8 - Test equipment 35 9 - Fault finding 36 9.1 Switch on 36 9.2 Power supply 39 9.3 Oscillator and divider circuitry 40 9.4 CPU 40 9.5 ROM 41 9.6 DRAMs 42 9.7 Video 42 9.8 Cassette interface and RS423 45 9.9 Keyboard 47 9.10 Disc interface 48 9.11 Printer port 51 9.12 User port 52 9.13 1MHz extension bus 53 9.14 TUBE interface 54 9.15 Analogue to digital conversion 55 9.16 ECONET 56 Appendix 57 Connector pinouts 58 Parts list 63 Glossary 69 IC description 71 Final assembly 89 Circuit block diagram 91 PCB circuit diagram 93 PCB layout 95 Keyboard circuit diagram 97 Power supply circuit diagram 99