Ericsson PF 768 Troubleshooting Instructions page 16

PF768, Standard Electrical Repairs
• If the phone still doesn't consume any current, measure the resistances from the
unmarked side of the "No" keypad (fig. 3.7) to pin 2 of V702 (~0 ohms, fig. 3.3)
and from pin 3 of V702 to pin 3 if N702 (~0 ohms, fig. 3.3).
Fig. 3.7
* If one or both of the resistances are too high there's a foil damage and the
phone is to be discarded.
* If the resistances are correct, replace V702 (class A).
If the fault remains, send the phone to the next level.
3.4.3 Consumes more than 200mA.
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 it running by keeping DCIO high.
Check the VDIG, VANA and VDSP voltages (~3.2V, fig. 3.3 and 3.4).
• If any of the voltages are too low, measure the resistance from it to ground
(VDIG>500 ohms, VANA>25 kohms, VDSP>25kohms).
* If the resistance is correct, replace the corresponding regulator (VDIG –
N702, VANA – N700, VDSP – N701, all of 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 any of the voltages are too high, replace the corresponding regulator.
Check the VRAD (fig. 3.1, P501 measuring point), VVCO (fig. 3.5) and VRPAD
(fig. 3.5) voltages (all of them ~3.8V).
Note that P501 is a calibration point. It is VRAD you measure but after 2 resistors.
The calibration point has the right voltage as long as the transmitter isn't activated.
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