Nokia 7250, 7250i Instruction De Maintenance

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Apply –90dBm
1842.86771MHz signal
from generator to anten-
na connector

Oscilloscope at RX_I
Signal 140mVpp
DC offset 1.35V ***
Frequency 67.7kHz

Change ge-
nerator level
to –50dBm

Spectrumanalyzer
Antenna switch out-
puts, 
 1800 LNA out
–61 dBm

Spectrumanalyzer

Antenna Swithc input

-84 dBm

GSM1800 RX chain
functional

Oscilloscope
VR1,3...6   2.7V
Check HELGA serial
interface
(burst mode)

Check  C838, C839,
L821. L 872, 
C836, C837,
V801

Oscilloscope
VANT_1...3 0V

Oscilloscope
Check HELGA se-
rial interface (burst
mode)

Check HELGA
N600

Check Base-
band

* Spectrumanalyzer
reading with 1 kohm
passive probe (right val-
ue add +26 dB)

All spectrumanalyzer reading
values are measured with 1
kohm passive probe (use
tweezers to connect  the
probe ground  to the nearest
PWB ground). Reading value
is represented without +26
dB compensation.

Check C831,
L811

Check Antenna
Switch Z800

Spectrumanalyzer
HELGA inputs 
GSM 1800
–88 dBm

Check Base-
band

No

Synthesiszer trou-
bleshooting

Spectrumanalyzer
4G VCO out
3769.6MHz

∼

–30 dBm (*

Yes

Check HELGA
N500

* ** DC–level of RXI/RXQ in
continuous mode will decrease
slowly.
The original level can be resto-
red by rewriting gain set.