Nokia 6255 Guide

Nokia Customer Care
6255/6255i/6256/6256i (RM-19)
Mobile Terminal
Issue 2 05/2005 Company Confidential ©2005 Nokia Corporation
RF Description and
Troubleshooting

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RF Description and Troubleshooting Nokia Customer Care
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Contents Page
Introduction ..................................................................................................................................................... 5
Mobile Terminal Components ..................................................................................................................... 6
Main PWB ......................................................................................................................................................6
UI (Secondary) PWB ....................................................................................................................................8
Preliminary RF Troubleshooting............................................................................................................... 10
Mobile Terminal Cannot Make a Call ..................................................................................................10
Tx Power Low ..............................................................................................................................................10
Transmitter RF Troubleshooting .............................................................................................................. 11
Transmitter Block Diagram .....................................................................................................................12
Transmitter Schematics ...........................................................................................................................13
Transmitter Troubleshooting Setup ......................................................................................................15
AMPS Tx Setup ....................................................................................................................................... 15
Cell Tx Setup ........................................................................................................................................... 18
PCS Setup................................................................................................................................................. 20
Transmitter RF Troubleshooting Procedures ......................................................................................22
Failed Test: Tx PA Detector ................................................................................................................. 23
Tx Output Spectrum.............................................................................................................................. 24
Tx DC Test Points - Bottom Side ....................................................................................................... 25
Tx DC and RF Test Points - Top Side................................................................................................. 26
Tx RF Test Points - Bottom Side........................................................................................................ 28
RF Power Supply DC Test Points - Bottom Side............................................................................ 29
Receiver RF Troubleshooting .................................................................................................................... 31
Receiver Block Diagram ...........................................................................................................................32
Receiver Schematics .................................................................................................................................33
RF AGC Status ............................................................................................................................................35
Turning on the Rx Path ............................................................................................................................36
Switching the Rx Gain States ................................................................................................................38
Checking AMPS from RF to IQ ........................................................................................................... 38
Checking Cell Receiver from RF to IQ.............................................................................................. 39
Checking PCS Receiver from RF to IQ.............................................................................................. 41
Receiver Diagnostic Signal Tracing ......................................................................................................42
Receiver DC Test Points........................................................................................................................ 43
Receiver RF Test Points ........................................................................................................................ 44
Receiver IF Test Points.......................................................................................................................... 45
Receiver Logic Input Voltages ................................................................................................................46
N7160 Receiver Overview .......................................................................................................................47
Synthesizer Troubleshooting .................................................................................................................... 49
Synthesizer Block Diagram .....................................................................................................................50
Synthesizer Schematics ...........................................................................................................................51
Synthesizer Troubleshooting Setup ......................................................................................................52
Incorrect PLL Frequencies.................................................................................................................... 52
VCTCXO Troubleshooting .........................................................................................................................53
VCTCXO Manual Tuning....................................................................................................................... 54
AFC Voltage Troubleshooting .................................................................................................................55
UHF Synthesizer .........................................................................................................................................56
UHF Synthesizer Test Points ............................................................................................................... 57
Rx VHF LO (N7100) Schematic ..............................................................................................................58

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Rx VHF LO Troubleshooting ....................................................................................................................59
Tx UHF LO (N7000) Schematic ..............................................................................................................60
Tx UHF LO (N7000) Troubleshooting ....................................................................................................61
GPS Troubleshooting................................................................................................................................... 62
GPS RF Block Diagram .............................................................................................................................62
GPS RF Schematic .....................................................................................................................................63
GPS Troubleshooting Setup ....................................................................................................................64
Self Test Failure...................................................................................................................................... 65
Oscillator Failure.................................................................................................................................... 65
CW Test Failure....................................................................................................................................... 65
GPS RF Troubleshooting....................................................................................................................... 65
GPS DC Test Points................................................................................................................................ 66
GPS RF Test Points................................................................................................................................. 69
FM Radio Troubleshooting ........................................................................................................................ 71
FM Radio Schematic .................................................................................................................................71
FM Radio Troubleshooting Setup ..........................................................................................................72
FM Radio Part Layouts and Probe Points........................................................................................ 72
Bluetooth Troubleshooting ....................................................................................................................... 75
Bluetooth Schematic ................................................................................................................................75
Bluetooth Troubleshooting Setup .........................................................................................................76
Bluetooth Troubleshooting Flowchart ............................................................................................. 77
Bluetooth DC and RF Test Points ...................................................................................................... 78

