20 shows the focus servo circuit of the OMS·1.

The focus servo circuit of the OMS-1 is located in the Main P.C.B. Ass'y. It consists of IC401 (LC6520H·3257), IC141 (LC7860N), IC101 (LA9200). IC201-2/2 (LA6510). focus control circuit, and peripheral circuitry.

The	focus servo	is control led primarily by	IC401 and
IC141.
Fig.	21 shows the	RF amplifier circuit for the focus servo
and	the EFM signal. This circuit performs		current·to-

voltage conversion of output from the quarter-split photodiode.

Output of the quarter-split photodiode is input into the Main P.C.B. Ass'y first: Through A + C and B + D accumulation it is input into pins 41 and 42 of IC101. IC101 amplifies input signals through current-to-voltage (I - V) conversion. -(A + C) signal and -(B + D) signal processed through current-to-voltage conversion are wired-

When the Focus Search command is transmitted from IC401 to the servo commander in IC141, IC141 causes the servo commander to output the FST signal (from pin 14), and discharges C147 (100 µF, 10 V) through R137 (180 Q). At this time, the object lens of the Laser Pickup

Ass'y lowers.

Then, IC141 causes the servo commander to output the FOGS signal (from pin 13) to pin 20 of IC101 (FOGS) and the Focus Control P.C.B. Ass'y to deactivate the

focus servo.

Simultaneously, it charges C147 (100 µF, 10 V) through R143 (68 kil). At this time, the object lens of the Laser Pickup Ass'y rises slowly.

The focus zero detector section in IC101 detects the S-curve of the focus error signal (as shown in Fig. 23).

This £.curve is detected when it gets almost in focus.

ORed by resistors of 10 kQ, inverted and amplified by the RF summing amplifier. and output from pin 36 of IC101 as the EFM signal (A+ B + C + D). On the other hand, the 1-V processed signals are differentially amplified by the focus error amplifier and output from pin 31 of IC101 as the focus error signal [(A+ C) - (B + D)]

In general, the focus servo circuit executes focus searching

first. When the focus zero detector signal is detected,

focus searching terminates, and focus servo is activated.

Further control is in accordance with the focus error signal.

Fig. 22 shows the focus search circuit.

O MAIN P.C.8.

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Fig. 21 RF Amp. Circuit

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Fig. 20 Focus Servo Circuit

When the S-curve signal lowers than -0.6 V, FZO = L signal is output from pin 18 of IC101 and input into pin 15 of IC141. For generation of FZO signal, refer to Fig. 24.

When the FZO = L signal is input, the servo commander in IC141 resets the FOCS signal. By this, FOCS= L signal is output from pin 13 of IC141. This signal is input into pin 20 of IC101. Since pin 30 of IC101 (FSW) is consequently brought into the high-impedance state, focus error signal is input into the focus coil driver, activating focus servo, and the focus error signal controls the focus coil.

After outputting the Focus Search command, IC401 examines input signal into pin 39 (ORF) to check whether focus servo is activated. If focus servo is not activated during charging C147, IC401 outputs the Focus Search command again.

OMS-1/1A/1 E OOO-Sl-3110 (11/36)

The ORF signal is generated in IC101. Output signals from the quarter-split photodiode are summed and amplified by the RF summing amplifier in IC101 to be the EFM signal, and is input into the peak hold section and bottom hold section. The ORF signal is set to "H" if voltage at pin 35 (PHLO) is 0.45 V. It is set to "L" if PH LO voltage is 0.42 V.

The object lens of the Laser Pickup Ass'y is located at the mechanical zero point, i.e., in the lower position when the

Power switch of the OMS-1 is set to OFF. When the

Power switch is turned ON, it moves up to the electrical zero point, i.e., a point where 0.5 V is applied across the focus coil. Based on this point as the center, the object lens moves up and down for focusing.

VR101 (100 kill is for adjusting offset of the focus error amplifier, and VR102 (10 kill is for adjusting focus gain.

MAIN P.C.8.

		0102		0101
				VRl02
				'°'
	0.6V j			"'"" rocu• Goio		IC20l
Focu• Zero ~ l				~"l
				'" R203		LAl>510
Douctor	30			"'		'7 212'
		'"1		---R\44;:;:;::+~~&"					-n
					IOOK c"	C203	'°"''
				~		C202	R206
						0.111	'°'

1-f'~'~~<•H>--~,~,,,_._~~~~~~~--. >
160	rgi

Fig. 22 Focus Search Circuit

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Fig. 23 Focus S-Curve

FOCS	I'
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-150••1--

Focu.s Error

FZO

Fig. 24 Timing Chart