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3.1.1.3.1.3 Replace inductor L7516
•
If replacing does not help, replace GSM PA (N7502)
3.1.1.3.2 Are bias currents coming correctly to the GSM PA (N7502)?
EGSM: Icont_21 and Icont_22
GSM1800/GSM1900: Icont_31 and Icont_32
•
GSM transmitter has to be active before measurements. Procedure is explained in section
"Transmitter troubleshooting".
•
Set TX power level to the maximum ("5" in EGSM900 and "0" in GSM1800/GSM1900)
•
Measurements can be done with an oscilloscope and a VOLTAGE probe.
•
EGSM900:
Connect the probe to C7545 or C7544. Notice: C7544 is a non-assembled component so the probe
-
should be connected to the pad that can be still found from the PWB.
Typical full TX power bias currents (Icont_21 and Icont_22) should look somehow similar to figure
-
6.5.4 "lcont_21/lcont_22 (DC offset 1.2V)"
both currents.
•
GSM1800 or GSM1900:
Connect the probe to C7561 or C7556. Notice: C7556 is a non-assembled component so the probe
-
should be connected to the pad that can be still found from the PWB.
Typical full TX power bias currents (Icont_31 and Icont_32) should look somehow similar to figure
-
6.5.5 when measured with an oscilloscope and a probe. Check both currents.
3.1.1.3.2.1 Vinku (N7501) RB_EXT voltage ok?
•
See section
3.1.1.3.2.2 Are capacitors in GSM PA (N7502) bias lines working correctly?
EGSM: Icont_21 missing – Replace Vinku
Icont_22 missing – C7545 short-circuited?
GSM1800/GSM1900: Icont_31 missing – C7556 short-circuited?
•
Check that components are in place and solder joints are ok
•
Disconnect the power supply from the phone and use an ohmmeter to check that capacitors are
not short-circuited. If short-circuit is found replace capacitors mentioned above. If this does not
help go to the next step.
3.1.1.3.2.3 Replace Vinku (N7501)
A-34
"Vinku (N7501) RB_EXT voltage ok?"
Icont_32 missing – C7561 short-circuited?
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when measured with an oscilloscope and a probe. Check
Appendix A: RF Troubleshooting
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