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Memotech Limited MTX 500 Service Manual

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MTX Service Manual

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  • Page 1 MTX Service Manual...
  • Page 2 MTX 500/512 SERVICE MANUAL & TECHNICAL INFORMATION Memotech Limited Witney Oxon OX8 6BX Tel: (0993) 2997 Tlx: UK83372 MEMTEC G MTX Service Manual...

  • Page 3: Table Of Contents

    CONTENTS Page Overall Description........1 Internal Expansions compatibility.....4 CPU..........6 Z80 Pin Description.........7 CTC..........10 Z80 CTC Pin Description......11 DART..........13 Z80 DART Pin Description......14 TMS 9929 VDP.........17 PAL VDP Horizontal Timing......18 9929 Signal Waveforms......19 MTX Series System Bus........20 System Block Diagram.......21 MTX Disassembly Instructions......22 Trouble Shooting Guide.......25...
  • Page 4 Timing Chain.........46 Rear Plastic moulding........48 PARTS LIST...........49 MTX500/512........50 PAL Video Board.......54 Keyboard/Keytops......56 Power Supply........59 Plastic Rear Panel......60 Packing........60 RS232 Board........62 32K Memory Expansion......64 Expansion.........65 Schematic Diagrams 4000-04........66 PAL Video Board.......68 NTSC Video Board......69 Memory Expansion Board......70 RS232 Communications Board....71 MTX Service Manual...

  • Page 5: Overall Description

    INTRODUCTION Overall Description The MTX Series personal computer systems are high performance 8-bit computers uniquely designed operate memory intensive ROM-based DISC- based environments. choice of Microprocessor the TMS 9929A series video processor as the key components of hardware architecture is consistent with a low cost ROM- based...
  • Page 6 CPU Board Mounted lower chassis, board accommodates: Z80A CPU operating at 4Mhz. 24K of ROM which contains: BASIC - incorporating sophisticated MTX LOGO-type graphics commands. MTX NODDY - Interactive screen manipulation routines. FRONT PANEL DISPLAY incorporating Assembler/Disassembler plus Z80 Register, Memory Program display and manipulation routines.
  • Page 7 Graphics Facilities Up to 32 independently controllable user definable sprites, plus pattern plane and backdrop plane. High level sprite-orientated graphics commands. Input/Output Provided as standard: 1. CASSETTE PORT (variable rate, up to 2 400 baud) 2. UNCOMMITTED PARALLEL INPUT/OUTPUT PORT 3.
  • Page 8 NODE/RING SYSTEM Communications software and interfacing enabling construction of MTX Ring Systems. The system interrupt driven and runs in conjunction with twin RS232 Communications Board. Compatibility of the memory boards and Communications Board is given below. Compatibility table of internal expansion boards RAM BOARDS 128k 256k...
  • Page 9 mouldings are incorporated in the PSU casing support the input and output cables. output cable terminates in a 240 degree, connector. The PSU is supplied as a sealed unit. MTX Service Manual...

  • Page 10: Z80 Cpu

    Z80 CPU The instruction set contains 158 instructions. instructions of the 8080A are included as subset; 8080A software compatibility is maintained. Eight MHz, 6 MHz, 4MHz and 2.5 MHz clocks for the Z80H, Z80B, Z80A and Z80 CPU result in rapid instruction execution with consequent high data throughput.
  • Page 11 Pin description A0-A15. Address Bus (output, active High,·3-state). form a 16-bit address bus. Address provides the address for memory data bus exchanges (up to 64K bytes) and for I/O device exchanges. BUSACK. Acknowledge (output, active Low). Acknowledge indicates to the requesting device that...
  • Page 12 IORQ. Input/Output Request (output, active Low, state). IORQ indicates that the lower half of the address bus holds a valid I/O address for an read or write operation. IORQ is also generated concurrently with during interrupt acknowledge cycle to indicate that interrupt response vector can be placed on the data bus.
  • Page 13 RFSH. Refresh (output, active Low). RFSH, together with MREQ, indicates that the lower seven bits of system's address bus can be used refresh address to the system's dynamic memories. WAIT. Wait (input, active Low). WAIT indicates to that the addressed memory or I/O devices not ready for a data transfer.

