MTD Y725 User Manual download pdf

LBI-38393A

Printed in U.S.A.

MAINTENANCE MANUAL

FOR

FRONT CAP ASSEMBLY

19D901913G2

TABLE OF CONTENTS

DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front Cover

CIRCUIT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front Cover

LCD Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front Cover

Control Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Front Cover

Control Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Receiver Audio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

MTD and TMX8825 (or TMX8810) Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Power Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

SERVICE NOTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

ASSEMBLY DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

OUTLINE DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

SCHEMATIC DIAGRAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

IC DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

DESCRIPTION

Assembly 19D901913G2 consists of a Liquid Crystal

Display (LCD) Assembly, a Control Panel, a Control Board,

and an internal speaker. The microprocessor on the Control

Board converts the Control Panel switch closures to serial data

which is applied to the main radio processor on the Logic

Board. The Control Board microprocessor also converts the

display serial information from the Logic Board to the data

format needed by the LCD. The Control Board contains the 3

watt audio power amplifier to drive the internal speaker.

CIRCUIT ANALYSIS

LCD ASSEMBLY

The alphanumeric LCD assembly provides all of the dis-

play indicators and the POWER on/off switch. Serial com-

mands from the Logic Board (A1) are sent to the Control

Board microprocessor (U725) on the DISPLAY SERIAL

line through P701. The microprocessor converts the serial

data to the data format needed to drive the LCD driver IC on

the LCD Assembly.

LEDs behind the LCD provide backlighting and receive

power from SWA+. The POWER switch momentarily

grounds the POWER SW line which drives the A+ switching

circuitry on the System Board (A5).

CONTROL PANEL

The Control Panel provides all controls to operate the radio

except the POWER switch. LEDs inside the panel provide

backlighting and receive power from +5 VDC. The panel

connects to the Control Board microprocessor input port pins

through J726. The microprocessor converts each switch clo-

sure to serial data which is sent on the KEYPAD SERIAL line

through P701 to the Logic Board (A1). The microprocessor

port pins are normally pulled high to +5 volts through 50K

ohm resistors in the microprocessor. A switch closure on the

Control Panel grounds an input port line. The diodes on these

lines protect the Control Board microprocessor from static

discharges.

1 2 3 4 5 6 7 8

Summary of Contents

Page 1 - 19D901913G2

LBI-38393APrinted in U.S.A.MAINTENANCE MANUALFORFRONT CAP ASSEMBLY 19D901913G2TABLE OF CONTENTSDESCRIPTION . . . . . . . . . . . . . .

Page 2 - LBI-38393 LBI-38393

CONTROL BOARDMicroprocessor U725 on the Control Board uses two serialdata lines to send and receive data with the main radio processoron the Logic Boa

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ASSEMBLY DIAGRAM(19D901913, Rev. 6)LBI-38393 LBI-383932

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OUTLINE DIAGRAMCONTROL BOARD19D902233G2FRONTCAP(19D902233, Sh. 2, Rev. 0)(19D902863, Layer 1, Rev. 0)COMPONENT SIDE(19D902233, Sh. 2, Rev. 1)(19D90222

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SCHEMATIC DIAGRAMCONTROL BOARD19D902233G2(19D902864, Sh. 1, Rev. 0)LBI-38393 LBI-383934

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SCHEMATIC DIAGRAMFRONTCAPCONTROL BOARD19D902233G2(19D902864, Sh. 2, Rev. 0)LBI-38393 LBI-383935

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PARTS LISTSYMBOL PART NO. DESCRIPTION- - - - - - - - - -ASSEMBLIES- - - - - - - - - - A6 Control Board19D902233G2- - - - - - - - - - CAPACITORS- - - -

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IC DATAU801AUDIO AMPLIFIER19A701830P1FRONTCAPU725MICROCOMPUTER(CHMOS 8-BIT)19A704345P11U727VOLTAGE REGULATOR19A704970P1U803OPERATIONAL AMPLIFIER19A701