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Radio Shack TRS-80 Service Manual

Micro color computer
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®
TRS-80
MICRO COLOR COMPUTER
MODEL MC-10
Catalog Number 26-3011
CUSTOM MANUFACTURED FOR RADIO SHACK, A DIVISION OF TANDY CORPORATION

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Summary of Contents for Radio Shack TRS-80

  • Page 1 ® TRS-80 MICRO COLOR COMPUTER MODEL MC-10 Catalog Number 26-3011 CUSTOM MANUFACTURED FOR RADIO SHACK, A DIVISION OF TANDY CORPORATION...

  • Page 2: Table Of Contents

    TABLE OF CONTENTS SECTION PAGE NUMBER NUMBER SYSTEM DESCRIPTION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3 SPECIFICATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 7 DISASSEMBLY / REASSEMBLY - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9 THEORY OF OPERATION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 11...

  • Page 3: System Description

    SECTION I SYSTEM DESCRIPTION – 3 –...
  • Page 4 SYSTEM DESCRIPTION The MC-10 Micro Color Computer is a fully expandable microprocessor system. It is com- posed of a 6803 central processing unit, 4K of static RAM, 8K of Basic ROM, and a 6847 video display generator. The microcomputer is also interfaced to a 48-key keyboard and provides the logic to execute a 1500 Baud cassette inter- face and a RS-232 serial interface.
  • Page 5 SYSTEM BLOCK DIAGRAM – 5 –...
  • Page 6 MEMORY MAP Hex Address C000 - FFFF 16K ROM (only 8K used) 9000 - BFFF 16K I/O Slot (Keyboard and VDG control) 4000 - 8FFF 16K RAM (4K - 20K used) 0100 - 3FFF Not Used 0080 - 00FF RAM internal to the 6803 0015 - 007F Not Used 0014...

  • Page 7: Specifications

    SECTION II SPECIFICATIONS – 7 –...
  • Page 8 SPECIFICATIONS Power Supply AC/AC adaptor Input 120V/60Hz Output 8.0V/1.5A 16W RF Modulator FC (MHz) Fsc (MHz) For U.S.A./CANADA 61.25 +/-0.25 4.5 +/-0.2 67.65 Output Impedance 75 ohm RF Output Terminal RCA jack RF Output Level 1.5 - 2.8 mV at 75 ohm Central Processing Unit 6803 8-bit processor clock speed 0.89 MHz...

  • Page 9: Disassembly / Reassembly

    SECTION III DISASSEMBLY / REASSEMBLY – 9 –...
  • Page 10 DISASSEMBLY 1. Removal of Top Cabinet Remove 4 screws as shown in Figure A. 1. Unplug the units from the AC wall outlet and disconnect all cables from the rear panel. 2. Turn the computer over and remove the four screws from the case bottom. One of the screws is located under the warranty seal in the upper right corner of the case bottom.

  • Page 11: Theory Of Operation

    SECTION IV THEORY OF OPERATION – 11 –...

  • Page 12: Cpu-6803

    CPU-6803 RESET CIRCUIT The main component of this microcomputer The reset circuit is composed of switch S1 system is the 6803 CPU. This is a 40-pin in- diode D9, resistor R24, capacitor C8, and two tegrated circuit which provides the address, gates of IC U12.

  • Page 13: Detailed Tape Format Information

    The input circuit is a zero crossing detector. tor equal to 1/2 volt. Since the other input is biased at 1 volt, the comparator output is R12 is a termination resistor for the cassette output. Resistors R16 and R17 are used to bias switched to the high state.

  • Page 14: Rs-232C Interface

    RS-232C INTERFACE thus if the input voltage is greater than 2.6 volts, the comparator is turned on. The compar- The RS-232C interface utilizes a 4-pin DIN con- ator outputs are open-collector so pull-up nector (J2). This interface allows the computer resistors R8 and R9 are required.

