Acorn Electron Service Manual

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To test the cassette input, press BREAK and measure the quiescent voltage of each of the three amplifier outputs, pin 7, pin 8 and pin 14 of IC 13. This voltage should not be greater than 100mV. If any of these pins is at too high a voltage then replace the LM324. To test the input, L 0 A D a program from a cassette which is known to work and check that a signal is arriving at pin 59 of the ULA with an amplitude of between 500mV and 2V. 8.9 Keyboard The PIT system will test the keyboard. A manual check is possible using an ohm meter and the keyboard circuit diagram. Check for shorts, dry joints and lifted tracks. Replace any faulty keys. Check that both ends of the keyboard connector cable are making good contact, that the connector on the <strong>Electron</strong> end of the cable is covering all the pins (it could be inserted with an offset and miss some of the pins), and that the cable is not damaged in any way. Check that the diodes and resistors are correctly fitted and are of the correct value. 8.10 Sound If the <strong>Electron</strong> will accept commands then give a SOUND command and check that there is a signal from pin 62 of the ULA (IC1): If not then replace the ULA with a known good one and try again. Check all the connections in the simple amplifier circuit to the loudspeaker, especially transistors Q3 and Q4 (see circuit diagram). 14
Appendix Diagnostic flowcharts 8.1 Power supply 15
Page 3 and 4: Electron Service Manual Part no 040
Page 5: Contents 1 Introduction 1 2 Packagi
Page 8 and 9: 2 Packaging and installation The El
Page 10 and 11: - Keyboard and keyboard buffer. - S
Page 12 and 13: 4 Disassembly and assembly To servi
Page 14 and 15: 6 The uncommitted logic array (ULA)
Page 16 and 17: 8 Fault finding inside a dead Elect
Page 18 and 19: ) If the RGB works but the UHF does
Page 22: 8.2 Oscillator 16
Page 25 and 26: 8.5 ROM 19
Page 27 and 28: 8.7 Video 21
Page 29: 8.10 Sound 23
Page 33: Electron block diagram
Page 37: Main PCB circuit diagram
Page 41: Main PCB silk-screen
Page 45: Keyboard matrix
Page 48 and 49: 18 19 890,001 Rubber foot 4 20 - 21
Page 50 and 51: 98 820,160 Crystal 16MHz 1 X1 99 10
Page 52: NOTES

Acorn Electron Service Manual

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