LG KF390 Service Manual page 88

In depth troubleshooting sequence for an initial PM6658 power-up is listed below:
1. Apply the external supply voltage (perhaps a wall charger); verify its voltage at PM6658 pin C1
(VCHG).
2. Check the handset's primary power supply voltage (VDD) at all the key points:
a. Appropriate PM6658 VDD pin numbers; this set of pins depends upon whether subregulation is
used or not. The complete list of possible VDD pins: A11, B2, B3, B9, H11, K10, L5, and L7.
b. PM6658 VDD detection input, pin D1 (ISNS_M)
c. Battery transistor (source pin)
d. VREG_5V inductor
3. Check the internal reference voltage by probing PM6658 pin C11 (REF_BYP)
→ 1.25V( acceptable offset error voltatge 2% )
4. Check the pass transistor's control voltage - PM6658 pin C2 (CHG_CTL_N).
5. Check the keypad power signal at pin L4 (KPD_PWR_N) - it should be pulled up to an internal
supply voltage. This pin should measure approximately +2.8 V.
Other Cases that classfied Power-on trouble are below:
1. Pernamently reset occur when Touch IC( U501) was damaged → Change the SUB Board or Touch
IC(U501)
2. In Case of Display Problems → Check Display troubleshooting
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4. TROUBLE SHOOTING
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