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Sinclair Research ZX SPECTRUM Servicing Manual

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SECTION 1
SECTION 2
SECTION 3
SECTION 4
SECTION 5
i
ZX Spectrum Block Diagram
Expansion RAM RAS/CAS Timing (Read Cycle shown)
Keyboard Matrix
ZX Spectrum (Issue 2) Circuit Diagram
ZX Spectrum (Issue 3) Circuit Diagram
Keyboard Format
Speaker Load Input Waveforms
Expansion Memory 1C Locations
Issue 3 Links vs 1C Manufacturer and Type
Printed Circuit Board
Printed Circuit Board
Printed Circuit Board
Prepared by THORN (EMI) DATATECH LTD
for SINCLAIR RESEARCH LTD
© Sinclair Research Ltd.
SERVICING MANUAL
FOR
ZX SPECTRUM®
LIST OF CONTENTS
DISASSEMBLY/ASSEMBLY
SETTING UP AND SYSTEM TEST
LIST OF ILLUSTRATIONS
Interconnections
(Issue 2)
Component Layout
(Issue 3)
Component Layout
(Issue 3B) Component Layout
( i )
INTRODUCTION
SYSTEM DESCRIPTION
FAULT DIAGNOSIS AND REPAIR
PARTS LISTS
i
Fig No.
1.1
1.2
1.3
1.4
1.5
4.1
4.2
4.3
4.4
5.1
5.2
5.3
MARCH 1984

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  • Page 1 Fig No. ZX Spectrum Block Diagram Expansion RAM RAS/CAS Timing (Read Cycle shown) Keyboard Matrix Interconnections ZX Spectrum (Issue 2) Circuit Diagram ZX Spectrum (Issue 3) Circuit Diagram Keyboard Format Speaker Load Input Waveforms Expansion Memory 1C Locations Issue 3 Links vs 1C Manufacturer and Type...
  • Page 2 SINCLAIR dealers, engineers and representatives as a guide to rectifying f a u l t s on the SINCLAIR ZX SPECTRUM personal computer. The m a n u a l refers p r i n c i p a l l y to the Issue 2 and...
  • Page 3 - SAFETY MEASURES• This instruction manual contains certain — WARNING — CAUTION notices which MUST be- followed by the user to ensure SAFE operation retain equipment in a SAFE condition. Any adjustment, maintenance and repair of the opened apparatus under voltage shall carried cut only by a skilled person who is...
  • Page 4 Fig. 1.4 ZX Spectrum, Issue 3 Fig. 1.5 INTRODUCTION A block diagram of the complete ZX SPECTRUM micro-computer is given in Figure 1.1. It is valid for all build standards, fitted with either 16k or 48k bytes of dynamic RAM memory.
  • Page 5 Z80A CPU The Z80A is an 8-bit s i n g l e - I C central processing unit (CPU). It is clocked at 14.0 MHz from an external source controlled by the logic gate array (ULA) standard three input/output arrangement.
  • Page 7 Dynamic Memory Refresh. The CPU incorporates b u i l t - i n dynamic RAM refresh circuitry. As part of the instruction OP code fetch cycle, the CPU performs a memory request after first p l a c i n g the refresh address on the lower eight bits of the address bus.
  • Page 14 m e c h a n i s m a l l o w i n g the CPU to read the extension ROM in the interface for m i c r o d r i v e and RS232 a p p l i c a t i o n s . 4.5.3 L i n k s H and N, shown directly above IC5, a l l o w a second source ROM to be fitted.
  • Page 15 4.5.9 32k Expansion RAM (IC15-IC32). The eight 32k ICs m a k i n g up the 32k x 8 bit expansion RAM are in fact 64k ICs with either row or column drop-out rendering one half of the memory n o n - f u n c t i o n a l . In order to accommodate the Texas Instruments RAM (Type TMS 4532) or the optional OKI RAM (Type MSM3732) a set of l i n k s are provided, v i s i b l e on the...
  • Page 16 FIG 1.2 EXPANSION RAM RAS/CAS TIMING (READ CYCLE SHOWN)
  • Page 17 5.2.2 U s i n g the 14 MHz clock the ULA derives l i n e and f i e l d t i m i n g compatible with the external TV receiver. Video is derived by accessing the memory mapped display area in the RAM in a set seguence times throughout picture...
  • Page 19 5.3.2 When the keyboard s c a n n i n g routines are entered the CPU performs successive I/O read cycles setting the IOREQ and RD lines to the IJLA, low. At the same time, the I/O port addresses placed on the upper h a l f of the address bus are m o d i f i e d with each cycle such that each of the address l i n e s A15 through A8 is set l o w in t u r n , the other l i n e s r e m a i n i n g h i g h .
  • Page 20 POWER SUPPLIES The on-board power s u p p l y unit receives a 9V u n r e g u l a t e d supply from the external S i n c l a i r ZX power pack and derives the f o l l o w i n g internal supply r a i l s : (a) regulated +5V for the 1C logic c i r c u i t s , the ULA and the U H F m o d u l a t o r ,...
  • Page 21 SECTION 2 DISASSEMBLY/ASSEMBLY Sub-Section LIST OF CONTENTS Page No. Disassembly Assembly DISASSEMBLY U n p l u g all input/output leads and turn the computer upside-down to reveal five self-tapping screws. Remove the screws. Hold the two halves of the case together and return the computer to the keys uppermost position.
  • Page 22 When a l i g n i n g the top h a l f of the case with the bottom h a l f ensure that the two keyboard ribbon cables are not trapped between projecting components w i t h i n the case. In their correct positions there is s u f f i c i e n t room for the cables to take up a comfortably curved...
  • Page 23 To carry out the setting up procedure it is first necessary to remove the ZX SPECTRUM from the case (Section 2, A s s e m b l y / D i s a s s e m b l y ) .
  • Page 24 Pot. IC14 Factory Settinq Optimum ( m V ) Overall Ranqe Pin No. (mV) Voltage Tolerance (mV) 130 ± 20 +45 to +150 75 ± 20 -45 to -100 Sub-Carrier Oscillator. The chrominance sub-carrier o s c i l l a t o r frequency should be 4.433619 MHz ±...
  • Page 25 SYSTEM TEST The system test for the Spectrum may be undertaken using the ZXTP taped program (see Test Equipment Section loaded conventionally; this requires that the keyboard is connected. test should be carried out with the Spectrum connected to its own power supply.

