Ericsson GF 768 Troubleshooting Manual page 35

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6.4.4 The phone runs as long as the On/Off key is pressed.
Open the phone and check for water damage.
Make sure there aren't water damage, dirt or oxidation at the battery or system connector pads.
Mount the board in the fixture, start it up and keep it running by keeping the On/Off key pressed.
Measure the voltage at C692 (~3.1V, fig. 6.3).
• If there's voltage, make sure soldering at D600 pin 119 is correct.
• If the soldering is correct, replace D600.
• If there's no voltage, measure the resistance of C692 (class A, >200 kohms).
• If it's too low, replace C692 and check the voltage again.
• If the resistance is correct, check the voltages at N706 (fig. 6.9). That is VBATT at pin 2, GND at pin 1 and
the output voltage (~3.5V) at pin 3.
• If VBATT or GND is missing there's a foil damage and the phone is to be discarded.
• If VBATT and GND are correct but not the output voltage, replace N706 (class A).
• If the output voltage is correct, measure the VRTC voltage at the positive side of the backup capacitor,
C720 (~3.1V, class A, fig. 6.9).
• If there's no voltage, replace V711 (class A, fig. 6.9).
• If the voltage is correct, measure the resistance from the positive side of C720 (fig. 6.9) to the
marked side of C692 (fig. 6.3, ~0 ohms).
• If the resistance is to high there's a foil damage and the phone is to be discarded.
If the fault remains, send the phone to the next level.
6.4.5 Doesn't start in the flash programmer.
Open the phone and check for water damage.
Make sure there aren't water damage, dirt or oxidation at the battery or system connector pads.
Mount the board in the fixture. Start it up and keep it running by keeping DCIO high.
Measure VANA and VDIG (~3.2V, fig. 6.4 and 6.3).
• 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 corresponding regulator (VDIG – N702, VANA – N700, both of
them class A).
• If the resistance is too low there's a short circuit in one of the circuits fed by the corresponding regulator. In
that case, send the phone to the next level.
• If any of the voltages are to high, replace the corresponding regulator.
Check power reset at C710 (fig. 6.3, >3V).
• If the voltage is too low, replace C710 (class A) and try again. If that doesn't help, replace N703 (class A, fig.
6.3).
Check VRAD (fig. 6.9, ~3.8V), VVCO (fig. 6.4, ~3,8V, measure through one of the holes in the shielding using a
thin probe (preferably isolated) as in fig. 6.5) and VRPAD (fig. 6.4, ~3.8V).
• If any of the voltages are too low, measure the resistance to from it ground (all should be >25 kohms). If it's
the VVCO voltage that's too low, send the phone to the next level as it can't be repaired at this level
• If the resistance is correct, replace the corresponding circuit (VRAD – N453, VRPAD – N452, both of
class A).
• If the resistance is too low there's a short circuit in one of the circuits that the regulator is feeding. Send
the phone to the next level.
• If any of the voltages are too high, replace the corresponding regulator.
Measure the amplitude of the 13MHz master clock at C680 (class A, >0.6V t-t, fig. 6.4).
• If the signal at C680 is too low, send the phone to the next level.
Make sure there's no faulty solderings at D600, D610 and D620 (fig. 6.2).
• If the solderings look good, replace D610 (class A).
• If that doesn't help, replace D600 (class B) first and then D620 (class A). Don't replace any circuit unless
Troubleshooting guide
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