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Memotech Limited MTX 500, Service Manual

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Memotech Limited MTX 500 Service Manual Download Page 34

      30

      SYMPTOM 3

           Corrupt video display or characters

      a)

      Cause of Trouble
           
           - 5v absent

      Check Point

           1  If  -5v  is  absent - check for  short  at  J12
              (monitor  o/p) of video board - or repair  open
              circuit. The -5v is generally shorted to 0v  at
              this point.

      b)

      Cause of Trouble

           Faulty Video Ram

      Check Point

           Check for pulse on pin 2 of Video Ram.
           Check for signal on P14 of any Video Ram.

      Repair Method

           1  Systematically   disable  the  Video  Rams   by
              earthing  pin  14. Continue with  this  process
              until   corruption   has   reduced.    The   IC
              with  the  least corruption  when  earthing, is
              likely to be faulty...replace.   See warning on
              page 31.

           2  If  the corruption is very bad scopeing pin  14

MTX Service Manual

Summary of Contents for MTX 500

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: ...ctions 22 Trouble Shooting Guide 25 Symptom 1 No Display Black and white display 26 Symptom 2 Blank screen no humming power on 28 Symptom 3 Corrupt Video Display or characters 30 Symptom 4 Bad hum bar...

Page 4: ...oard 54 Keyboard Keytops 56 Power Supply 59 Plastic Rear Panel 60 Packing 60 RS232 Board 62 32K Memory Expansion 64 ROM Expansion 65 Schematic Diagrams MTX 4000 04 66 PAL Video Board 68 NTSC Video Boa...

Page 5: ...a separate 16K Byte dedicated video memory A 24K Byte ROM contains MTX BASIC the systems monitor supplementary languages and utilities The standard interfaces included are tape cassette Read Write to...

Page 6: ...s constant under all display formats VIDEO BOARD for television and sound signal encoding REAL TIME CLOCK CHARACTER SETS Numeric upper case lower case user definable characters and user definable spri...

Page 7: ...ideo signal 1V peak to peak CARTRIDGE PORT 6 PARALLEL PRINTER PORT compatible with Centronics type printers Expansions Up to two expansion boards may be added internally These may be Memory RAM Boards...

Page 8: ...e bus these provide MTX PASCAL NODE SYSTEM software Business Education and Games software Suitable Printers Centronics type parallel printers RS232 serial printers requires Communications Board Power...

Page 9: ...uldings are incorporated in the PSU casing to support the input and output cables The output cable terminates in a 240 degree six pin DIN connector The PSU is supplied as a sealed unit MTX Service Man...

Page 10: ...ors and associated family of peripheral controllers are linked by a vectored interrupt system This system may be daisy chained to allow implementation of a priority interrupt scheme Little if any addi...

Page 11: ...ontrol these lines BUSREQ is normally wire ORed and requires an external pull up for these applications Extended BUSREQ periods due to extensive DMA operations can prevent the CPU from properly refres...

Page 12: ...able Interrupt input negative edge triggered NMI has a higher priority than INT NMI is always recognized at the end of the current instruction independent of the status of the interrupt enable flip fl...

Page 13: ...WAIT indicates to the CPU that the addressed memory or I O devices are not ready for a data transfer The CPU continues to enter a Wait state as long as this signal is active Extended WAIT periods can...

Page 14: ...s decoders and buffers may be required Programming the CTC is straightforward each channel is programmed with two bytes a third is necessary when interrupts are enabled Once started the CTC counts dow...

Page 15: ...TC channels In counter mode every active edge on this pin decrements the down counter In timer mode an active edge starts the timer CS0 CS1 Channel Select inputs active High Two bit binary address cod...

Page 16: ...errupt vector on the Z SO data bus M1 Machine Cycle One input from CPU active Low When M1 and IORQ are active the Z 80 CPU is acknowledging an interrupt The Z 80 CTC then places an interrupt vector on...

Page 17: ...nverter controller in asynchronous applications In addition the device also provides modem controls for both channels In applications where modem controls are not needed these lines can be used for ge...

Page 18: ...ize internal signals CTSA CTSB Clear To Send inputs active Low When programmed as Auto Enables a Low on these inputs enables the respective transmitter If not programmed as Auto Enables these inputs m...

Page 19: ...active the Z 80 CPU is fetching an instruction from memory when M1 is active while IORQ is active the Z 80 DART accepts M1 and IORQ as an interrupt acknowledge if the Z 80 DART is the highest priorit...