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Introduction
When troubleshooting the receiver, first check the RX_AGC PDM value. The AGC value
should be close to the typical values in the tables. The RX AGC tries to keep a constant
amplitude at the output of the receiver chain; if the AGC value indicates an AGC gain
that is substantially higher than normal, the AGC is compensating for extra loss in
another component. If the AGC PDM values are normal and there is still a problem, check
the actual AGC voltages. RF probing at specific locations in the chain can then help to
pinpoint the source of the problem.
Likewise, when troubleshooting the transmitter, first check the measured output power
and AGC values, which give an indication of where to start probing.
Although probing points and signal-level information are given for each point in the
receiver and transmitter chains, the troubleshooter is not expected to probe each point
on every mobile terminal — only the suspected trouble spots.
Absolute power measurements were made with an Agilent (HP) 85024A active high-
impedance probe. Other probes can be used (but should be high-impedance so that the
measurement does not load the circuit) but may very well have a different gain;
therefore, adjust the absolute measurements accordingly. Also, adjust if using a probe
attenuator.
Where a range is given for loss, typically the higher loss occurs at the band edges.
Probing is not a very accurate method to measure absolute power; therefore, you cannot
expect measured results to exactly match the numbers listed.
Power depends on the impedance of the circuit. For example, if a filter has a nominal loss
of 5dB, then straightforward probing on the input and output, then subtracting, might
not result in 5dB because the input impedance might be different from the output
impedance. Most components in the RF section have the same input and output
impedance (50ohms), but where this is not the case absolute power is noted in dBm,
rather than loss or gain in dB.
When testing the CDMA receiver, it is easier to inject a CW tone into the receiver. The
gains and losses are the same for a CW signal as for CDMA.
Note: After opening the shield lids, always replace them with new lids.

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Mobile Terminal Components
The mobile terminal includes two PWB boards, the main PWB and the UI PWB.
Main PWB
Following are the components of the main PWB.
Figure 1: Main PWB component layout - top
Tx power
detector
Tx I/Q signal
test points
Rx I/Q signal
test points

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Figure 2: Main PWB component layout - bottom
Antenna
connector
PCS PA
Cell PA
Cell Tx filter
PCS Tx filter
N7000:
Tx Upconverter
FM radio IC
Tomahawk
connector
Flash
D2800
processor
VCO
Diplexer
Cell duplexer
PCS duplexer
Synthesizer IC
Headset jack
Rx RF Cell filter
N7160:
Rx front-end
Rx RF PCS filter
Rx IF AMPS filter
VCTCXO
Rx IF CDMA filter
N7100:
Rx downconverter
UEM
Bluetooth IC
Cell coupler PCS coupler

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UI (Secondary) PWB
Following are the components of the UI PWB.
Figure 3: UI PWB component layout - top
GPS ceramic filter
GPS LNA
GPS SAW filter

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Figure 4: UI PWB component layout - bottom
GPS 16.368 MHz
TCXO
GPS antenna
matching circuitry
GPS ceramic antenna
GPS antenna
connector
GPS RF IC
GPS BB IC

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Preliminary RF Troubleshooting
The following sections identify steps to troubleshoot some common RF issues.
Mobile Terminal Cannot Make a Call
Verify the following if the mobile terminal cannot make a call:
1. The mobile terminal is in Normal Mode (i.e., the mobile terminal is searching for
a signal, net server is on).
2. The Preferred Roaming List (PRL) is loaded into the mobile terminal.
3. The mobile terminal is tuned and has passed tuning. Read the tuning parameters
using the Read Parameters component in Phoenix. An untuned mobile terminal
has all zeros in the tuning file.
4. The call box channel is set for a channel in PRL.
5. The SID is correct and entered into the mobile terminal.
6. The VCTCXO is centered as described in the "VCTCXO Manual Tuning" section on
page 54.
7. The transmitter and receiver are working properly in Local Mode. See
"Transmitter RF Troubleshooting" on page 11 and "Receiver RF
Troubleshooting" on page 31 for detailed information.
Tx Power Low
Complete the following steps if Tx power is low:
1. Use Phoenix to turn on the transmitter in Local Mode.
2. Perform a visual inspection of the PWB under a microscope to check for the
proper placement, rotation, and soldering of components.
3. Look for the presence of a Tx signal on a spectrum analyzer at the correct
frequency.
• If a signal is present but off-frequency, check the synthesizers for proper
frequency and amplitude. One of the synthesizers may be unlocked or the
VCO has no output signal.
• If a signal is not present or is present but is low in amplitude, check the
probing diagrams to determine where in the chain the fault occurs. (See "Tx
RF Test Points - Bottom Side" on page 28.)
4. Ensure that the power supplies to the Tx have the correct voltage. (See "Tx DC
Test Points - Bottom Side" on page 25)
5. Ensure that the AGC PDMs are set for the desired Tx power and that the AGC
voltages are correct. (See "AMPS Tx Setup" on page 15, "Cell Tx
Setup" on page 18, or "PCS Setup" on page 20.)

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Transmitter RF Troubleshooting
Following are the main Tx RF components.
Figure 5: Main transmitter RF components
Antenna
connector
PCS PA
PCS
duplexer
PCS
coupler
Cell
duplexer
Cell
coupler
Diplexer
Power
switch
Cell PACell Tx SAW filter
PCS Tx SAW filter
TOP SIDE BOTTOM SIDE
Power
detector

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Transmitter Block Diagram
Following is the block diagram for the Tx RF system.
Figure 6: Tx system block diagram
N7000 Tx IC

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Transmitter Schematics
The following schematics are for general reference only. See the Schematics chapter for detailed versions.
Figure 7: Transmitter schematic 1
N7000 Tx IC
Tx LO lock
voltage
Loop filter
Cell Tx filter
PCS Tx filter

