Nokia 7250, 7250i Service Manual

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Synthesizer

troubleshooting

Synthesizer
OK

Yes

*(When 2.5kOhm passive probe is used,
correct the measurement by +34 dB

Replace
VCO

Replace
faulty
component(s)

Yes

Set with RF controls:
Active Unti = Rx
Operation mode = Continuous

Check with RF probe:
-4G VCO out signal
- 3589.6 MHz (GSM900)
-3495.6 MHz (GSM1800)
- 3760 MHz (GSM1900)
Level >-10dBm (*

OK ?

VCO out signal level<-10dBm

Check balun
output levels and
solder joints
OK ?

Check output signal on
1 GHz span
Signal found on
incorrect frequency ?

Check with oscilloscope:

-4G VCO Vcc = 2.7V

OK ?

Baseband
troubleshooting

Check with oscilloscope:

VCO control voltage

from VCO pin

0V ?

>4.0 V ?

Replace
VCO

Check balun
output levels and
solder joints
OK ?

Check VCO control
loop components

OK ?

Replace
faulty
component(s)

Yes