Keysight Technologies E8257D Service Manual page 32

Troubleshooting
Troubleshooting Assembly–Level Problems
Symptom: Bright display without characters
1. Ensure that the front–panel green power on LED is on. If not, refer to
2. Try adjusting the contrast controls.
3. Check the connection of the ribbon cable at J9 of the power switch/flat
4. If the display is still too bright, use an oscilloscope to check P11 of the A31
Signal
P11−4 VLCD
P11−6 LCD_ENABLE_H
P11−9, 10, 12, 13, 15, 16, 18, 19, 21, 22, 24, 25, 27, 28, 30, 31, 33,
34, 36, 37, 39, 40
a. If >21V check the power supplies. If the power supplies are good, replace the mother-
board.
32
Signal
P12−4 VDISP
— If the 5.2 Vdc line is bad, refer to
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.
"Power Supply Troubleshooting" on page
panel interface board.
Motherboard for the following signals:
E8257D/67D, E8663D PSG Signal Generators Service Guide
State
Brightness = 50, VDSP < 50 mV
Brightness = 1, VDSP = 3 Vdc
"Power Supply Troubleshooting"
37.
State
approximately 19.5 to 21 Vdc
>3 Vdc
Refer to
a
Figure 1-1.