  • Page 15: I/O Connector

    I/O CONNECTOR In addition to serial interfaces, the MC-10 also external memory modules or ROM software modules. Table 1 provides a complete list of the provides a full complement of CPU bus signals that are accessible at the 34-pin cartridge con- signals and a brief description of each.

  • Page 16: Keyboard Interface

    KEYBOARD INTERFACE The Keyboard interface for the MC-10 utilizes To read the keyboard, only one column is enabled by writing a zero to one of the eight the I/O lines of the 6803 CPU to reduce the logic required to a single six input CMOS buffer and CPU I/O lines that corresponds to that column, seven pull-up resistors.

  • Page 17: Power Supply

    POWER SUPPLY The MC-10 power supply utilizes an external In the MC-10 the 4K of RAM is shared between power pack to supply 8 VAC at 1.5 amps. This the CPU and video display generator. This is input AC voltage is connected through the accomplished by providing buffers between power switch to the bridge rectifier.
  • Page 18 Table 2. VDG Control Register Control Register Bits DMA Bits Mode Selected A*/G A*/S (INT*/EXT) Alphanumerical green Alphanumerical inverted green Alphanumerical orange Alphanumerical inverted orange Semigraphics Four Table 3 COLOR TV SCREEN PINS VDG DATA BUS COMMENTS CSS INV Character Color Background Border Display Mode Detail...

  • Page 19: Device Selection

    DEVICE SELECTION A 74LS155 is used along with four OR gates allows an external device to change the MC-10 memory map. Also, the disable signal for the and two inverters to provide device selection in the MC-10. The 74LS155 uses A15 and A14 to memory write is ORed with A12 to prevent a divide the memory map into four 16K seg- complete overlap of the 4K of RAM into the 16K...

  • Page 20: Ram

    MODULATOR The MC6847 (VDG) has access to the RAM dur- The outputs from the MC6847 are connected ing the low portion of the E clock. Also during directly to the modulator. The modulator unit is the low portion of E, the signal AS is used to built around the MC1372.

  • Page 21: Troubleshooting

    SECTION V TROUBLESHOOTING – 21 –...
  • Page 22 TROUBLESHOOTING VIDEO INTERFACE Problems with the MC-10 may be separated into Almost all of the work for the video interface is two major areas - I/O problems and dead com- performed by the VDG (U11 - MC6847). There- puter problems. If the computer will display the fore, this chip is the most likely source of a sign-on message, then a fairly simple set of video problem.
  • Page 23 RS-232 INTERFACE ground. If this shows zero resistance, the prob- lem is a short to ground. The RS-232 interface uses three simple level If the +5 output is not shorted, check the volt- converter circuits. Isolating the problem will be age with the power pack plugged in.
  • Page 24 ADJUSTMENT OF VSB (vestigial side band) FILTER CH. 4 Make Connection according to Figure 7 Luminance In CH. Select 0.01 CH. 3 MDV - 1 Sound In RF OUT C117 RF Out JACK 0.01 5 ± 0.1V C116 75Ω Coaxial L102 L103 L101 Cable...

  • Page 25: Parts List

    SECTION VI PARTS LIST – 25 –...
  • Page 26 PRINTED CIRCUIT BOARD PARTS CAPACITORS Ref.No. Value (µF) Voltage (V) Tolerance ( %) R/S Part No. Material 4700 ±20 Radial Electrolytic ±20 Radial Electrolytic C3/4 ±20 Axial Electrolytic ±20 Radial Ceramic 0.0022 +80/-20 Radial Ceramic 0.022 +80/-20 Radial Ceramic ±20 Radial Electrolytic C9~12 0.022...
  • Page 27 RESISTORS Wattage Ref.No. Value (ohms) Tolerance ( %) R/S Part No. Material ±5 Carbon 3.9K ±5 Carbon 1.5K ±5 Carbon ±5 Carbon ±5 Carbon R6/7 ±5 Carbon R8/9 4.7K ±5 Carbon ±5 Carbon ±5 Carbon ±5 Carbon 8.2K ±5 Carbon 6.8K ±5 Carbon...
  • Page 28 Ref. No. Description R/S Part No. R/S Part No. Mfr’s Part No. SN74LS174N or (D-TYPE F.F) MOTOROLA MB74LS174M or FUJITSU HD74LS174P HITACHI µPD4016C-1 or (STATIC RAM) U9/10 µPD4016D-1 or MB8128-15P or FUJITSU MSM2128-20RS MC6847P (VDG) MOTOROLA SN74LS14N or (INVERTER) MOTOROLA MB74LS14M or FUJITSU HD74LS14P...
  • Page 29 EXPLODED VIEW PARTS LIST Ref. No. Description R/S Part No. R/S Part No. Mfr’s Part No. Cabinet Ass’y, Top M00324 Cabinet, Top 601210420A Plate, Model 711010040A Cover, Connector 851210720A Key Board Ass’y 187510010A Knob, Reset (Red) 659510310A Holder, SW Reset 411101870A Case, Shield 473010160A...

