36 E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Troubleshooting Assembly–Level Problems
Symptom: RPG not working properly
1. Ensure that the front panel green power on LED is on. If it is not on, refer to
“Power Supply Troubleshooting” on page 37.
2. Check the front panel operation by checking random hardkey operation.
3. Check P13–12 for +5.2 Vdc. If the voltage is not present, refer to “Power
Supply Troubleshooting” on page 37 for troubleshooting.
4. Press the Frequency hardkey on the front panel.
5. Using an oscilloscope, monitor P13–14 and P13–10 while rotating the RPG
knob. The LCD frequency value should change, and both signals at P13
should pulse to a TTL high. If either signal does not pulse, replace the
A1 Keyboard.
6. If the signals pulse at P13, check the signal at P221 pins 57 and 17 of the
motherboard. If the signals pulse at P221, replace the CPU board.
Symptom: Screen saver not working properly
The screen saver delay can be set for any integer from 1 to 12 hours. The CPU
board controls the screen saver by pulling the LIGHT_EN line low.
1. If the delay time elapses and the display does not go dark, check the
LIGHT_EN signal at P12–3.
— If the signal is a TTL low, replace the dc to ac inverter.
2. If the signal is a TTL high, check it at P221–16 of the motherboard.
— If the signal is high at P221, replace the CPU board.
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