Page 20: ...transmitter empties TxCA TxCB Transmitter Clocks inputs TxD changes on the falling edge of TxC The Transmitter Clocks may be 1 16 32 or 64 times the data rate however the clock multiplier for the tran...

Page 21: ...nd Y respectively The two color difference signals are used then by an external quadrature modulator video encoder It is outside the Video Display Processor that the composite color video signal is ge...

Page 22: ...S A0 A6 Address Inputs CAS Column Address Strobe DIN Data Input DOUT Data Output RAS Row Address Strobe WRITE Read Write Input VBB 5V Power Supply VCC 5V Power Supply VDD 12V Power Supply VSS Ground 1...

Page 23: ...19 MTX Service Manual...

Page 24: ...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 card edge plug or internally on J0 which is also a 0 1 60 way card edge plug N...

Page 25: ...21 System Block Diagram MTX Service Manual...

Page 26: ...e rear just above the plastic panel Be careful not to damage the keyboard interconnecting cable 3 Gently ease the KBD keyboard interconnecting cable from the mother board and slide the top KBD to the...

Page 27: ...P C B i e Power Supply socket Printer port cassette ear and mic and joy stick ports Any competent initial check of a returned MTX should include these ports It should also include checking for the ny...

Page 28: ...24 MTX Service Manual...

Page 29: ...component that is faulty is generally weeded out at this stage The units are then given a final check over before they are packed and despatched to the end user Occasionally you may find less serious...

Page 30: ...of LM1889 turn CVI until oscillation is at its optimum pitch 3v peek to peek See fig no 1 2 If pulse is absent LM1889 is faulty or associated circuitry b Cause of Trouble Rapid Fading of colours Chec...

Page 31: ...Modulator 3 Check 12v if absent replace 12v Regulator d Cause of Trouble Monitor display faulty Check Point Pal board monitor connection cable Repair Method 1 Check for pulse on Q6 2N3906 transistor i...

Page 32: ...is faulty Replace video board b Cause of Trouble Blank screen with no control G sound Check Point Check 5v 5v 12v 0v Repair Method 1 If the 5 voltage is absent 2nd stage fuse has blown 2 If 12v and 5v...

Page 33: ...een with no control G sound Check Point If above checks are o k check the 10 6875 hz Xtal Repair Method 1 If pulse is absent Xtal is likely to be faulty 2 If pulse is present the TMS 9929 video proces...

Page 34: ...nt b Cause of Trouble Faulty Video Ram Check Point Check for pulse on pin 2 of Video Ram Check for signal on P14 of any Video Ram Repair Method 1 Systematically disable the Video Rams by earthing pin...

Page 35: ...rth the Video Rams make sure you earth them via a 10 OHM 15 OHM Resistor Do not earth them directly as this may damage the components SYMPTOM 4 When power is switched on Very bad hum bars causing corr...

Page 36: ...faulty components Since all the MTX s are thoroughly tested before despatch faults occurring such as green screen and humming after despatch are more than likely going to be component break down The b...

Page 37: ...Check Point Check Points are Pin 3 of IC18 BCN4070 CMOS Pin 26 of C P U Pin 34 of V D P 1 If signal is low trace fault back from Pin 3 of IC18 4070CMOS pay particular attention to C11 10uf cap 2 If s...

Page 38: ...e multiplexing 3 If 74LS157 pin 1 pulse is absent check pin 14 of PAL14L4 and follow circuitry through pins 3 4 5 and 6 of the 74LS04 PCB Location 2B to REF points MPX faulty d Cause of Trouble Faulty...

Page 39: ...ifficult to determine Ram faults with an oscilloscope alone You really do need the Memotech Ram Rig Tester SYMPTOM 6 Problems with the load and saving functions a Cause of Trouble Faulty jack socket C...

Page 40: ...from J2 through opamp 10E 314 Remember pin 6 is normally 12v and in to 4070 CMOS out at pin 4 Replace faulty component 2 If no fault found change CPU or CTC c Cause of Trouble Incorrect PAL14L4 value...

Page 41: ...level 7 and 10 Check your cassette leads remember ear to ear and mic to mic Check that the cassette tape itself is working and not damaged SYMPTOM 7 Problems with sound Depress control key and G key...

Page 42: ...SN76489AN or 74LS374N Check Point As above Repair Method 1 Often the sound channels become distorted once the components have reached their optimum temperature You can heat the SN76489AN and 74LS374N...

