Ericsson GF 768 Troubleshooting Manual page 36

Troubleshooting guide
you've verified that the amplitude of the master clock is correct. Try programming the phone after
every component replaced.
If the fault remains, send the phone to the next level.
6.4.6 Is programmable but doesn't start afterwards or is troublesome 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 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 the
VVCO voltage is too low, send the phone to the next level.
• If the resistance is correct, replace the corresponding circuit (VRAD – N453, VRPAD – N452, all 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.
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). Try programming the phone
after every component replaced.
If the fault remains, send the phone to the next level.
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