  • Page 26: Table Of Contents

    SECTION 4 FAULT DIAGNOSIS AND REPAIR Sub-Section LIST OF CONTENTS Page No. Introduction Test Equipment Modification History Modifications - Issue 1 Board Modifications - Issue 2 Board 32k Extension Memory - (16k-48k) Hitachi vs NEC ROM Fault Diagnosis Techniques Power Supply Unit I n i t i a l i s a t i o n Memory Check Keyboard Structure...

  • Page 27: Introduction

    The ZX SPECTRUM is s u p p l i e d with either 16k or 48k of on-board RAM. 16k version is wired so that it can be expanded to 48k by the addition of a number of appropriate p l u g - i n ICs.

  • Page 28: Modification History

    Modification History Two major m o d i f i c a t i o n s have been implemented on the Spectrum boards: A m o d i f i e d layout of board (i.e. Issue 1, Issue 2 and Issue 3) Issue 1.

  • Page 29: 1.3 Modifications - Issue 1 Board

    Board Issue No ULA Type 5C112 6C001 6C001 Component R 4 7 2 2 0 a 8 k2 10 k 10 k R 5 6 2 2 0 n 4 7 0 220 n 470 n 1.3 Modifications - Issue 1 Board A number of m o d i f i c a t i o n s were introduced, and these should be checked for and,...

  • Page 30: Modifications - Issue 2 Board

    Modifications - Issue 2 Board A number of m o d i f i c a t i o n s have also been introduced for the Issue 2 board. These should checked a n d , necessary, introduced retrospectively. These components should be changed if colour quality needs u p g r a d i n g :...

  • Page 31: Hitachi Vs Nec Rom

    W i t h a densely populated board such as the ZX SPECTRUM, a careful physical examination of the board can sometimes indicate an obvious fault.

  • Page 32: Power Supply Unit

    ' i n i t i a l i s e ' produce a clear screen with the statement (01982 Sinclair Research Ltd d i s p l a y e d in the lower left section of the screen.

  • Page 33: Memory Check

    If these tests prove satisfactory check IC1 pin 14, IC2 pin 11 and IC5 pin 28 for +5V. Also check for ground at IC1 pin 40, IC2 pin 29 and IC5 p i n 14. If all is s t i l l satisfactory at this point and IC1 is the p l u g - i n type, replace IC1.
  • Page 34 for a 48k unit - 65535 for a 16k u n i t - 32767 The v a l u e printed in each instance is the last v a l i d memory l o c a t i o n , and in a serviceable u n i t would be as set out above.

