GH688,GA628, Standard Electrical Repairs
4/00021-2/FEA 209 544/1.G 17 (112)
3.4 Measuring at a powered circuit board.
3.4.1 Doesn’t start in the flash programmer.
Open the phone and check for liquid damage.
Make sure the system connector pads aren’t burnt.
Place the board in the fixture. Start it up and keep it running by keeping DCIO high.
Check VDIG and VDSP voltages (~3.2 V, fig. 3.2).
• If any of the voltages are too low, measure the resistance to ground (VDIG > 500
ohms, VDSP > 25 kohms).
* If the resistances are correct, replace the corresponding circuit (VDIG –
N702, VDSP – N701, both of class A).
* If the resistance is too low, send the phone to next level.
• If any of the voltages are too high, replace the corresponding circuit.
Check the power reset voltage at C710 (fig. 3.2, >3V).
• If it’s lower, replace N450 (class A, fig. 3.6) and try again.
* If it didn’t work, replace C710 (class A).
Fig. 3.6
Check VRAD, VVCO and VRPAD (~3.8V, fig. 3.6).
• If all three voltages are wrong, measure the resistance from N450 pads 8, 11, 12,
13 and 14 to ground (~0 ohms).
* If the resistance is too high there is a foil damage and the phone is to be dis-
carded.
* If it is correct, replace the circuit and eventually the transistors (V452,
V451 and V450, all of them class A).
• If one or two of the voltages are wrong, measure the resistance from the corre-
sponding voltage source to ground (>50 kohms).
* If the resistance is correct, replace the corresponding transistor.
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