  • Page 14: Z80 Ctc

    Z80 CTC Z-80 four-channel counter/timer programmed system software for a broad range counting timing applications. four independently programmable channels of the Z-80 satisfy common microcomputer system requirements event counting, interrupt and interval timing, general clock rate generation. System design is simplified because the connects directly to both the Z-80 CPU and the Z-80 SIO with additional logic.
  • Page 15 Pin Description Chip Enable (input, active Low). When enabled the accepts control words, interrupt vectors, time constant data words from the data bus during I/O write cycle; or transmits the contents down-counter to the CPU during an read cycle. most applications this signal...
  • Page 16 INT. Interrupt Request (output, open drain, active Low). Low when any Z-80 CTC channel that has been programmed to enable interrupts has a zero-count condition in its down-counter. IORQ. Input/Output Request (input from CPU, active Low). Used with CE and RD to transfer data and channel control words between the Z-80 CPU and...

  • Page 17: Z80 Dart

    Z80 DART Z-80 DART (Dual-Channel Asynchronous Receiver/Transmitter) is a dual-channel multi-function peripheral component that satisfies a wide variety asynchronous serial data communications requirements in micro-computer systems. The Z-80 DART is used serial-to-parallel, parallel-to-serial converter controller in asynchronous applications. addition, device also provides modem...
  • Page 18 Pin Description B/A. Channel A Or B Select (input, High selects channel This input defines which channel is accessed during a data transfer between the CPU and the 80 DART. C/D. Control Data Select (input, High selects Control). This input specifies type information...
  • Page 19 IEI. Interrupt Enable In (input, active High) is used with IEO to form a priority daisy chain when there is more than one interrupt-driven device. High this line indicates that no other device higher priority being serviced interrupt service routine. IEO.
  • Page 20 RxDA, RxDB. Receive Data (inputs, active High). RESET. Reset (input, active Low). Disables both receivers and transmitters, forces TxDA and TxDB marking, forces modem controls High disables all interrupts. RIA, RIB. Ring Indicator (inputs, Active Low). These inputs are similar to CTS and DCD. The Z-80 DART detects both logic level transitions and...

  • Page 21: Tms 9929 Vdp

    TMS 9929 VDP (Video Display Processor) Introduction This Preliminary Specification of the TMS 9929 is to be considered "ADD ON" to basic 9918 specification. The TMS 9929 is effectively identical TMS 9918 functionally and only has color video section that is different. TMS 9918 provides a composite color video signal...
  • Page 22 4116 VRAM PIN NAMES A0-A6 Address Inputs Column Address Strobe Data Input Data Output Row Address Strobe WRITE Read/Write Input -5V Power Supply +5V Power Supply +12V Power Supply Ground MTX Service Manual...
  • Page 23 MTX Service Manual...

  • Page 24: Mtx Series System Bus

    MTX SERIES BUS system Bus comprises the full Z80 bus, power supply rails, ROMpak enable (GROM), ROM page ports R2, RAM page ports P0 to P3 and serial clock lines 01 and 02. All lines are externally available on J1, which is a 60 way (30 + 30) 0.1"...

  • Page 25: System Block Diagram

    System Block Diagram MTX Service Manual...
  • Page 26 DISASSEMBLY INSTRUCTIONS Using an Allen key, remove the three dome head screws from the right & left hand ends MTX. Lift the MTX keyboard at the rear just above plastic panel. careful not damage keyboard interconnecting cable. Gently ease the KBD (keyboard) interconnecting cable from the mother board and slide the top KBD...
  • Page 27 under side of the MTX reveals a single screw which secures the MTX mother board to bottom chassis. By removing the main screw and earth strap Mother Board and Rear Plug panel will slide from the case bottom. Faults rarely complained about nonetheless faults, include I/O ports that are insecurely...
  • Page 28 MTX Service Manual...

  • Page 29: Trouble Shooting Guide

    Introduction To Trouble Shooting Guide Memotech products are all given a vigorous series tests before despatch to the end user. These tests include:- Loading and saving functions, sound channel checks, compatibility with printers and other add ons, etc. Once the units have passed this stage tests...

  • Page 30: Symptom 1

    SYMPTOM 1 power up:- No display or only a black white display. Cause of Trouble Black and White output. Check Point Video Board Oscillation of Xtal 4.433619Mhz or pin 17 of LM1889 IC47. Repair Method If pulse is present on P17 of LM1889 turn until oscillation is at its optimum...
  • Page 31 If still faulty replace the Modulator. Cause of Trouble No video output, i.e. 'fuzzy screen' Check Point Pal board J11 and or Modulator Repair Method Check pulse on pin 3 of J11 or Pin Modulator. Check for short to 5v...or replace Modulator. Check +12v - if absent replace 12v Regulator.

