Does Gsm Pa (N7502) Get Correct Bias Currents? Is The Level Of Bias Currents Ok; Are Tx-Iq Signals Ok - Nokia RM-57 Service Manual

Appendix A: RF Troubleshooting

3.4.2 Does GSM PA (N7502) get correct bias currents? Is the level of bias currents ok?

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 GSM850/EGSM900 and "0" in GSM1800/GSM1900)
• Measurements can be done with an oscilloscope and a VOLTAGE probe.
GSM850/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 4.6.4 when measured with an oscilloscope and a probe. Check 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 "Icont_31/Icont_32 (DC Offset 1.2 V)"
Check both currents.
3.4.2.1 Vinku (N7501) RB_EXT voltage ok?
• See section
3.4.2.2 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.
3.4.2.3 Replace Vinku (N7501)

3.4.3 Are TX-IQ signals ok?

• These current mode signals are not possible to measure, but are tested with self-tests. So if
there is no fail in 2.3 "ST_CDSP_TX_IQ_TEST" these signals should be ok. Otherwise Vinku
(N7501) or RAP3G (D2800) is faulty. Notice that it is not possible to replace RAP3G ASIC.
A-66
"Vinku (N7501) RB_EXT voltage ok?"
Icont_32 missing – C7561 short-circuited?
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when measured with an oscilloscope and a probe.
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