RM-12
Nokia Customer Care
Issue 1 11/2004
COMPANY CONFIDENTIAL
68
Copyright © 2004 Nokia. All Rights Reserved.
Backlight troubleshooting (2)
Start
Check VBAT availability through
current path from following points.
1. L4426
2. C4420 & C4421
3. R4423 & L4421 & V4420
4. C4443 & C4424
5. L4422 & C4428 & C4429 & C4425 & R4430
D4420 pin #8 = 0V
Backlight OK?
Replace series components
before point where VBAT
voltage is lost. Start from battery
side VBAT.
Check also C4423 and
R4446 (value = 27R) soldering.
Check X4421 pin soldering.
C4425 =
VBAT?
No
PWB failure
Disable backlight
from Control Panel
Enable backlight
from Control Panel.
Full brightness
Yes
D4420 pin #8
= 2.78V
Use partial mode or
adjust brightness period
to lowest value to disable
display backlight. Verify
functionality with working
display unit.
Yes
No
Replace D4420.
Check also with
another display unit
after component
change.
END
Backlight OK?
Yes
END
No
PWB failure