Ericsson PF 768 Troubleshooting Instructions page 17

PF768, Standard Electrical Repairs
Also note that the measuring point for VVCO is under the big radio shielding
(E202) and therefore you have to measure the voltage carefully through one of the
holes with a thin and preferably isolated probe as in fig. 3.6.
• If the VRAD or VVCO voltage is incorrect, send the phone to the next level.
• If the VRPAD voltage is too low, measure the resistance from it to ground (>25
kohms).
* If the resistance is correct, replace N452 (class A)..
* If the resistance is too low there's a short circuit in one of the circuits fed by
the regulator. Send the phone to the next level.
• If the VRPAD voltage is too high, replace N452.
Measure the resistance from VBATT to ground (>200 kohms, fig. 3.1).
• If the resistance is too low there's a short circuit in one of the circuits fed by
VBATT. Send the phone to the next level.
If the fault remains, send the phone to the next level.
3.4.4 The phone runs as long as the On/Off key is
pressed.
Open the phone and check for liquid damages.
Make sure the battery and system connector pads aren't dirty, liquid damaged or
oxidised.
Place the board in the fixture. Keep the board running by keeping the On/Off key
pressed.
Measure the voltage at C692 (~3.1V, fig. 3.3).
• If there is voltage, make sure pin 119 of D600 is correctly soldered.
* If the soldering is correct, replace D600 (class B, fig. 3.2).
• If there is no voltage at C692, measure the resistance of C692 (class A, >200
kohms).
* If the resistance is too low, replace C692 and check the voltage again.
* If the resistance is correct, check the voltages at N706 (fig. 3.8). VBATT at
pin 2, ground at pin 1 and the output voltage (~3.5V) at pin 3.
* If VBATT or ground is missing there's a foil damage and the phone is to
be discarded.
* If VBATT and ground are correct but not the output voltage, replace
N706.
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