  • Page 35: Keyboard Structure

    Keyboard Structure The keyboard is connected horizontally in eight blocks of five keys and vertically m five blocks of eight keys. configuration. It follows that if any block of five keys fail the Figure 4.1 shows the fault is with KB2 circuitry or the 8-way membrane, and that if any block of eight keys fail the fault is with KB1 circuitry or the 5-way membrane.

  • Page 36: Fault-Finding Guide

    Fault-Finding Guide As with any complex d i g i t a l equipment the possible fault permutations are vast, thus the following table is not intended to be an exhaustive list of the f a u l t s that might occur on the Spectrum. It is intended as a guide only to possible courses of action to f o l l o w when f a u l t s show up in p a r t i c u l a r areas of the c i r c u i t .
  • Page 37 AREA SYMPTOM ACTION No video, (contd) No VIDEO INPUT at Check waveform IC14 IC14 pin 12. pin 13. If correct check TR1 and TR2. Check waveforms pins 15, 16 and 17: If correct check VR1, (Issue 1 and Issue 2 boards). Change IC1.
  • Page 38 AREA SYMPTOM ACTION Video Incorrect. Dark Screen. Check t u n i n g . Change modulator. Dim ' S i n c l a i r ' Io9°- 1' Check +12V" Check high impedance. Check R52. 4. Check +5V on IC14 pin 3. Wavy lines across Press down...
  • Page 39 AREA SYMPTOM ACTION Colour tuning VRl or VR2 d.c. Change IC14. f a u l t s , ( c o n t ' d ) shifts IC14 pin 13 waveform. Alternate dark lines Change IC14. on screen. No colour after trimming TC2: ICH pin 17 not Check crystal X2.
  • Page 40 AREA SYMPTOM ACTION Colour faults Intermittent Change TC2 (Issue 1 and ( c o n t ' d ) colour. Issue 2 boards). Change IC14. Red, Blue or Change IC1. Green 'Sinclair' logo. Washed-out Check TR2. colours. Keyboard faults. KB1 fault. Check for short on 2 or more of the 5 tracks.
  • Page 41 AREA SYMPTOM ACTION Test Program. Paper area corrupts Change IC1. (cont'd) d u r i n g tests. Carry f a u l t - f i n d i n g procedure (paragraph 2 . 2 ) . Border colours are Change IC14.
  • Page 42 FIGURE 4.2 SPEAKER LOAD INPUT WAVEFORMS 4.17...
  • Page 43 TABLE 4.1. IC14 (IML889) PIN SIGNALS Pin No. Signal (CHROMA LEAD) SINEWAVE BOOmV, 0.2yS, d.c. 9.5V (R - Y INPUT) (CHROMA BIAS) d.c. 4.8V (B - Y INPUT) 0V (GROUND) (VIDEO INPUT) d.c. 12V unreg. (CHROMA SUBCARRIER) (R.F SUPPLY) (SOUND TANK) ' L I N K E D 1 12V d >...

  • Page 44: Repair

    REPAIR Renewal components should carried u s i n g recognised d e s o l d e r i n g / h e a t s i n k i n g techniques to prevent damage to the component or to the printed circuit board.

