Ericsson PF 768 Troubleshooting Instructions page 20

PF768, Standard Electrical Repairs
3.4.6 Able to program the phone but it doesn't start
afterwards or it is troublesome in the flash pro-
grammer.
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 DCIO high.
Check the VANA and VDIG voltages (~3.2V, fig. 3.4 and 3.3).
• 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 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.
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 the 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.
• f the VRPAD voltage is too high, replace N452.
Make sure there aren't any faulty solderings at D600, D610 or D620 (fig. 3.2).
• If they look ok, replace D610 (class A).
* If that doesn't help, replace D600 (class B) first and then D620 (class A) if
that doesn't help. Try programming the phone in the flash programmer after
every circuit replaced.
If the fault remains, send the phone to the next level.
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