ZX Spectrum Service Manual Spectrum for Everyone

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Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com. 1 Introduction 7,1 1 Introduction 7,1 2 Architecture 8. 1 3 Z80A CPU 8,1 3 1 Data Bus 8,1 3 2 Address Bus 8. 1 3 3 Control Bus 8,1 3 4 CPU Clock 9,1 3 5 Dynamic Memory Refresh 9. 1 4 Memory Organisation 9,1 5 Read Write Operations 10.
1 5 1 Read Only Memory IC5 10,1 5 2 Standard 16k RAM IC6 IC13 10. 1 5 3 32k Expansion RAM IC15 IC32 11,1 6 Input Output 13. 1 7 TV Picture Generation 13,1 8 Keyboard Scanning 14. 1 9 Tape Interface 15,1 10 Loudspeaker BEEP Operation 15. 1 11 Power Supplies 15,2 Disassembly assembly 16,2 1 Disassembly 16.
2 2 Assembly 16,3 Setting Up and System Test 17,3 1 General Alignment 17. 3 1 1 Introduction 17,3 1 2 Voltage Check 17,3 1 3 Colour Adjustment 18. 3 1 4 Sub Carrier Oscillator 18,3 1 5 14 MHz Oscillator 18. 3 2 System Test 19,Sinclair ZX Spectrum Service Manual. Spectrum For Everyone https spectrumforeveryone com. 4 Fault Diagnosis and Repair Getting Started 20,4 1 Introduction 20.
4 1 1 Test Equipment 20,4 1 2 Modification History 21. 4 2 Modifications Issue 1 Board 22,4 3 Modifications Issue 2 Board 23. 4 4 Modifications Issue 3B Board 23,4 5 32k Extension Memory 16k to 48k 23. 4 5 1 Board Issue 1 23,4 5 2 Board Issue 2 23,4 5 3 Board Issue 3 24. 4 6 Hitachi vs NEC ROM 24,5 Fault Diagnosis and Repair PSU and Memory 25.
5 1 Fault Diagnosis Techniques 25,5 2 Power Supply Unit 25. 5 3 Initialization 26,5 3 1 Basic Checks 26,5 4 Memory Check 27. 5 4 1 Example 28,5 5 Keyboard Structure 29,6 Fault Diagnosis and Repair Input Output 30. 6 1 TV screen dead smoke appears on switch on Not Initialising 30. 6 1 1 TR4 base collector shorted 30,6 1 2 Short persists with TR4 removed 30. 6 1 3 TR4 blows again 30,6 2 No video 31,6 2 1 No video 31.
6 2 2 No video after ULA changed 31,6 2 3 No 5V input 31. 6 2 4 No VIDEO INPUT at IC14 pin 12 31,6 3 Corrupt Paper after ULA change 32. 6 3 1 Initial Check 32,6 3 2 No 3MHz at IC2 pin 6 32. Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com. 6 4 Video Incorrect 32,6 4 1 Dark Screen 32,6 4 2 Dim Sinclair logo 32.
6 4 3 Wavy lines across screen 32,6 4 4 Self resetting 32. 6 4 5 Random dynamic squares 32,Paper area too low 32. 6 4 6 Diagonal lines in the border area 32,6 4 7 Distorted video 33. 6 5 Colour tuning faults Issue 1 and Issue 2 boards 33. 6 5 1 Initial check 33, 6 5 2 VR1 or VR2 fails to adjust IC14 pin 13 waveform 33. 6 5 3 VR1 or VR2 DC shifts IC14 pin 13 waveform 33. 6 5 4 Alternate dark lines on screen 33,6 5 5 No colour after trimming TC2 33.
6 6 Colour Faults Issue 1 Issue 3 boards 34,6 6 1 Pin screen 34. 6 6 2 Blue haze around Sinclair logo 34,6 6 3 Screen too yellow 34. 6 6 4 Intermittent colour 34,6 6 5 Red Blue or Green Sinclair logo 34. 6 6 6 Washed out colours 34,6 7 Keyboard Faults 34. 6 7 1 KB1 fault 34,6 7 2 KB2 fault 34,6 7 3 Dead keyboard 34.
6 7 4 Wrong keyboard response 34,6 7 5 Keyboard response too fast 34. 6 8 Regulator Coil 34,6 8 1 Coil excessively noisy 34. 6 9 Speaker 35,6 9 1 No speaker output 35,6 10 Speaker Load Input Waveforms 35. Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com. 7 Fault Diagnosis and Repair Colour Repair and Upgrades 36. 7 1 IC14 LM1889 Pin Signals 36,7 2 Repair 37,7 3 16k to 48k Upgrade 37.