  • Page 32: Symptom 2

    SYMPTOM 2 When power is switched on: Blank screen - no humming sound. Cause of Trouble Faulty video board Check Point Check to see if you have control G note Repair Method control G note is present video board faulty-Replace video board. Cause of Trouble Blank screen with no control G sound Check Point...
  • Page 33 Repair Method pulse absent on 4Mhz Xtal follow associated circuitry until fault is apparent. If RESET is held low- follow associated circuitry until fault apparent. Also - see page 33. Cause of Trouble Blank screen with no control G sound Check Point above checks are o.k.

  • Page 34: Symptom 3

    SYMPTOM 3 Corrupt video display or characters Cause of Trouble - 5v absent Check Point absent - check for short (monitor o/p) of video board - or repair open circuit. The -5v is generally shorted to 0v this point. Cause of Trouble Faulty Video Ram Check Point Check for pulse on pin 2 of Video Ram.
  • Page 35 may pick out the faulty component. Cause of Trouble Faulty TMS 9929 Check Point Check pins 3 to 10 and pins 25 to 32 Repair Method signal is absent replace 9929 video processor. WARNING:When you earth the Video Rams - make sure earth them via a 10 OHM - 15 OHM Resistor.
  • Page 36 Cause of Trouble Faulty Bridge Rectifier Check Point Check your +5v and +12v Repair Method If signal is poor trace fault from either 7805 or 7812 Regulators to faulty component. SYMPTOM 5 When power is switched on:- Green screen humming noise.
  • Page 37 Cause of Trouble Faulty voltages Check Point Check all your voltages 0v, 5v, 12v, -5v, -12v Repair Method signal absent follow offending circuitry from source and repair. Cause of Trouble Faulty RESET circuit - also see page 29. Check Point Check Points are:- Pin 3 of IC18 BCN4070 CMOS Pin 26 of C.P.U.
  • Page 38 Repair Method address signal is absent - Reset whilst probing. If signal is still absent start by replacing C.P.U. Check both 74LS157's (PCB Location 6C and to see if they are multiplexing. If 74LS157 pin 1 pulse is absent, check pin PAL14L4 and follow circuitry through pins...
  • Page 39 find it helpful to replace all socketed IC's with a known good set before attempting rectify this fault. fact that a signal is absent from the system data bus does not necessarily mean that there fault in Ram. very difficult determine Ram faults with an oscilloscope alone.
  • Page 40 Check Point typing LO."" (RET) and loading long playing cassette tape start probing at J2 CSST out. Repair Method easily follow the signals from through opamp 314. (Remember 6 is normally -12v) and in to 4070 CMOS out at 4. - Replace faulty component. If no fault found change CPU or CTC.
  • Page 41 Cause of Trouble MTX 512 with internal expansions only Check Point Check right hand bus connector Repair Method Either make sure the bus connector clean or...ideally hard solder the expansion board to the mother board. Before these tests are carried out always check that you have a good tape recorder that is at the correct volume (between level 7 and 10).
  • Page 42 pulse is present on both 4E (374) (SN76489AN) check for pulse on pin 1 of J13 board and pin 3 of J11 on pal board. either absent check for open circuit replace pal board. pulse is present on J11 and J13 check tuning of modulator.
  • Page 43 Repair Method Generally key bounce is caused by faulty key board switches. Simply de-solder replace offending key(s). Cause of Trouble Key(s) u/s Check Point J1-keyboard interconnection header plug Repair Method Check that the keyboard interconnection cable is secure and not torn. Check that the offending keys work by buzzing...
  • Page 44 SYMPTOM 9 faults - e.g. Memory expansions, boards, RS232, Printers etc. Cause of Trouble Memory upgrade not obtaining Ram top Check Point Check for correct prom coding, see page 45, check rams in sockets (if any) for poor connection Repair Method prom o.k.
  • Page 45 Check links 6 and 7 on MTX. Look closely at the 273 (5A) on mother board and associated circuitry. Cause of Trouble RS232 Check Points As above. Repair Methods As above -> If intermittent fire up modify timing chain -> see page 46.
  • Page 46 Further information on the UM 1286 Modulator. The Pal-Modulator is used to encode the R-Y, B-Y and signals from the MTX home computer and to modulate them together with the sound signal to high frequency (591.250 MHz). R-Y and B-Y are called the Chrominance signals. the information about the brightness is in signal called the Luminance signal.
  • Page 47 Test and setting procedure of UM 1286 and video board sure that your TV set, MTX computer other test equipment is switched on at least half an hour before beginning the test. Connect MTX computer to the TV aerial cable. Set the TV set to channel 36 of the 1V band (UHF) obtain...
  • Page 48 MTX 500 4000/04 with 32k L Ram chips |--BLUE PAL 212 FUSES BLOWN MTX 500 4000/05 with 32k H Ram chips. Links 6 and 7 as point 1. |-WHITE PAL MTX 500 4000/05 with 32k L Ram chips. Links 6 and | 194 FUSES 7 as point 2.
  • Page 49 PROM CODE FOR MEMORY EXPANSION BOARDS MTX 500 CODE DESCRIPTION 1 ROW OF 32K L OR (MAX 96K) 2 ROWS OF 32K L 1 ROW OF 32K L (MAX 96K) 1 ROW OF 32K L AND 1 ROW OF 32K H...
  • Page 50 Timing chain modification October 1984 Memotech altered timing chain circuitry due to occasional faults occurring after about 2 hours of use - and poor fire up response. (esp; when running in conjunction with F.D.X.) have since up-dated all our units incorporate this 'modification'.
  • Page 51 MTX Service Manual...
  • Page 52 Plastic back panel. You will find that your TV/Monitor picture will tear or wobble if your plastic back panel does not have: Earth straps 47pf capacitor Illustration of assembly of power transistor. MTX Service Manual...
  • Page 53 PARTS LIST FOR THE: MTX 512 04 RS232 I/F 32K MEMORY EXPANSION ROM EXPANSION MTX Service Manual...
  • Page 54 MTX LOADING STAGE 1. MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ CONS CNOND9P 9 Way Canon D Type J4,J5 HS01 Heat Sink HS01 INSU BUSH Insulating Bush INSU PAD Insulating Pad M3HEXH M3 Hex Nut Q4,RG1,RG2 M3HEXN M3 Nylon Nut...
  • Page 55 CAPC NF0047 47pf Ceramic Disc Cap CAPE A470016 4700uf 16v Axial Cap CAPE R001016 10uf 16v Radial Cap C11,C38-C40, C49,C57 CAPE R010025 100uf 25v Radial Cap CAPE R470016 4700uf 16v Radial Cap 10mm 1 CAPP NF0100 100nf Polyester Cap C17,C52,C54,C55, C58-C61 CAPS NF0047 47nf Sibitat Cap...
  • Page 56 CRXL 4.000 4.000 MHz Crystal XTAL1 DODE IN4004 IN4004 Silicon Diode D14,D16,D18,D19 DODE IN4148 IN4148 Silicon Diode D1-D11,D13 DODE IN5402 IN5402 Silicon Diode D15,D17 DODE Z4V7 4V7 Zener Diode DODE Z5V1 5V1 Zener Diode DODE Z5V6 5V6 Zener Diode Ferrite Bead LK10,LK11 FUSE HLD5229 20mm Fuse holder PC MT...

