Ericsson GF 768 Troubleshooting Manual page 25

4/00021-2/FEA 209 544/6 C
• If it's correct, replace V706 (class A).
Measure the resistance from H600 pad 1 to V606 pin 3 (~0 ohms, fig. 5.2).
• If it's too high there's a foil damage and the phone is to be discarded.
• If it's correct, check the soldering at D600 pin 91 (fig. 5.3). If the soldering is correct, replace R651 (class A,
fig. 5.3) and V606 (class A, fig. 5.2). If that doesn't help, replace D600 (class B, fig. 5.3).
If the fault remains, send the phone to the next level.
5.3 The background illumination for the display isn't lit or is faintly glowing.
Open the phone and check for water damage.
Make sure all the LEDs (H651-H654, all of them class A, fig. 5.1) are mounted and correctly soldered.
Give the board power and start it up. If a few but not all of the LEDs aren't lit, replace them.
If none of the LEDs are lit, measure the resistance of one of them.
• If the resistance is ~0 ohms there's a short circuit in at least one of the LEDs. Remove on LED at a time. Mea-
sure the resistance after every LED removed. When the resistance goes up the problem is solved.
• If the resistance is higher than 0 ohms, make sure there is VBATT voltage at the marked side of the LEDs (fig.
5.1).
• If VBATT is missing there's a foil damage, likely caused by water damage, and the phone is to be dis-
carded.
• If VBATT is correct, make sure that R612 (~0 ohms), R610 (~33 ohms) and R611 (~0 ohms, all of them
class A, all in fig. 5.4) are mounted and have the correct resistance.
Table 5.1 shows the symptom when the resistors are of incorrect resistance.
Missing or broken
R609
R610
R611
R612
Fig. 5.4
H651-H654 H655-H660
Lit
Not lit
Faintly glowing
Not lit Faintly glowing
Not lit
Lit
Not lit
Troubleshooting guide
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