Sinclair ZX SPECTRUM+ - Page 3

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