Sinclair ZX Spectrum Service Manual

Sinclair ZX Spectrum Service Manual
Spectrum For Everyone https://spectrumforeveryone.com/
3
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 Specifications

General

Processor	Zilog Z80A
Clock Speed	3.5 MHz
RAM	16KB or 48KB
ROM	16KB
Graphics	256 x 192 resolution
Sound	1-channel beeper
Storage	Cassette tape
Input	Keyboard
Power	9V DC
Release Year	1982
Display	TV via RF modulator
Ports	Expansion, RF
Colors	15 (8 colours with two levels of brightness each, plus black)