  • Page 45: Issue 2 Board

    Issue 2 Board The ICs used on this board are as follows: TYPE IC15 - IC22 TI 4532-3 or TI 4532-4 200ns (or 250ns) IC23 74LS32 IC24 74LSOO IC25, IC26 74LS157 (NOT N a t i o n a l Semiconductors) NOTES: (1) All external RAM ICs must be of the same type (i.e.
  • Page 47 FIGURE 4.4 ISSUE 3 LINKS vs 1C MANUFACTURER AND TYPE 4.22...
  • Page 49 LIST OF CONTENTS Page No. Introduction Notes to Table 5.2 INTRODUCTION Parts lists for the ZX SPECTRUM are provided in table form; one for the case assembly (Table 5.1) and another for the board assembly (Table 5.2). The latter covers the Issue 2 and 3 Spectrums and is related to the board layout diagrams given in Figure 5.1 and 5.2.
  • Page 50 General Capacitor Change. Early Issue 2 units were manufactured u s i n g a considerable number of 47 nF and 100 nF disc capacitors. Where these occur the service engineer should take the opportunity to replace C41 and C49 with axial types. TABLE 5.1 CASE ASSEMBLY MANUFACTURER D E S C R I P T I O N...
  • Page 52 TABLE BOARD ASSEMBLY Circuit Issue 2 Issue 2 Notes Issue 3 R a t i n g / Manufacture Reference Type CAPACITORS ( U n l e s s otherwise stated a l l c a p a c i t o r s are a x i a l types) C1-C8 47 nF 47 nF...
  • Page 53 CONNECTORS Reference Description M a n u f a c t u r e r / Part Number 3.5 mm jack socket M I C 3.5 mm jack socket P W R 2.1 mm co-axial socket 5-way ribbon connector M o l e x 5229-05CPB 8-way ribbon connector Molex 5229-08CPB CRYSTALS...
  • Page 54 RESISTORS ( 1 / 4 W , 5% unless otherwise stated) Circuit Issue 2 Issue 2 Notes Issue 3 Rating Issue 3B Reference R1-R8 470R 470R R9-R16 R17-R23 330R 330R 180R 180R R26/R27 680R 10KO 220KO 220K 100R 100R 680R 680R 1/2 or 1W 10KO...
  • Page 55 TRANSISTORS C i r c u i t Issue 2 Issue 2 Notes Issue 3 Reference TR1/TR2 ZTX313 ZTX313 ZTX313 ZTX313 ZTX650/TIPP31 ZTX650 ZTX213 ZTX213 ZTX313 ZTX313 ZTX450 TR8/TR9 BC184 MISCELLANEOUS Reference D e s c r i p t i o n M a n u f a c t u r e r / Part Number 5V r e g u l a t o r...
  • Page 56 GENERAL DATA Earliest version very pale brown keys. Second version grey keys Third/Fourth versions - grey keys, but heatsink now visible through the edge connector slot Early Spectrum plus same as fourth type. Dissembly after removing the screws, t i l t back, face up and carefully lift the top taking care not to break any of the keyboard tails.
  • Page 57 Other Service/Repair Manuals by T.I.S. Include:- Rank A823 CTV Chassis Philips G8 CTV Chassis Thorn 3000/3500 CTV Chassis Thorn 8000/8004/8500/8600 CTV Chassis Rank T20/20A CTV Chassis The Tunbridge & McCourt T.V. Repair Manuals The Tunbridge Video Repair Manuals...
  • Page 58 SERVICE DATA Modification of earplug: Connect a 330 ohm resistor between signal and earth leads of earplug to a l l o w earplug to be left in place while saving a programme. Inserting or removing such items joysticks, especially via a Kempston interface, while computer is switched on will damage the power resistors...
  • Page 59 REPAIR DATA 1) GENERAL REPAIR PROCEDURE AND NOTES ON ALL FAULTS These computers are reportedly very unreliable with some 50% of new ones alleged to have to be returned for replacement. Many faults are due to loose or badly fitted components so that a good checkover is essential for this reason, to determine if a factory failure first.
  • Page 62 Early circuit showing presets Td, TC2, VRl and VR2 to match the early type boards. Note:- the different pins 16/17 setup from Id in the generalised circuit diagram shown in the middle pages. In very versions instead of TR6 a somewhat unreliable, resistor/diode was used which should be modified as shown in the centre pages.
  • Page 63 3) NO COIL BUZZ FROM INVERTER, -5V ABSENT From symptom 1 it should be obvious that TR4 (ZTX650) is very prone to damage and this symptom is a sure indication that TR4 must be replaced. How- ever, before replacing the TR4 check the TR5 (ZTX213) (using a transistor tester is O.K.) and the coil since it is not unknown for all three to have gone at the same time and if only the TR4 is replaced it can fail again immediately...
  • Page 64 6) CONTINUAL FAILURE OF POWER SUPPLY TRANSISTORS Ensure that all modifications have been carried out and that the edge connector is O.K. and not loose or, damaged. Check for proper fitting of all peripherals and verify that owner is not persistently inserting/removing any of the add-ons, etc.
  • Page 65 10) TEXAS SN1889 INSTEAD OF LHA889 A few models appeared with the SN version and these may even have been used as replacements during repairs. Although unlikely to find now, if SN types have been used replace completely by LH type. 11) POWER SUPPLY O.K.

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