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Figure 8: Transmitter schematic 2
PCS PA PCS duplexer
Diplexer
Couplers
PCS PA
Cell PA
Cell duplexer
Power detector
Component
changes based
on PA
manufacturer

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Transmitter Troubleshooting Setup
Use the following sets of procedures to troubleshoot the transmitter using Phoenix. Due
to the compact layout of the mobile terminal, some of the major test points are not
accessible without destroying the shield frames and the EL lamp. For example, duplexers/
diplexer/couplers test points are blocked by the test jig, the PA test points are
underneath the shield frame, and the BBIQ points are underneath the EL lamp.
To minimize effort, check the following in order:
1. Tx power at the RF connector.
2. All Tx DC points.
3. All soldering jig points for the whole Tx chain.
4. UHF LO presence:
• If the UHF LO is present, check the N7000 output.
• If the UHF LO is not present, it is a synthesizer problem.
5. If there is no N7000 output:
a. Change the N7000.
b. If the problem persists, reflow the duplexers, diplexer, and couplers.
c. If the problem persists, change the PA.
6. If there are several failed mobile terminals with the same symptoms, it may be
necessary to break one to determine the cause.
Use the following sections to set up troubleshooting in Phoenix according to the band
you are using:
• "AMPS Tx Setup" on page 15
• "Cell Tx Setup" on page 18
• "PCS Setup" on page 20
AMPS Tx Setup
Use the following procedures to prepare for AMPS Tx troubleshooting using Phoenix.
1. Connect the RF test connector to a spectrum analyzer.
2. Connect the mobile terminal to the PC via a test jig. (The bottom connector is a
USB port.)
3. Connect a power supply to the mobile terminal.
4. Open the Troubleshooting menu, and click Phone Control.
The Phone Control dialog box appears.

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5. Click the LOCAL button in the Phone State area to put the mobile terminal into
Local Mode.
Figure 9: Phone Control dialog box
6. Open the Troubleshooting menu, point to AMPS, and click AMPS Control.
The AMPS Control dialog box appears.
Figure 10: AMPS Control dialog box
7. Click the Tx Control tab.
8. In the Set Channel field, type 384.
9. In the Power Level field, type 5.
10. Select the Transmitter ON option, and click Execute.

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11. Configure the spectrum analyzer using the following values:
• Center Frequency = 836.52 MHz
• Span = 100 MHz
• Amplitude = 20 dBm
• Attenuation = Auto
• BW = Auto
Figure 11: RF PDM dialog box for AMPS
12. Click Read Phone to update the values.
Table 1: RF PDM Values at Power Level 5
Description/Field Reference Value
AGC1 -512
AGC2 -31
AGC3 -400
Rx IF AGC -234
AFC +176
Pout at RF connector +14dBm
Current 400-500mA

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Cell Tx Setup
Use the following procedures to prepare for Cell Tx troubleshooting using Phoenix.
1. Connect an RF test connector to a call box.
2. Connect the mobile terminal to the PC via a test jig. (The bottom connector is a
USB port.)
3. Connect a power supply to the mobile terminal.
4. On the Phone Control dialog box, click the LOCAL button in the Phone State
area to put the mobile terminal into Local Mode. (See Figure 9 on page 16.)
5. Open the Troubleshooting menu, point to RF, and click RF Main Mode.
The RF Main Mode dialog box appears.
Figure 12: RF Main Mode dialog box for Cell Mode
6. Select the following values on the RF Main Mode dialog box:
•Band = Cell (CDMA)
•Channel = 384
•Mode = Rx/Tx
7. Click Set.
Note: Be sure that the “RF Main Mode set successfully” message appears in the status bar.
8. Open the Troubleshooting menu, point to RF, and click CDMA Control.

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The CDMA Control dialog box appears.
Figure 13: CDMA Control dialog box for Cell Tx troubleshooting
9. Select the following values:
•State = Rho ON
•Band = Cell
•Radio Configuration = Mode 1: IS-95 Voice
Note: Do NOT select the Set default PDM values option
10. Click Execute.
11. Configure the spectrum analyzer using the following values:
• Center Frequency = 836.52 MHz
• Span = 100 MHz
• Amplitude = 20 dBm
• Attenuation = Auto
• BW = Auto
Table 2: RF PDM Values
Description/Field Reference Value
AGC2 -250
AGC3 -387
Pout at RF connector +20dBm
Current 500-600mA
Do NOT select
this option

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Figure 14: RF PDM Control dialog box for Cell band
12. Click Read Phone to update the values.
PCS Setup
Use the following procedures to prepare for PCS Tx troubleshooting using Phoenix.
1. Connect an RF test connector to a call box.
2. Connect the mobile terminal to the PC via a test jig. (The bottom connector is a
USB port.)
3. Connect a power supply to the mobile terminal.
4. Open the Troubleshooting menu, and point to Phone Control.
The Phone Control dialog box appears. (See Figure 9 on page 16.)
5. Click the LOCAL button in the Phone State area to put the mobile terminal into
Local Mode.
6. Open the Troubleshooting menu, point to RF, and click RF Main Mode.
The RF Main Mode dialog box appears. (See Figure 12 on page 18.)