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The voltage at point C will be the voltage at point B minus the voltage drop over the diode
between B and C.
The capacitor at point C, connected to ground, stores the voltage to maintain a constant level of
the voltage.
To be able to regulate VLCD exactly, is it fed back to an ADC transformer in N800.
The transformer does not measure the voltage VLCD directly, since the ADC transformer only
handles positive voltage, therefore is it transformed into VLCDMEAS.
VLCDMEAS is achieved by a voltage divide between VLCD and VDIG.
VLCD is compensated using values from EEPROM, since the LCD display is temperature
sensitive.
23.2 Type of fault
Attach a dummy or a fully charged battery, connect the system connector and start the phone in
the test program.
Go to MMI \ Display / Top.
Click on "Chess pattern" to se the test pattern in the display.
Click on "Inv. Chess pattern" to make an inventory of the pattern.
If the display shows all segments in both cases mentioned above and the contrast is correct, the
fault probably is without fault.
If the phone does not start, go to chapter "Enter test program"-fault.
If the display misses one or more segments, go to section 23.3.
If the display does not show anything at all, go to section 23.4.
If the display has got bad contrast or is completely black, all segments are lit, go to section 23.5.
23.3 One or more segments are missing
Open the phone and check for water damages.
No further action should be taken for a liquid damaged telephone.
Replace the display assy. according to the mechanical repair guide.
Try the phone again according to section 23.2.
4/00021-3/FEA 209 544/18 B
Fig. 23.5
Trouble Shooting Guide, Advanced
102(121)
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