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Radio Shack TRS-80 Service Manual

Summary of 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 26-3011.

  • Page 2: Table of Contents

    – 2 – table of contents section page number number i system description - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3 ii specifications - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 7 iii disassembly ...

  • Page 3: Section  I

    – 3 – section i system description.

  • Page 4

    – 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 l...

  • Page 5

    – 5 – system block diagram.

  • Page 6

    – 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 ram control register 0013 not used 0012 not used 0011 not used 0...

  • Page 7: Section  Ii

    – 7 – section ii specifications.

  • Page 8

    – 8 – specifications power supply ac/ac adaptor input 120v/60hz output 8.0v/1.5a 16w rf modulator ch. Fc (mhz) fsc (mhz) for u.S.A./canada 3 61.25 +/-0.25 4.5 +/-0.2 4 67.65 4.5 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-...

  • Page 9: Section  Iii

    – 9 – section iii disassembly / reassembly.

  • Page 10

    – 10 – disassembly 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. 3. Turn the comp...

  • Page 11: Section  Iv

    – 11 – section iv theory of operation.

  • Page 12

    – 12 – cpu-6803 the main component of this microcomputer system is the 6803 cpu. This is a 40-pin in- tegrated circuit which provides the address, data, and miscellaneous control signals. The cpu receives the main clock frequency of 3.579545 mhz from the modulator assembly and divides this by 4 to p...

  • Page 13

    – 13 – detailed tape format information tor equal to 1/2 volt. Since the other input is biased at 1 volt, the comparator output is switched to the high state. If the ac input from the recorder is positive, diode d6 is turned off and the input to the comparator will be at some point greater than 1 vo...

  • Page 14

    – 14 – rs-232c interface the rs-232c interface utilizes a 4-pin din con- nector (j2). This interface allows the computer to have serial communication with printers, modem, or other computers. The four signals used by the interface are: 1. Cd — a status input line 2. Rs232ln — serial data input 3. Gr...

  • Page 15

    – 15 – i/o connector table 1. I/o connector signals pin signal name description 1 gnd signal ground 2 gnd signal ground 3 d0 cpu data bit 0 4 d1 cpu data bit 1 5 d2 cpu data bit 2 6 d3 cpu data bit 3 7 d4 cpu data bit 4 8 d5 cpu data bit 5 9 d6 cpu data bit 6 10 d7 cpu data bit 7 11 r/w cpu read/wri...

  • Page 16

    – 16 – keyboard interface tv switch box figure 4. Antenna switch box schematic to read the keyboard, only one column is enabled by writing a zero to one of the eight cpu i/o lines that corresponds to that column, and by writing ones to all the other lines. If a key has been pressed in that column, o...

  • Page 17

    – 17 – power supply the mc-10 power supply utilizes an external power pack to supply 8 vac at 1.5 amps. This input ac voltage is connected through the power switch to the bridge rectifier. The mc-10 operates primarily on +5 volts, so the negative output of the bridge is grounded to provide a larger ...

  • Page 18

    – 18 – table 2. Vdg control register table 3 table 4. Available characters (00 - 7f) control register bits dma bits mode selected d6 d5 d4 d3 d2 d6 d7 css a*/g gmd gm1 gm2 (int*/ext) inv a*/s 0 0 x x 0 0 0 alphanumerical green 0 0 x x 0 1 0 alphanumerical inverted green 1 0 x x 0 0 0 alphanumerical ...

  • Page 19

    – 19 – device selection system timing figure 5 allows an external device to change the mc-10 memory map. Also, the disable signal for the memory write is ored with a12 to prevent a complete overlap of the 4k of ram into the 16k memory map segment. From the output of the 74ls155 the iy1 output is use...

  • Page 20

    – 20 – the mc6847 (vdg) has access to the ram dur- ing the low portion of the e clock. Also during the low portion of e, the signal as is used to latch the address lines in the latch (u2). During the high portion of e, all cpu address and data lines are valid and any accesses to the ram or rom occur...

  • Page 21: Section  V

    – 21 – section v troubleshooting.

  • Page 22

    – 22 – troubleshooting problems with the mc-10 may be separated into two major areas - i/o problems and dead com- puter problems. If the computer will display the sign-on message, then a fairly simple set of testing procedures may be used to isolate the problem. If, however, the computer displays ra...

  • Page 23

    – 23 – rs-232 interface the rs-232 interface uses three simple level converter circuits. Isolating the problem will be an easy job of comparing the input to the out- put. Connect a din-type plug to the serial i/o jack to short together pins 1, 2, and 4. Now, type in the following test program: 5 pok...