  • Page 30: Printed Circuit Boards

    SECTION VII PRINTED CIRCUIT BOARDS – 30 –...
  • Page 31 MAIN P.C.B. (TOP VIEW) – 31 –...
  • Page 32 (BOTTOM VIEW) – 32 –...

  • Page 33: Ic Internal Connections

    SECTION VIII IC INTERNAL CONNECTIONS – 33 –...
  • Page 34 IC INTERNAL CONNECTIONS MC6803G (Motorola) or HD6803P (Hitachi) – 34 –...
  • Page 35 MC6847P (Motorola) – 35 –...
  • Page 36 SN74LS373N (Motorola) or MB74LS373M (Fujitsu) SN74LS245N (Motorola) or MB74LS245M (Fujitsu) – 36 –...
  • Page 37 MB8364M (Fujitsu) U9/10 µPD4016C-1 (NEC) or µPD4016D-1 (NEC) or MB8128-15P (Fujitsu) or MSM2128-20RS (Oki) – 37 –...
  • Page 38 SN74LS155N (Motorola) or MB74LS155M (Fujitsu) or HD74LS155P (Hitachi) U5/6 SN74LS367AN (Motorola) or MB74LS367AM (Fujitsu) or HD74LS367AP (Hitachi) – 38 –...
  • Page 39 SN74LS174N (Motorola) or MB74LS174M (Fujitsu) or HD74LS174P (Hitachi) MC14503BCP (Motorola) or HD14503BP (Hitachi) or µPD4503BC (NEC) or MSM4503RS (Oki) SN74LS76AN (Motorola) or MB74LS76AM (Fujitsu) or HD74LS76P (Hitachi) – 39 –...
  • Page 40 SN74LS14N (Motorola) or MB74LS14M (Fujitsu) or HD74LS14P (Hitachi) SN74LS32N (Motorola) or MB74LS32M (Fujitsu) or HD74LS32P (Hitachi) SN74LS32N (Motorola) or MB74LS32M (Fujitsu) or HD74LS32P (Hitachi) – 40 –...
  • Page 41 LM339N (Motorola) or µPC339C (NEC) SN74LS74AN (Motorola) or MB74LS74AM (Fujitsu) or HD74LS74AP (Hitachi) – 41 –...
  • Page 42 MC1741CP1 (Motorola) or HA17741PS (Hitachi) MC7805CT (Motorola) or NJM7805A (JRC) or µPC7805H (NEC) – 42 –...

  • Page 43: Schematlc Dlagram

    SECTION IX SCHEMATlC DlAGRAM SECTION X EXPLODED VlEW – 43 –...
  • Page 44 RADIO SHACK, A DIVISION OF TANDY CORPORATION U.S.A.: FORT WORTH, TEXAS 76102 CANADA: BARRIE. ONTARIO L4M 4W5 TANDY CORPORATION AUSTRALIA BELGIUM U. K. 91 KURRAJONG ROAD PARC INDUSTRIEL DE NANINNE BILSTON ROAD WEONESBURY MOUNT ORUITT, N.S.W. 2770 5140 NANINNE WEST MIDLANDS WS10 7JN...

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