Nokia Customer Care
6b - RF Troubleshooting
Company Confidential
RH-29
Issue 1 05/2004
Copyright
©
2004 Nokia Corporation
Page 5
Company Confidential
Troubleshooting chart for GSM1800 transmitter
If the Tx output is too high, then it is most likely that there is a problem within the Power
Control loop.
Mjoelner is receiving the Reference TXC from Baseband and not getting any feedback
from DET to compare with TXC. The result is that Mjoelner drives VDP_900/VPD_1800
high to try and increase the power output so that the DET signal is matching TXC. With a
break in the Power Control loop, the DET signal never reaches Mjoelner so it assumes
that the PA is not outputting enough power so it tries to compensate by increasing the
gain.
When checking the Power Control loop, make sure that VBD is pulsing at 2.8V Peak to
Peak. Check the DET pulse at Mjoelner input on R706.
START
Is TX Signal at
DCS / PCS In on
R819 OK?
Is signal on
C823 OK?
Is VPD_1800
signal OK?
Replace PA
Investigate
Mjoelner
Is signal at
DCS / PCS
Input of Z601
OK?
Replace
L801
Are Z601
Control lines
as per table?
Check RF
Connector
X602. OK?
Replace
Antenna
Switch
Replace RF
Connector.
Is TX Signal
at L705 OK?
Are TX I & Q
Signals OK?
Are TXP &
TXC OK?
Change
UEM
Change
UPP
TXC
U/S
TXP
U/S
Are Digital
I & Q Signals
OK at J213 &
J214
Is Vr2 2.8V
on R720?
Refer To Baseband
Fault Finding
Check T701
& Associated
Components.
YES
NO
YES
NO
YES
NO
NO
YES
NO
NO
YES
NO
YES
NO
YES
NO
YES
YES
YES
YES
NO
Test With
Spectrum
Analyzer
Test With
Oscilloscope
Check /
Inspect
End
Action
KEY
START
Is TX Signal at
DCS In on
L812 OK?
C650.
C650.
J202
and J203?
DCS
Check