Keypad Backlight; How The Keypad Backlight Works; Keypad Backlight Troubleshooting - Nokia 3155i Troubleshooting Manual

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3155/3155i (RM-41), 3152 (RM-61)

Baseband Description and Troubleshooting

Keypad Backlight

Klight coming out of UEMEK controls the keypad backlight LEDs. Klight enables the LED

driver, which is a constant voltage supply for all the keypad LED in series. The current is

set for all the branches by Rset which in this case is 33k Ohms and equates to 10mA

through each LED.

When troubleshooting keypad backlight, make these common checks (see

Figure

24):

• Perform visual inspection of all the components including LEDs

• Check Vbat to make sure the driver has power

• Check Klight to make sure driver is enabled by the UEMEK. If not correct, check

the UEMEK.

• If lights are too dim or too bright, check Rset. Rset controls the current going

through the LEDs.

• Check Vout to make sure LEDs are getting power. If still not working, change

LED. Make sure LED orientation is correct.

Page 24

Figure 22: Keypad Backlight Diagram

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Figure 23

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ISSUE 1 07/2005

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