  • Page 24

    – 24 – adjustment of vsb (vestigial side band) filter make connection according to figure 7 figure 7 1. Adjust marker of tracking generator at 61.25 mhz (marker - 2) 2. Adjust l102 so lower side band peak point meets 61.25 mhz (marker - 2) 3. Adjust marker of tracking generator at 72.15 mhz (marker ...

  • Page 25: Section  Vi

    – 25 – section vi parts list.

  • Page 26

    – 26 – printed circuit board parts capacitors diodes core connectors ref.No. Value ( µ f) voltage (v) tolerance ( %) r/s part no. Material c1 4700 16 ±20 radial electrolytic c2 10 25 ±20 radial electrolytic c3/4 100 16 ±20 axial electrolytic c5 0.1 25 ±20 radial ceramic c6 0.0022 50 +80/-20 radial c...

  • Page 27

    – 27 – resistors switches integrated circuits ref.No. Value (ohms) wattage tolerance ( %) r/s part no. Material r1 100 1/2 ±5 carbon r2 3.9k 1/6 ±5 carbon r3 1.5k 1/6 ±5 carbon r4 10k 1/4 ±5 carbon r5 15k 1/4 ±5 carbon r6/7 10k 1/4 ±5 carbon r8/9 4.7k 1/4 ±5 carbon r10 75k 1/6 ±5 carbon r11 24k 1/6 ...

  • Page 28

    – 28 – ref. No. Description r/s part no. R/s part no. Mfr’s part no. U8 sn74ls174n or (d-type f.F) mb74ls174m or hd74ls174p motorola fujitsu hitachi u9/10 µ pd4016c-1 or (static ram) µ pd4016d-1 or mb8128-15p or msm2128-20rs nec nec fujitsu oki u11 mc6847p (vdg) motorola u12 sn74ls14n or (inverter) ...

  • Page 29

    – 29 – exploded view parts list miscellaneous parts list ref. No. Description r/s part no. R/s part no. Mfr’s part no. 1 cabinet ass’y, top cabinet, top plate, model m00324 601210420a 711010040a 2 cover, connector 851210720a 3 key board ass’y 187510010a 4 knob, reset (red) 659510310a 5 holder, sw re...

  • Page 30: Section  Vii

    – 30 – section vii printed circuit boards.

  • Page 31

    – 31 – main p.C.B. (top view).

  • Page 32

    – 32 – (bottom view).

  • Page 33: Section  Viii

    – 33 – section viii ic internal connections.

  • Page 34

    – 34 – ic internal connections u1 mc6803g (motorola) or hd6803p (hitachi).

  • Page 35

    – 35 – u11 mc6847p (motorola).

  • Page 36

    – 36 – u2 sn74ls373n (motorola) or mb74ls373m (fujitsu) u7 sn74ls245n (motorola) or mb74ls245m (fujitsu).

  • Page 37

    – 37 – u3 mb8364m (fujitsu) u9/10 µ pd4016c-1 (nec) or µ pd4016d-1 (nec) or mb8128-15p (fujitsu) or msm2128-20rs (oki).

  • Page 38

    – 38 – u4 sn74ls155n (motorola) or mb74ls155m (fujitsu) or hd74ls155p (hitachi) u5/6 sn74ls367an (motorola) or mb74ls367am (fujitsu) or hd74ls367ap (hitachi).

  • Page 39

    – 39 – u8 sn74ls174n (motorola) or mb74ls174m (fujitsu) or hd74ls174p (hitachi) u14 mc14503bcp (motorola) or hd14503bp (hitachi) or µ pd4503bc (nec) or msm4503rs (oki) u19 sn74ls76an (motorola) or mb74ls76am (fujitsu) or hd74ls76p (hitachi).

  • Page 40

    – 40 – u12 sn74ls14n (motorola) or mb74ls14m (fujitsu) or hd74ls14p (hitachi) u13 sn74ls32n (motorola) or mb74ls32m (fujitsu) or hd74ls32p (hitachi) u20 sn74ls32n (motorola) or mb74ls32m (fujitsu) or hd74ls32p (hitachi).

  • Page 41

    – 41 – u15 lm339n (motorola) or µ pc339c (nec) u18 sn74ls74an (motorola) or mb74ls74am (fujitsu) or hd74ls74ap (hitachi).

  • Page 42

    – 42 – u16 mc1741cp1 (motorola) or ha17741ps (hitachi) u17 mc7805ct (motorola) or njm7805a (jrc) or µ pc7805h (nec).

  • Page 43: Section  Ix

    – 43 – section ix schematlc dlagram section x exploded vlew.

  • Page 44

    Radio shack, a division of tandy corporation u.S.A.: fort worth, texas 76102 canada: barrie. Ontario l4m 4w5 tandy corporation 6a3 printed in u.S.A. 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 ...