Troubleshooting: Display Faults
Issue 2
149
Part No. 306-0430-102
Display Faults
Backlight
WARNING – LETHAL VOLTAGES
A high AC voltage is present at the inverter and backlight.
Extreme caution is required when diagnosing failure in these areas.
Note: Some DVMs may not show the 1000 V AC correctly. Use an oscilloscope fitted with a high
voltage probe to measure the voltage.
Possible Cause Remedial Action
Backlight shut down by
screensaver facility
Press any key on the keypad to re-start the backlight.
Backlight inverter faulty
1
Check for 24 V DC at 3 way input connector on backlight converter
(Pins 1 and 2 on I/O board B/LIGHT connector).
2
Check for 1000 V AC at output leads from backlight inverter
(Pins 3 and 5).
3
If 24 V DC present but 1000 V AC missing, change the LCD/backlight
assembly (see
LCD and Backlight
, page 115).
Cable from I/O board to
backlight is disconnected or
faulty
1
If 24 V DC is not present at backlight inverter but is present at Pins 1
and 3 of B/LIGHT connector on I/O board, check that the cable is
connected between the two.
2
Check cable for continuity, replace if faulty.
Backlight faulty If 1000 V AC is present at output of backlight inverter but backlight not
illuminated, change the LCD/Backlight assembly (see
LCD and Backlight
,
page 115).
I/O or CPU board faulty
1
Check for 24 V DC on pins 1 and 3 of B/LIGHT connector on I/O board.
If voltage not present, change I/O board (see
I/O Board
, page 110).
2
If changing the I/O board does not clear the fault, change the CPU
board (see
CPU Board
, page 112).
Table 40 Display Backlight Failure
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