  • Page 57: Um1286 Modulator

    MDOR UM1286 UM1286 Modulator MODULATOR 033R 33 OHM 1/4W C/FILM RES 330R 330 OHM 1/4W C/FILM RES R14,R15 560R 560 OHM 1/4W C/FILM RES R34,R40 K001 1K OHM 1/4W C/FILM RES R10,R11,R19,R20, R21,R60 K002.2 2K2 OHM 1/4W C/FILM RES K003.3 3K3 OHM 1/4W C/FILM RES R32,R33 K004.7...
  • Page 58 ICMO Z80ACTC Z80A CTC ICPA 14L4 PAL 14L4-2CN ICRO 38128A ROM 16B MSM38128A IC46 ICRO 3864 ROM 8B MSM3864 IC45 MTX PAL VIDEO BOARD MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ PF0033 33pf Ceramic Plate Cap C45,C46,C50 PF0039 39pf Ceramic Plate Cap...
  • Page 59 ICMO LM1889 LM1889 IDTA UH004.7 4.7UH Axial Inductor IDTA UH022 22UH Axial Inductor IDTA UH033 33UH Axial Inductor IDTA UH100 100UH Axial Inductor 440HEXN 440 Nylon Nut PAL BOARD SUPPORT MTX PAL VIDEO Board 220R 220 OHM 1/4W C/FILM RES 330R 330 OHM 1/4W C/FILM RES R45,R47,R54...

