Ericsson GF 768 Troubleshooting Manual page 33

4/00021-2/FEA 209 544/6 C
6.4.2 Doesn't consume any current when On/Off key is pressed.
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.
Give the board power and start it up by pressing the On/Off key (in the fixture or in the back cover with a dummy
battery inserted, mount system connector to make the board lie steady in the back cover).
Check the current consumption.
• If the phone still doesn't consume any current, measure the resistance from the unmarked side of the "No"
keypad (fig. 6.10) to V702 pin 2 (fig. 6.3, ~0 ohms) and from V702 pin 3 to N702 pin 3 (fig. 6.3, ~0 ohms).
• If the resistance is too high there's a foil damage and the phone is to be discarded.
• If the resistance is correct, replace V702.
If the fault remains, send the phone to the next level.
6.4.3 Consumes more than 200mA.
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.
Check VDIG, VANA and VDSP (~3.2V, figs 6.3, 6.4 and 6.6).
• If any of the voltages are too low, measure the resistance from it to ground (VDIG - >500 ohms, VANA - >25
kohms, VDSP - >25 kohms).
• If the resistance is correct, replace the corresponding regulator (VDIG – N702, VANA – N700, VDSP –
N701, all class A). The VDSP regulator can only be replaced at this level if the circuit board is a 2/ROA
119 3283/7 R2A. At the other boards it's placed under the DSP shielding and the phone must be sent to the
next level to be repaired.
• If the resistance is too low there's a short circuit in one of the circuits that are fed by the corresponding reg-
ulator. Send the phone to the next level.
• If any of the voltages are too 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 resistance is correct, replace the corresponding circuit (VRAD – N453, VRPAD – N452, both of
class A). If the resistance from VVCO to ground is incorrect, the phone must be sent to the next level since
the VVCO regulator is placed under the large radio shilding. Usually it's the VRAD regulator (N453)
that's broken. The output voltage of it is then usually ~3V and it consumes a lot of current.
• 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.
Measure the resistance from VBATT to ground (>200 kohms).
Fig. 6.10
Troubleshooting guide
33