The Lil Old ZX Spectrum 48k Service Manual

1. Check TR5 and C44
2. Visually check track
3. Check TR4

1. Change TR4 and TR5 (even though TR5 checks out)
2. Check the TR5 circuit components are to latest specification

1. Change IC1
2. Check TR1 and TR2

1. Visually check IC1 and socket
2. Check for shorting between C65 and R53
3. Carry out Power Supply Unit check

1. Check voltage drop across R64
2. Check +5V regulator O/P and +9V regulator I/P
3. Check PWR socket not shorted
4. Check power unit

1. Check waveform at IC14 pin 13. If correct check TR1 and TR2
2. Check waveforms at IC1 pins 15, 16 and 17

If correct check VR1, VR2 (Issue 1 and Issue 2 boards)

3. Change IC1

4. If +5V and VIDEO INPUT correct change modulator

1. Check IC1 socket
2. Check PWR socket is not intermittent
3. Check IC1 pin 14 for +5V with no discernable ripple

1. Low amplitude - check R25
2. Check TR3
3. Check IC1 pin 32 for 3MHz
4. Check IC1 pin 39 for 14MHz
5. Check crystal X1
6. Check IC1 pin 13 for +3V

1. Check tuning
2. Change modulator

1. Check +12V
2. Check C65 for high impedance
3. Check R52
4. Check +5V on IC14 pin 3

1. Press down on each electrolytic capacitor to see if lines disappear. If so change that capacitor
2. Check crystal X2
3. Check/change TR1 and/or TR2
4. Check/change IC14

1. Check for +3V at IC1 pin 13
2. Change C30

1. Monitor IC14 pin 2 trimming VR2
2. Monitor IC14 pin 4 trimmin VR1
3. Change IC14

1. Check crystal X2
2. Change IC14
3. Change X2

1. Check for broken track
2. Change TR2
3. Change IC14

2. If IC14 pins 2 and 4 are correct, change modulator

1. Change TC2 (Issue 1 and Issue 2 boards)
2. Change IC14

1. Check for short on 2 or more of the 5 tracks
2. Change membrane

1. Check for short on 2 or more of the 8 tracks
2. Change membrane

1. Check load input waveforms
2. Check TR7
3. Check D9
4. Change speaker