Tandy 1400LT - User Manual

Tandy@ 1400LT
LAPTOP COMPUTER
Catalog Number: 25-3500
SPECIFICATIONS
Microprocessor
Clock Speed
Operating System
Memory
Keyboard
LED Indicators
Display
Disk Drives
Modem
External Connections
AC Adapter
Battery
Other Features
Dimensions
Weight
NEC V-20 (8088 equivalent).
7.16/4.77 MHz (switchable).
Includes MS-DOS/GW-BASIC 3.2
16K ROM, 768K RAM. 640K accessible by MS-DOS, 128K available
for RAM-based disk drive or
print spooler.
Full-size, 76 keys.
Caps Lock, Num Lock, Low Battery, Scroll Lock, Standby Mode.
Backlit “Supertwist” LCD, 640
X 200 pixels, 80 X 25 characters, aspect ratio 1 : 1.4. Optional
RGBI Color Monitor.
Two internal 720K 3.5 inch double-sided, double-density.
Optional 1200-baud, Hayes-compatible mode.
AC Adapter
DB-25 Parallel Printer.
DB-9 Serial Port.
RGBI Color Monitor.
Composite Video
Out.
External Disk Drive.
Enhanced Keyboard.
15 VDC 700mA, UL listed.
Removeable 12 Volt, 2200 mAh. 4 hours
of continuous use.
Battery-powered Clock/Calender, Standby Mode and Speaker.
3-1/2
X 14-1/2 X 12-3/8 inches
13.5 lbs.
I
01988. Tandy Corporation
All Rights Reserved.
Tandy is
a registered trademark of Tandy Corporation.

Summary

I INTRODUCTION

1-4 Hardware Specifications

Details the core technical specifications of the computer's hardware components.

II. DISASSEMBLY INSTRUCTIONS

IV. THEORY OF OPERATION

IV-4. CPU Details

Explains the function and features of the NEC V20 CPU.

IV-5. Clock Generator Operation

Details the operation and clock speeds generated by the custom IC.

IV-6. Memory Map and Organization

Shows the memory organization and address decoding.

IV-7. RAM Control Circuitry

Explains the DRAM refresh control and address strobe generation.

IV-10. I;O Address Map

Lists the I/O addresses and their corresponding functions.

IV-11. Interrupt Handling

Explains the interrupt processing functions and sources.

IV-12. Keyboard Interface

Describes the internal and external keyboard interfaces and data codes.

IV-13. External Keyboard Protocol

Details the communication protocol for the external keyboard.

IV-14. Floppy Disk Drive Operation

Explains the FDD peripheral circuitry and DMA operation.

IV-15. Printer Interface Circuit

Describes the printer interface circuit and timing diagrams.

IV-16. LCD Controller Functionality

Details the LCD controller's support for display devices and CPU interface.

IV-17. Serial Interface Details

Explains the RS232C and modem connector interfaces.

IV-18. RTC Circuitry

Describes the Real Time Clock (RTC) circuit and its peripheral circuitry.

IV-20. Power Supply System

Details the system DC power supply and its voltage/current outputs.

PART V. TROUBLESHOOTING

Does it start?

Diagnostic flowchart for power-on and startup issues.

DC;DC Converter Check

Troubleshooting steps for the DC/DC converter circuit.

Memory Check

Diagnostic procedures for memory-related issues.

LCD Check

Troubleshooting steps for the Liquid Crystal Display (LCD).

EL Check

Diagnostic procedures for the Electroluminescent (EL) back light.

Internal Keyboard Check

Troubleshooting steps for the internal keyboard functionality.

RTC (Real-Time Clock) Check

Troubleshooting steps for the Real-Time Clock circuit.

Printer Interface Check

Diagnostic procedures for the printer interface.

Internal FDD Troubleshooting

Steps to diagnose and fix issues with the internal Floppy Disk Drive.

External FDD Troubleshooting

Steps to diagnose and fix issues with the external Floppy Disk Drive.

RS-232 C Check

Diagnostic procedures for the RS-232C serial interface.

IRGB Check

Troubleshooting steps for the IRGB monitor output.

Composite CRT Check

Diagnostic procedures for the composite CRT monitor output.

External Keyboard Check

Diagnostic procedures for the external keyboard.

VII. CIRCUIT DIAGRAMS

VII-1. Main PCB Circuit Diagram

Shows the detailed circuit schematic for the Main PCB.

VII-2. RAM PCB Circuit Diagram

Displays the circuit diagram for the RAM PCB.

VII-4. Power PCB Circuit Diagram

B. REPLACEMENT OF EL BACK LIGHT

1. Desoldering EL Terminals

2. Detaching the EL Back Light

3. EL Back Light Removal

5. Inserting the EL Back Light Correctly

6. Attaching the EL Back Light

7. Soldering EL Terminals

C. 3.5 inch FDD SPECIFICATIONS

2. Electrical Interface Connections

4. FDD Installation

D. 3.5 inch FDD Maintenance

Outlines tools, troubleshooting, and parts replacement procedures.

D. 3.5 inch FDD MAINTENANCE

1. Tools and Measuring Instruments

2. Trouble Shooting Procedures

Provides procedures for diagnosing and resolving FDD issues.

3. Parts Replacement Guide

4. Alignment Adjustments

F. DESCRIPTION OF I;O COMMANDS

DMA Controller Address Map

Interrupt Controller I;O Map

DMA Page Registers

NMI Mask Register Function

Printer Control Register Functions

Video Controller I;O Registers

Status Register Description (3 DAH)

Register Bank Functions (3 DDH;3 DEH)

Tandy 1400LT Specifications

General

Brand	Tandy
Model	1400LT
Category	Laptop
Language	English