Ericsson T28S Troubleshooting Manual page 18

Measure the voltages on the display pads (H623).
Pad 1: VLCD
Pad 2: VDIG
Pad 3: I
Pad 4: Gnd
Pad 5: I
If I2CDAT or I2CCLK voltage is missing, check the VDIG voltage (2.75 V).
If the VDIG voltage is incorrect, go to chapter 3 ("On/off problems").
If the VDIG voltage is correct, measure the resistances of R619 (6.8 kohms), R620 (6.8
kohms), R615 (0 ohm) and R614 (0 ohm).
If any of the resistances are incorrect, replace the corresponding resistor.
If there is no VLCD voltage, check the resistance from pad 1 of H623 to pin 2 of V608 (0
ohm).
If the resistance is incorrect there is a foil damage, send the unit on according to the local
company directives.
If the fault remains, send the unit on according to the local company directives.
5.2 Background light and LED
Insert a dummy battery and a SIM-card into the phone and start it up by pressing the On/Off
key.
If the background illumination does not light up at start, go to section 5.2.1.
Wait for the phone to get SERV (towards the test instrument or the net).
If the top indicator does not start to flash green when the phone has got SERV, go to section
5.2.2
When the phone has got SERV and the top indicator flash green, reduce the battery voltage to
3.2V. By doing that the top indicator should start to flash red, the battery indicator show an
empty flashing battery and the phone should warn with a beep.
If the battery indicator shows an empty flashing battery but the top indicator does not flash
red, proceed to section 5.2.2.
If none of the above mentioned things happen the phone needs a battery calibration.
Send the unit on according to the local company directives.
5.2.1 Background illumination glows faintly or does not work at all
Use the menu to set the light on (Settings/Profiles/Edit Profiles/Light/On).
Open the phone and check for liquid damage.
Wash around X750 if needed (Fig.5.1).
Replace the illumination panel.
4/00021-2/FEA 209 544/19 E
5.90 – 6.20 V
2.75 V
2
CDAT 2.70 – 2.85 V
2
CCLK 2.70 – 2.85 V
Trouble Shooting Guide, Standard
18(29)