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CONFIDENTIAL 1 (3)
Nokia Mobile Phones Service Bulletin No. SB-029/25.04.01
Technical Support, Europe & Africa
NHM-5
BROKEN C508
If the end user complains of following symptoms:
- dropped calls
- no service
- poor downlink audio
- poor performance in weak fields etc
and then in service point following symptoms can be found:
- the phone may have difficulties to make location update/go in to service
on GSM tester, if the RF level is low
- RX sensitivity is very poor
- the BER can be alternating between very high % and 0%, if RF level is
below -65dBm
- the problem can be seen in both GSM900 and GSM1800 bands
it is likely that C508 (4x100 nF capacitor array 0508) is broken and needs to
be changed.
ITEM CODE DESCRIPTION
C508 2315105 CHIP ARRAY X5R 4X100N M 10V
Verification
It is simple to verify if broken C508 causes the problem by measuring the
RX I and Q signals with oscilloscope. Oscilloscope should be set to 1ms/div
and 500mV/div and appropriate Probe should be used. Note: It is not
recommended to use a simple Voltmeter to do this verification.
Test points
The RX I and Q signals can be measured on PWB in two ways, on the
topside (component side) and on the bottom side (keypad side)
NHM-5 SB-029
CONFIDENTIAL 2 (3)
Top side
Bottom side
The two vias highlighted in above picture can also be measured from the
bottom side of the PWB. (In this case it is not necessary to remove the
shielding can lid, but the lightguide can not be used)
Measurement procedure
1. Place the PWB in MJS-19 Module Repair Jig
2. Turn the phone on and set it to local mode with WinTesla
3. Select RX BURST mode in RF controls menu. No external signal is
needed
4. Measure RX I and Q signals with Oscilloscope
NHM-5 SB-029
CONFIDENTIAL 3 (3)
Measurement reference
In case that C508 is not faulty both RX I and Q signals should look like the
following picture
In case that either RX I or Q or both signals looks like the below picture,
C508 is broken and should be replaced.
NHM-5 SB-029