Ericsson GF 768 Troubleshooting Manual page 26

Troubleshooting guide
Table 5.1
If none of the LEDs, H651-H654 and H655-H660, are lit, measure the voltage at the marked side of R607 (~3.1V,
fig. 5.4). Before measuring you have to press a key for the processor to set the LED3K signal high for
about 10s.
• If the voltage is missing, check the soldering at D600 pin 92 (fig. 5.3). If it's correct, replace D600 (class B).
• If the voltage is correct, replace R607 (class A).
If the fault remains, send the phone to the next level.
5.4 The background illumination for the keyboard is missing or faintly glowing.
Open the phone and check for water damage.
Make sure all of the LEDs, H655-H660 (all of them class A, all in fig. 5.1), are intact, mounted and correctly sol-
dered.
Give the board power and start it up. If a few but not all of the LEDs doesn't light up, replace them.
If none of the LEDs are lit, check for VBATT voltage at the marked side of the LEDs.
• If VBATT is missing there's a foil damage, likely caused by water damage, and the phone is to be discarded.
• If VBATT is correct, measure the resistances of R612 (~0 ohms), R610 (~33 ohms) and R611 (~0 ohms, all of
them class A, all in fig 5.4. Table 5.1 shows the symptom when the resistors have incorrect resistance.
If none of the LEDs, H651-H654 and H655-H660, are lit, measure the voltage at the marked side of R607 (~3.1V,
fig. 5.4). Before measuring you have to press a key for the processor to set the LED3K signal high for about
10s.
• If the voltage is missing, check the soldering at D600 pin 92 (fig. 5.3). If it's correct, replace D600 (class B).
• If the voltage is correct, replace R607 (class A).
If the fault remains, send the phone to the next level.
5.5 Green top indicator doesn't work.
Open the phone and check for water damage.
Make sure the double LED, H650 (class A, fig. 5.2), isn't incorrectly soldered. If the solderings are correct, give
the board power and start it up.
Measure the voltage at H600 pad 4 (~3.4V, fig. 5.2).
• If the voltage is missing, measure the VRPAD voltage (3.8V) at V706 pin 2 (class A, fig. 5.2).
• If VRPAD is missing at V706 pin 2, check if there's VRPAD at N452 pin 5.
• If it's incorrect or missing at N452 pin5, go to chapter 6.
• If it's correct, measure the resistance from N452 pin5 to V706 pin 2 (~0 ohms, figs 5.3 and 5.2). If it's
too high there's a foil damage and the phone is to be discarded.
• If there is VRPAD voltage at V706 pin 2 and it's correct, measure the resistance from VBATT to V706 pin
3 (~0 ohms, figs 5.3 and 5.29.
• If it's too high there probably is a foil damage between VBATT and V706 pad 3 and the phone is to be
discarded.
• If it's correct, replace V706 (class A).
Check the soldering at D600 pin 94.
If the fault remains, send the phone to the next level.
5.6 Green top indicator doesn't work.
Open the phone and check for water damage.
Make sure the double LED, H650 (class A, fig. 5.2), isn't incorrectly soldered. If the solderings are correct, give
the board power and start it up.
Measure the voltage at H600 pad 4 (~3.4V, fig. 5.2).
• If the voltage is missing, measure the VRPAD voltage (3.8V) at V706 pin 2 (class A, fig. 5.2).
• If VRPAD is missing at V706 pin 2, check if there's VRPAD at N452 pin 5.
• If it's incorrect or missing at N452 pin5, go to chapter 6.
• If it's correct, measure the resistance from N452 pin5 to V706 pin 2 (~0 ohms, figs 5.3 and 5.2). If it's
too high there's a foil damage and the phone is to be discarded.
• If there is VRPAD voltage at V706 pin 2 and it's correct, measure the resistance from VBATT to V706 pin
3 (~0 ohms, figs 5.3 and 5.29.
26
4/00021-2/FEA 209 544/6 C