Tandy 1400LT - Page 136

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Check D5,D7,

R26,R42 and

Pin7

IC38:LOW BATT2

. .

Under 10. 8-11.4V

GATE3.

Check Battery

voltage at D4,D6.

Check voltage

at Pin2,6 (t5V)

and 8(t12)

IC38.

ICheck IC38 and

5-21

Main Page

Table of Contents2
Part 1 . Introduction10
System Overview11
External View11
- Front View12
- Rear View12
Hardware Specifications16
- DISASSEMBLY I NSTR Uctlo NS20
Case Screw Removal20
- Lever Disengagement20
- Top Case Removal21
- Cable Removal21
Top Case20
Battery Cover and Rear Cover22
LCD Frame. Buttons. and LCD22
- Battery Cover and Rear Cover Removal22
- Lever Spring Removal22
- Top Cover Removal23
- Exploded View of LCD Assembly24
- Cable Cover and LCD Removal24
LED PCB and Keyboard25
Arm Assembly Removal25
Battery Pack26
Base Frame26
- Battery Connector Removal26
Right Side of Base Frame26
- Left Side of Base Frame27
Connector Locations27
Fdd28
- Power Switch Cord Removal28
- FDD Removal28
Power Source PCB. Power Source PCB Cover and Power Source PCB BOX29
- Exploded View of Power Source Assembly29
- FDD Cable. Expansion Bus Cable. Modem Cable and Memory Cable30
- Bottom View of Base Frame30
Contrast Knob31
Speaker31
Contrast Knob Removal31
Speaker Removal31
Main PCB. Keyboard Shield Plate. Rear Panel and Rear Panel Cover32
- Exploded View of Main PCB Assembly32
Pedestals. Handle and Bottom Case33
- Bottom Case Dismantling33
Battery Pack Replacement34
Theory of Operation38
General38
Organization of Section38
Block Diagram39
IV-3. Description of Block Diagram40
Cpu40
IV-5. Clock Generator (Custom IC)41
- Clock-Gen.141
Clock-Gen.242
Clock-Gen.342
Clock-Gen.443
IV-6. Memory Map44
Memory-Map44
DIP-SW Location44
IV-7. RAM Control Circuit45
IV-8. Memory Card Specification47
- Memory-Card47
IV-9. ROM Control Circuit48
- ROM Address Decoder Circuit48
ROM and Peripheral Circuitry48
I/O Address Map49
IV-10. I/O Address Map49
Clock Speed50
- Interrupt52
- IV-12. Keyboard53
- External Keyboard53
KEYBOARD-2 (Internal Keyboard Character Codes)62
KEYBOARD-4 (Enhanced Keyboard Character Codes)68
KEYBOARD-5 (Numeric Lock States)70
- Floppy Disk Drive71
  - DMA Control72
  - FDD Control73
- Cpu Interface for FDC73
- FDD Interface Circuitry74
- VFO and FDC Interface75
External FDD Connector Pin Assignments76
- IV-15. Printer Interface77
- Printer Interface Circuit77
- Timing Diagram between CPU and Printer78
- IV-16. LCD Controller79
  - CPU Interface79
- LCDC-CPU Interface79
  - VRAM-CPU Interface80
- VRAM-LCDC Interface80
- VRAM-LCDC Timing Chart81
  - LCD Unit Interface82
- Interface Signal between LCDC and LCD Unit82
- LCD Interface Timing Diagram83
  - NTSC Composite and IRGB Interface84
- NTSC COMPOSITE Interface84
- IRGB Interface84
- NTSC COMPOSITE Interface Timing Diagram85
- IRGB Interface Timing Diagram86
- IV-17. Serial Interface87
- Serial Interface Block Diagram87
- Pin Layout Definitions of UART87
- Switching Logic (RS232C. MODEM)88
Baud Rate Generator (1.8432Mhz)88
- RS232C Interface Circuit89
- Internal Modem Connector and Peripheral Circuitry89
- RTC and Peripheral Circuitry90
- IV-19. Speaker Circuit91
- Speaker Block Diagram91
- IV-20. Power Supply92
- EL Output Waveform92
- Power PCB96
- Power PCB Circuit Diagram-297
- Power PCB Circuit Diagram-398
- IV-21. Option99
  - Expansion Bus99
Expansion 1/0 Connector99
- Internal MODEM Connection101
Modem101
Part V . Troubleshooting110
- FDD Disassembly. Assembly and Parts146
- FDD Motor Spindle Parts Location148
- FDD PCB Control Parts Location149
- Parts List150
  - MAIN PCB Assembly150
Dip-Sw152
- POWER PCB Assembly157
- SUB PCB Assembly160
- MEMORY PCB Assembly161
- LED PCB Assembly162
- LCD Unit Assembly163
- Fdd164
- Keyboard Unit Assembly171
- Circuit Diagrams176
- Main PCB Circuit Diagram176
Pcb Views198
- VIII-1 MAIN PCB Views198
Main PCB199
- Vlll-2 POWER PCB Views200
- Vlll-5 MEMORY PCB Views202
Appendices203
- Lcd Specifications204
- Block Diagram204
  - Mechanical Specifications205
- Dot Dimensional Drawing205
  - Electrical Specifications206
- VO Adjusting Circuit207
- Timing Chart211
  - Optical Characteristics212
- Optical Characteristics Measurement System212
  - Definition of and213
- Definition of Contrast Ratio213
  - Operational Precautions215
- Operational Precautions216
- Unsoldering el Terminals (Bottom View218
- Detaching el (Right Side View218
- EL Removal219
- EL Insertion220
- Attaching el (Right Side View)221
- Soldering el Terminals221
- Functional Diagram224
  - Disk Chucking Mechanism226
- Interface Connections227
  - Recommended Circuit228
Input and Output Level228
- Step Pulse Timing230
- Write Data Timing (MFM230
  - Write Gate and Write Data Timing231
- Index Signal Timing232
- Track 00 Signal Timing232
- Read Data Timing232
Timing of the Spindle Motor Rotation235
Power Supply and Current235
- VCC Detector236
- Cable Connections237
Signal Connector Pin Assignments238
Mechanical Dimensions239
- Recommended Mounting Direction240
- Mounting Angle240
- Cartridge Loading241
Allocation of the Track Format243
Appendix D . 3.5 Inch FDD MAINTENACE246
Tools and Measuring Instruments246
Trouble Shooting247
- Cat's Eye Pattern249
- Index Phase250
Parts Replacement253
- Replacement253
- Front Panel Replacement254
- Carrier Replacement255
Adjustment258
- Head Alignment258
- Index Alignment258
Appendix E . CHARACTER CODE TABLE260

Tandy 1400LT - Page 136

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