7 3 1 Integrated Circuits Link Settings 37,7 3 2 Issue 2 Board 37. 7 3 3 Issue 3 Board 38, 7 3 4 Issue 3 Links vs IC Manufacturer and Type 39. 7 3 5 Expansion Memory IC Locations 40,8 Parts List 41. 8 1 Introduction 41,8 2 Notes to Parts List 41,8 3 General Capacitor Change 42. 8 4 Case Assembly 42, 8 5 Capacitors All axial types unless otherwise stated 43.
8 6 Coil 44,8 7 Connectors 44,8 8 Crystals 44,8 9 Diodes 44. 8 10 Integrated Circuits 44, 8 11 Resistors All 1 4W 5 unless otherwise stated 45. 8 12 Transistors 46,8 13 Miscellaneous 46,9 Supplement No 1 47. 9 1 Introduction 48,9 2 DC DC Converter Modification 48. 9 2 1 Circuit Operation 50, 9 3 Issue 3B Board Already covered in existing manual 50.
9 4 Issue 4 Board None issued 50,9 5 Issue 4A Board 50. 9 6 Issue 4B Board 50,9 7 Issue 5 Board 50,9 8 Issue 6 Board None issued 51. Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com. 9 9 Issue 6A Board 51,9 10 Fault Finding Servicing Addenda 51. 9 11 Warranty Seal 51,9 12 Parts Lists 51,9 12 1 Notes 51.
9 13 Capacitors Unless otherwise stated all are axial types 52. 9 14 Coil 53,9 15 Connectors 53,9 16 Crystals 53, 9 17 Resistors 0 25W 5 tolerance unless otherwise stated 54. 9 18 Diodes 55,9 19 Integrated Circuits 55,9 20 Transistors 56. 9 21 Miscellaneous 56,10 Supplement No 2 57,10 1 Introduction 57. 10 2 Conversion Procedure Spectrum to Spectrum 57,10 3 Assembly of the Keyboard for the Spectrum 58. 10 4 Keyboard Operation 58,10 5 Spectrum Keyboard Top Membrane 59.
10 6 Spectrum Keyboard Lower Membrane 60,Sinclair ZX Spectrum Service Manual. Spectrum For Everyone https spectrumforeveryone com. 1 INTRODUCTION,Introduction,Architecture,Memory Organisation. Read Write Operations,Input Output,TV Picture Generation. Keyboard Scanning,Tape Interface,Power Supplies,1 1 INTRODUCTION. A block diagram of the complete ZX Spectrum micro computer is given below It is valid for all build. standards fitted with either 16k or 48k bytes of dynamic RAM memory Although functionally identical. detailed circuit changes have been introduced to improve reliability and to assist with manufacture The. printed circuit board layout has also been modified Details of these changes are highlighted where. necessary in the following paragraphs and in later sections referring to fault diagnosis and repair. Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com.
1 2 ARCHITECTURE, The architecture of the Spectrum shown above is typical of many microcomputer systems in that it. comprises a single microprocessor board in this instance a Z80A or u780 CPU a read only memory ROM. an expandable RAM memory and an input output section handling the keyboard tape and TV display. functions The latter is recognisable as the logic gate array ULA and the three functional blocks shown in. the right of the diagram, The computer is built on a single printed circuit board which also includes a regulated power supply fed. from an external 9V power pack The keyboard matrix is part of the upper case assembly and is connected. to the board via two ribbon cables KB1 and KB2 A description of each section follows. 1 3 Z80A CPU, The Z80A is an 8 bit single IC central processing unit CPU It is clocked at 14 0 MHz from an external. source controlled by the logic gate array ULA and has a standard three bus input output arrangement. These buses are the Data Bus Address Bus and Control Bus respectively. 1 3 1 Data Bus, D7 D10 constitutes an 8 bit bi directional data bus with active high tri state input outputs It is used for. data exchanges with the memory and with the ULA,1 3 2 Address Bus.
A15 A0 constitutes a 16 bit address bus with active high tri state outputs The address bus provides the. address for memory up to 64k bytes data exchanges and for data exchanges with the ULA It is also used. during the interrupt routine when scanning the keyboard matrix. 1 3 3 Control Bus, The control bus is a collection of individual signals which generally organise the flow of data on the address. and data buses The block diagram only shows five of these signals although others of minor importance. are made available at the expansion port, Starting with memory request MREQ this signal is active low indicating when the address bus holds a. valid address for a memory read or memory write operation Input Output request IORQ is also active. low but indicates when the lower half of the address bus holds a valid I O address for the ULA during I O. read write operations, The read and write signals RD and WR are active low and one or other is active indicating that the CPU. wants to read or write data to a memory location or I O device All the control signals discussed so far are. active low tri state outputs, The last control signal described here is the maskable interrupt INT This input is active low and is. generated by the ULA once every 20ms Each time it is received the CPU calls the maskable interrupt. routine during which the real time is incremented and the keyboard is scanned. Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com.