Page 43: ...able is secure and not torn 2 Check that the offending keys work by buzzing across the terminals whilst depressing the switch 3 Check for pulses on diodes DR0 DR7 4148 Anode 74LS273N 3A LCD lines c Ca...

Page 44: ...that both edge connector and upgrade connector is clean 2 Check links on the upgrade are correctly soldered in the LO position 3 R1 330 OHM 4 R2 680 OHM 5 If green screen fault refer to Rig Ram Test...

Page 45: ...mittent fire up modify timing chain see page 46 d Cause of Trouble Printer Check Point J6 Printer o p Repair Method 1 Be sure that the fault is not the printer itself or the interface cable 2 STROBE s...

Page 46: ...n the Y signal called the Luminance signal The Pal Encoder is built up around the LM 1889 and the UM1286 The LM 1889 integrated circuit receives the R Y and B Y signals from the video processor and pr...

Page 47: ...ator to set it 5 The video carrier is now set by 2 resistors running in series at RV1 a 10K OHM and 1K OHM These resistors can be replaced with a 1K MHz variable resistor 6 The two brass screws in the...

Page 48: ...s 6 and 7 as point 1 WHITE PAL 4 MTX 500 4000 05 with 32k L Ram chips Links 6 and 194 FUSES 7 as point 2 BLOWN _ 5 MTX 512 4000 04 64k _ YELLOW PAL 212 FUSES BLOWN _ _ 6 MTX 512 4000 05 Links 6 and 7...

Page 49: ...288K 2 ROWS OF 64K 08128 TO RUN IN CONJUNCTION WITH 00128 AND 04128 MAX 416K 2 ROWS 64K MTX 512 CODE DESCRIPTION 1LL 1 ROW OF 32K L OR MAX 128K 2 ROWS OF 32K L 1LH 1 ROW OF 32K L MAX 128K 1 ROW OF 32K...

Page 50: ...n due to the fact that multilayered boards are generally not affected However you may feel the need to replace the timing chain with the modified circuit if your MTX is suffering from intermittent fir...

Page 51: ...47 MTX Service Manual...

Page 52: ...back panel You will find that your TV Monitor picture will tear or wobble if your plastic back panel does not have a Earth straps b 47pf capacitor Illustration of assembly of power transistor MTX Serv...

Page 53: ...49 PARTS LIST FOR THE MTX 512 04 RS232 I F 32K MEMORY EXPANSION ROM EXPANSION MTX Service Manual...

Page 54: ...05CKC 5v Regulator 1 RG2 REG UA7812 UA7812CKC 12v Regulator 1 RG1 SCRW M38BH M38 Dome Head Screw 3 Q4 RG1 RG2 SCRW M38N M38 Nylon Pan Head Screw 4 J4 J5 TRL TIP2955 TIP2955 Transistor 1 Q4 WSH M3N M3...

Page 55: ...ONL SHUNT02 2 Way Shunt Jumper 1 LK9 CONL WIRE Wire Link 39 24 SWG 11 LK1c 2c 3h 4c 5c 6 2r4c 7 4 10 11 R28 CONP DIN6 6 Way DIN PCB MT 1 J9 CONP HDILR34 34 Way DIL R A Header 1 J6 CONP HSIL02 2 Way SI...

Page 56: ...S00N 1 IC9 ICLS 004 SN74LS04N 2 IC8 IC10 ICLS 008 SN74LS08N 1 IC32 ICLS 027 SN74LS27N 1 IC5 ICLS 074A SN74LS74AN 1 IC31 ICLS 138 SN74LS138N 2 IC17 IC25 ICLS 157 SN74LS157N 2 IC16 IC24 ICLS 193 SN74LS1...

Page 57: ...39 RES K047 47K OHM 1 4W C FILM RES 1 R28a RES K100 100K OHM 1 4W C FILM RES 2 R16 R30 RES K820 820K OHM 1 4W C FILM RES 1 R29 RESW 010W2 5 10R 1 2E C FILM RES 1 R62 SCRW 4407 8 440 7 8 Nylon Screw 1...

Page 58: ...3 C42 C62 CAPE R002235 22uf 35v Radial Cap 1 C34 CAPE R004716 47uf 16v Radial Cap 1 C43 CAPE R010025 100uf 25v Radial Cap 2 C41 C63 CAPP NF0100 100nf Polyester Cap 7 C29 C33 C35 C47 CAPT PF05540 5 5 4...

