32 E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Troubleshooting Assembly–Level Problems
— If the 5.2 Vdc line is bad, refer to “Power Supply Troubleshooting”
on page 37.
— If either the LIGHT_EN or VDISP are bad, check them at P221−16
and P221−55 respectively on the A31 Motherboard. If either signal
is bad at P221, replace the A18 CPU.
— If all the above signals are good, check the output of the dc to ac
inverter as follows:
a. Remove the front panel from the frame, and lay the front
panel face down.
b. With CN2−1 open, there is typically a 160 Vrms 40 kHz
signal. If not, replace the dc to ac inverter.
If the signal is there, replace the LCD.
Symptom: Bright display without characters
1. Ensure that the front–panel green power on LED is on. If not, refer to
“Power Supply Troubleshooting” on page 37.
2. Try adjusting the contrast controls.
3. Check the connection of the ribbon cable at J9 of the power switch/flat
panel interface board.
4. If the display is still too bright, use an oscilloscope to check P11 of the A31
Motherboard for the following signals:
P12−4 VDISP Brightness = 50, VDSP < 50 mV
Brightness = 1, VDSP = 3 Vdc
Signal State
Signal State
P11−4 VLCD
approximately 19.5 to 21 Vdc
a
P11−6 LCD_ENABLE_H >3 Vdc
P11−9, 10, 12, 13, 15, 16, 18, 19, 21, 22, 24, 25, 27, 28, 30, 31, 33,
34, 36, 37, 39, 40
Refer to Figure 1-1.
a. If >21V check the power supplies. If the power supplies are good, replace the mother-
board.
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