Ericsson GF 768 Troubleshooting Manual page 17

4/00021-2/FEA 209 544/6 C
Pad # Name
1 2
I C-CLOCK
2 GND
3 VDIG
4 VLCD
5 2
I C-DATA
Table 3.2
• If there isn't VLCD voltage at pad 4, measure the resistances from the pad to V608 pin 2 (~0 ohms) and from
pad 2 to GND (~0 ohms). If any of the resistances are too high there's a foil damage and the phone is to be dis-
carded.
2 2
If I C-DATA or I C-CLOCK voltage is missing, check VDIG at C600 (~3.2V, fig. 3.5).
• If VDIG is incorrect, go to chapter 6.
• If VDIG is correct, measure the resistance of R619 (class A, 2.2 kohms, fig. 3.5), R620 (class A, 2.2 kohms,
fig 3.5), R615 (class A, 10 kohms, fig. 3.6) and R616 (class A, 10 kohms, fig. 3.6). Make sure the solderings at
D600 pads 3 and 4 (fig. 3.1) are correct.
• If the resistances and the solderings are correct, replace D600 (class B).
3.4 The display is completely black.
Open the phone and check for water damages.
Give the board power and start it up with the display mounted by pressing the On/Off key. If the phone turns itself
off after a few seconds, keep it running by keeping DCIO high.
Check the VDIG and VANA feed voltages (~3.2V, fig. 3.2 or 3.5).
• If any of the voltages are too low, measure the resistance from it to ground (VDIG>500 ohms, VANA>25
kohms).
• If the resistance is correct, replace the correspondings regulator (VDIG - N702, VANA - N700, both of
class A).
• If the resistance is too low there's a short circuit in one of the circuits fed by the corresponding regulator. If
that's the case, send the phone to the next level.
•If any of the voltages are too high, replace the corresponding regulator.
If the fault remains, go to 3.1 or 3.2.
Voltage
~3.2V
0V
~3.2V
~-5V
~3.2V
Fig. 3.6
Troubleshooting guide
17