Page 59: ...1 RV1 RES 560R 560 OHM 1 4W C FILM RES 2 R59 R63 RES K001 1K OHM 1 4W C FILM RES 4 R41 R51 R52 RES K001 5 1K5 OHM 1 4W C FILM RES 1 R44 RES K001 8 1K8 OHM 1 4W C FILM RES 1 R57 RES K001M 1K OHM 1 4W...

Page 60: ...tch Mounting Plate 1 PCB MKBD104 KBD 01 04 PCB 1 SWT ML 3 CM ML 3 CM Keyboard Switch 79 MTX KEYBOARD MEMOTECH ITEM DESCRIPTION NO PCB COMPONENT LOCATION PART NO UNIT COMMENTS KYTP 0011F 0 1 KYTP 0186F...

Page 61: ...BRK 1 KYTP A000F A 1 KYTP A0033F ALPHA LOCK 1 KYTP AA127F ARROW DOWN 1 KYTP B000F B 1 KYTP B033F BS 1 KYTP BB00F 1 KYTP BB01F 1 KYTP BLANKF BLANK KEYTOP 2 KYTP C000F C 1 KYTP C021F CTRL 1 KYTP D000F D...

Page 62: ...F00F 1 KYTP G000F G 1 KYTP GG00F 1 KYTP H000F H 1 KYTP HH000F _ 1 KYTP HH05F 1 KYTP I000F I 1 KYTP J000F J 1 KYTP JJ00F 1 KYTP JJ03F 1 KYTP K000F K 1 KYTP KK00F 1 KYTP KK16F 1 KYTP L000F L 1 KYTP L054...

Page 63: ...K GT8C SPACE BAR KIT 1 MTX POWER SUPPLY UNIT MEMOTECH ITEM DESCRIPTION NO PCB COMPONENT LOCATION PART NO UNIT COMMENTS CBL 2M 2M Mains Cable UK 1 CBL 100MM 10cm Mains Lead 1 CBL DIN6 6 Pin DIN Plug 1M...

Page 64: ...re 1 MLD RPPMTX MTX Rear Plug Moulding 1 MLD RS232CV RS232 Plastic Cover 2 MTX FINAL ASSEMBLY PACKING MEMOTECH ITEM DESCRIPTION NO PCB COMPONENT LOCATION PART NO UNIT COMMENTS EPLH MTX Left Hand End P...

Page 65: ...oax Cable 1 GUAR 512UK 512 UK Guarantee Card 1 MLD MTXCVR Plastic Cartridge Cover 1 PPK MTX512 MTX 512 Polypack 1 STNP 029 MTX Series Manual 1 STNP 078 MTX 512 Serial No Label 1 STNP 236 MTX Series Br...

Page 66: ...0 Way Connector Key5 1 J0 CONS DIL14 14 Way DIL Socket 3 IC12 IC14 CONS DIL20 20 Way DIL Socket 1 IC8 CONS DIL40 40 Way DIL Socket 1 IC1 CONS HDIL60 60 Way DIL Header 1 J1 CONS HDIL02 2 Way DIL Header...

Page 67: ...ITEM DESCRIPTION NO PCB COMPONENT LOCATION PART NO UNIT COMMENTS ASSY CBL5WAY 5 Way Cable Assembly 1 ASSY CBL8WAY 8 Way Cable Assembly 1 BOX RS232 RS 232 Box 1 FACC BAG21 4 Mini Grip Poly Bag 2 1 4sq...

Page 68: ...CLS 004 SN74LS04N 1 IC3 ICLS 157 SN74LS157N 2 IC5 IC6 ICLS 244 SN74LS244N 1 IC4 ICPR 6301 6301 1N PROM 1 IC1 ICRA 323732 32K Partial D Rams 8 IC7 IC14 ICS 74S37 SN74S37N 1 IC2 PCB MEMEXT MTX Memory Ex...

Page 69: ...o Lo CONL WIRE Wire Link 39 24 SWG 5 41 51 61 71 16 CONS DIL20 20 Way DIL Socket 1 IC5 CONS DIL28 28 Way DIL Socket 4 IC1 IC4 CONS EDGE60 30 30 Way Connector 1 J0 DODE IN4148 IN4148 Silicon Diode 8 D1...

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Page 75: ...nd 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 Node commands are provided to set the b...

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Page 77: ...This manual was brought to you by ROBCFG MTX Service Manual...

Page 78: ...MTX Service Manual...

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