Sony UP895 Service Manual - Page 29

4-3

UP-895/(E)

4-1.

Video Circuit

4-1-1.

BNC Input Connector - Trap Filter Circuit

A composite video signal is input from the BNC connector (VIDEO IN) to the MA-99 board.

75

Z

termination is turned on and off using a DIP switch.

After that, the input signal branches into three paths.

One is passed through a trap filter (FL1) for NTSC, and another is passed through a trap filter (FL2) for

PAL.

The other is not processed at all.

These signals are input to analog selector 1 (IC1).

Each signal is

selected by a system control and input to video amplifier 1 (IC2).

4-1-2.

nC-SYNC Generator Circuit

A nC-SYNC signal is generated from the SYNCOUT signal that is output from video amplifier 1 (IC2).

The nC-SYNC signal is also used in an AGC circuit.

4-1-3.

AGC Circuit

The signal from an analog selector 1 (IC1) branches into two paths.

One is input to video amplifier 1

(IC2), and the other is input to the AGC circuit for detecting the peak of a signal.

The gain is controlled

by a contrast amplifier in video amplifier 1 (IC2).

When an AGC function is set to ON, the peak voltage

of the input video signal obtained by the AGC circuit is controlled by a system control (IC304) so that it

is output from analog selector 2 (IC5).

When it is set to OFF, the reference voltage is controlled by a

system control (IC304) so that it is output from analog selector 2 (IC5).

The gain is controlled by

inputting the voltage to video amplifier 1 (IC2).

4-1-4.

Brightness and Contrast Control

The video signal output from video amplifier 1 (IC2) is input through a buffer (Q220) to video amplifier 2

(IC6).

For contrast control, the gain is controlled by inputting the voltage obtained using the volume on

the front panel to video amplifier 2 (IC6).

The video signal output from video amplifier 2 (IC6) is input through a low-pass filter to the brightness

control amplifier (Q7).

For brightness control, the gain is controlled by inputting the voltage obtained

using the volume on the front panel to the brightness control amplifier (Q7).

4-1-5.

A/D Conversion and D/A Conversion

The video signal output from video amplifier 2 (IC6) is converted into a digital signal using an A/D

converter and stored in memory by a memory and head control circuit.

The A/D-converted signal is converted into a video again using a D/A converter, and a sync signal is

added using analog selector 3 (EE signal).

Moreover, the sync signal is sent to analog selector 4 and

output from the BNC connector (VIDEO OUT) to the outside.

A relay (RY1) is used to switch THRUE

and EE signals and controlled by a system control.

Section	Page
Cover	1
Table of Contents	3
1.Operating Instructions	7
2.Service Information	17
2-1. Board Layout	17
2-2. Disassembly	17
2-3. Removal of Major Parts	18
2-3-1. Removal of Mechanical Block	18
2-3-2. Removal of MA-99 Board	19
2-3-3. Removal of Switching Regulator	19
2-3-4. Removal of Thermal Head	20
2-4. Tightening the Screws	21
2-5. Installation of Fan Motor	22
3.Electrical Alignment	23
3-1. AGC Adjustment	23
3-2. Video Level Adjustment	23
3-3. Brightness and Contrast Adjustment	24
3-4. Head Voltage Adjustment	25
3-5. Initialization of Print Count History	25
4.Circuit Operation Description	27
4-1. Video Circuit	29
4-1-1. BNC Input Connector - Trap Filter Circuit	29
4-1-2. nC-SYNC Generator Circuit	29
4-1-3. AGC Circuit	29
4-1-4. Brightness and Contrast Control	29
4-1-5. A/D Conversion and D/A Conversion	29
4-2. Clock Generator Circuit	30
4-3. Memory and Head Control Circuit	30
4-3-1. Reading the Serial Data from System Control	31
4-3-2. Writing in Frame Memory	31
4-3-3. Transfer from Frame Memory to Line Memory	31
4-3-4. Thermal Head Control and One-Line Memory	31
4-4. System Control Section	34
4-4-1. Reading of Keys	34
4-4-2. Reading of Function Switches	34
4-4-3. Platen Motor Control	35
4-4-4. Head Up and Down Control	36
4-4-5. Monitor of Door Sensor	36
4-4-6. Monitor of Paper Sensor	36
4-4-7. Monitor of Head Temperature Sensor	37
4-4-8. Control of Head Fan Motor (for Head Cooling)	37
4-4-9. Control of Video Circuit Section	37
4-4-10. Control of Memory and Head Control Circuit	38
4-4-11. Gamma Correction and Thermal Storage Correction	39
4-4-12. Discrimination of Video Signal to be Input	39
4-4-13. Remote Interface	39
4-4-14. Storage of Print Count History	39
4-5. Thermal Head Section	40
4-5-1. Structure	40
4-5-2. Basic Operation	41
4-5-3. Stair Generation	41
4-5-4. Temperature Correction	42
4-5-5. Line Count Correction	42
5.Troubleshooting	43
5-1. Print is Faulty	43
5-2. Print is Too Dark or Too Light	44
5-3. “Paper Sensor” is Out of Order	45
5-4. Head Operation (Up & Down) is Out of Order	46
5-5. Paper Feeding is Out of Order	47
5-6. Door (Opening and Closing) is Out of Order	48
6.Service Mode (Self-diagnostic Function)	49
6-1 Printing the Test Pattern	49
6-2. Up/Down Operation of Head	50
6-3. Feed Operation	50
6-4. Display and Clearing of Print Sheet History	51
7.Semiconductor Pin Assignments	53
8.Spare Parts	55
8-1. Notes on Repair Parts	55
8-2. Exploded Views	56
8-3. Electrical Parts List	61
9.Block Diagram	69
Overall	69
10.Schematic Diagrams and Board Layouts	71
Frame	72
KY-454	73
SE-531	73
SE-532	73
SU-52	73

Sony UP895 Service Manual - Page 29

Video Circuit, 4-1-1. BNC Input Connector - Trap Filter Circuit, 4-1-2. nC-SYNC Generator Circuit

Page 29 highlights