1 3 4 CPU Clock, Returning to the CPU clock mentioned earlier in this section the ULA is able to inhibit this input bringing. the CPU to a temporary halt This mechanism gives the ULA absolute priority allowing it to access the. standard 16k RAM without interference from the CPU see RAM description Switching transistor TR3. ensures that the clock amplitude is 5V rather than some arbitrary TTL level This is essential if the CPU is. to operate effectively while executing fast machine code programs of the space invader type. 1 3 5 Dynamic Memory Refresh, The CPU incorporates built in dynamic RAM refresh circuitry As part of the instruction OP code fetch cycle. the CPU performs a memory request after first placing the refresh address on the lower eight bits of the. address bus At the end of the cycle the address is incremented so that over 255 fetch cycles each row of. the dynamic RAM is refreshed This mechanism only applies to the optional 32k expansion RAM in the 48k. Spectrum An alternative refresh method is adapted for the standard 16k RAM. 1 4 MEMORY ORGANISATION, In the standard 16k Spectrum there are 32k bytes of addressable memory equally divided between ROM. The lower 16k bytes of memory addresses 0000 3FFF are implemented in a single ROM IC5 which. holds the monitor program This program is a complex Z80 machine code program divided broadly into. three parts one each covering the input output routines the BASIC interpreter and expression handling. Details of the program content although outside the scope of this manual are referred to as necessary. The upper 16 bytes of memory addresses 4000 7FFF are implemented using eight 16k bit dynamic. RAMs IC6 IC13 Approximately half of this space is available to the user for writing BASIC or machine. code programs the remainder is used to hold the system variables including 6k bytes reserved for the. memory mapped display area, In the 48k Spectrum an additional 32k bytes of RAM are provided addresses 8000 FFFF which are. implemented using eight 32k bit dynamic RAMs IC15 IC32 The RAM providing extra memory space for. the user is normally fitted during manufacture but may be added retrospectively using the RAM expander. kit In addition to the RAMs the kit includes the address multiplexer and read write control ICs IC23 IC26. Board space and the necessary discrete components are already provided on the board. Sinclair ZX Spectrum Service Manual, Spectrum For Everyone https spectrumforeveryone com.
1 5 READ WRITE OPERATIONS, The following description should be read in conjunction with the circuit diagrams. 1 5 1 Read Only Memory IC5, The CPU addresses the ROM directly during memory read cycles using the address bus A13 A0 MREQ and. RD enable the ROM and the ROM outputs respectively A third input CS derived by the ULA ROMCS. selects the ROM provided the higher order address bits A14 and A15 are both low These are reserved. for accessing the RAM memory which starts with address 4000 i e address A14 set An external ROM IC. select input supplied via the expansion port on pin 25A selectively disables the on board ROM by pulling. the select input high By virtue of R33 placed on the ULA side of the ROM the ULA ROMCS output is. effectively inhibited Interface 1 uses this mechanism allowing the CPU to read the extension ROM in the. interface for Microdrive and RS232 applications, Links H and N shown directly above IC5 allow a second source ROM to be fitted The Hitachi H and NEC. N ROMs use different pins for the enable and select inputs i e pins 20 and 27 The links allow the inputs. to be reversed accordingly,1 5 2 Standard 16k RAM IC6 IC13. The eight 16k RAM ICs making up the standard 16k x 8 bit RAM memory are organised as a matrix of 128. rows x 128 columns Thus separate 7 bit row and column addresses are required to access any one of the. locations These addresses are supplied by the CPU on address bus A13 A0 via an address multiplexer. IC3 IC4 The low order address bits A6 A0 give the row address and are selected at the beginning of the. memory access cycle when initially the RAS output from the ULA is high Later as the row address is. latched RAS goes low selecting the high order address bits A13 A7 giving the column address. The RAS CAS outputs from the ULA are generated in sequence in response to MREQ and A14 from the. CPU The DRAMWE output also from the ULA is a decode of the RD WR waveforms telling the RAM to. expect either a read or write cycle, It is also apparent from the circuit diagram that the ULA can access RAM by generating a set of addresses.
independent of those generated by the CPU The address port for the RAM is therefore dualled by the. Sinclair ZX Spectrum Service Manual Spectrum For Everyone https spectrumforeveryone com 5 7 Fault Diagnosis and Repair Colour Repair and Upgrades 36

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