Troubleshooting the Plus/4 Using an Oscilloscope - Plus/4 Encyclopedia



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Troubleshooting the Plus/4 Using an Oscilloscope
Category Hardware/Troubleshooting Topic Here you can find oscillograms for the Commodore Plus/4 (NTSC). I recorded them following the instructions from the original service manual. 1) NO VIDEO - absolutely no video on screen b) Check for oscillation at pin 14 of U1 (TED) c) Check for LUM signal at pin 23 of U1 at FB3 e) Check for control signals: AEC - pin 35 of U1 CAS - pin 11 of U1 CS1 - pin 6 of U1 CS0 - pin 5 of U1 R/W - pin 7 of U1 MUX - pin 9 of U1 IRQ - pin 8 of U1 BA - pin 34 of U1 RAS - pin 10 of U1 2) - BAD VIDEO - Scrolling lines on screen - Random blocks on screen - Blurred display E) Check RAM data lines for correct amplitude Pin 5 of U11 - U18 Pin 6 of U11 - U18 Pin 7 of U11 - U18 Pin 9 of U11 - U18 Pin 10 of U11 - U18 Pin 11 of U11 - U1 Pin 12 of U11 - U1 Pin 13 of U11 - U1 F) Check multiplexers U9, U10 - signals at RP3 and RP4 should be similar in frequency and amplitude Keywords oscilloscope plus/4 troubleshooting service manual signal level check