  • Page 60: Boards

    MTX KEYBOARD MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ CONL WIRE Wire Link 39/24 SWG CONP HSILR20 20 Way SIL R/A Header CONS SIL20AS 20 Way SIL KBD Assembly KBNT PNLMTX KBD Switch Mounting Plate MKBD104 KBD 01-04 PCB ML-3-CM...
  • Page 61 KYTP 6011F & - 6 KYTP 6153F 6 - DEL KYTP 7011F ´ - 7 KYTP 7163F 7 - PAGE KYTP 8011F ( - 8 KYTP 8163F 8 - EOL KYTP 9012F ) - 9 KYTP 9163F 9 - BRK KYTP A000F KYTP A0033F ALPHA LOCK...
  • Page 62 KYTP F663F KYTP F664F KYTP F665F KYTP F666F KYTP F667F KYTP F668F KYTP FF00F * - : KYTP G000F KYTP GG00F ? - / KYTP H000F KYTP HH000F KYTP HH05F = - - KYTP I000F KYTP J000F KYTP JJ00F { - [ KYTP JJ03F } - ] KYTP K000F...
  • Page 63 KYTP Q000F KYTP R000F KYTP R031F KYTP S000F KYTP S020F SHIFT KYTP SPACBRF SPACE BAR KYTP T000F KYTP U000F KYTP V000F KYTP W000F KYTP X000F KYTP Y000F KYTP Z000F GT8C SPACE BAR KIT MTX POWER SUPPLY UNIT MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO.

  • Page 64: Moulding

    MTX REAR PLUG ASSEMBLY MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ PF0047 47pf Ceramic Plate Cap CONP EYE4BA 4BA Crimped Eyelets CONP BNCONT BNC Chassis MT Socket CONP HIFIC Phono Socket Nut Fixing CONS SIL04AS 4 Way Cable ASSY FACC WIR.5B .5mm Black Wire...
  • Page 65 MTX512 MTX 512 Box CONP J23.5 23.5 Cable Jack Plug CONP PNOCAX Phono to Coax Cable GUAR 512UK 512 UK Guarantee Card MTXCVR Plastic Cartridge Cover MTX512 MTX 512 Polypack STNP 029 MTX Series Manual STNP 078 MTX 512 Serial No. Label STNP 236 MTX Series Brochure NPTE MTX512...
  • Page 66 MTX RS232 I/F MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ PF560 560pf Ceramic Plate Cap C1,C2,C12,C13 CAPE R001016 10uf 16v Radial Cap C3,C4 CAPS NF0047 47nf Sibitat Cap C5-C11 CONL SHUNT02 2 Way Shunt (Jumper) CONP HSIL13 13 Way SIL Header CONS EDGE60...
  • Page 67 RS232 I/F TESTING MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ 75188 SN75188N IC13 75189 SN75189N IC12,IC14 Z80DART Z80A DART ICPA 14L4 PAL 14L4-2CN RS232 I/F PACKING MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------...
  • Page 68 32K MEMORY EXPANSION MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ PF0047 47pf Ceramic Plate Cap PF0068 68pf Ceramic Plate Cap CAPS NF0047 47nf Sibitat Cap C1-C5,C15-C22 CONL WIRE Wire Link CONS EDGE60 30+30 Way Connector CONS DIL16 16 Pin DIL Socket IC15-IC22...
  • Page 69 ALLK2MM 2MM Allen Key ROM EXPANSION MEMOTECH ITEM DESCRIPTION NO./ PCB COMPONENT LOCATION PART NO. UNIT / COMMENTS ------------------------------------------------------------------------ CAPS NF0047 47nf Sibitat Cap C1-C7 CONP HSIL03 3 Way SIL Header LK2,LK3 CONL SHUNT02 2 Way Shunt (Jumper) Lo,Lo CONL WIRE Wire Link 39/24 SWG 41,51,61,71,16 CONS DIL20...
  • Page 70 MTX Service Manual...
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  • Page 75: Board

    RING SYSTEM The MTX ring uses channel A of the dart. If the ring is installed, the baud command must not be used for either channel as the dart is initialised differently for the ring. Channel B is not used by the ring and is available as serial I/O port.
  • Page 76 MTX Service Manual...
  • Page 77 This manual was brought to you by ROBCFG MTX Service Manual...
  • Page 78 MTX Service Manual...

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