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

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

Nokia Customer Care RF Description and Troubleshooting
6255/6255i/6256/6256i (RM-19)
Issue 2 05/2005 ©2005 Nokia Corporation Company Confidential Page 3
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

6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting Nokia Customer Care
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Nokia Customer Care RF Description and Troubleshooting
6255/6255i/6256/6256i (RM-19)
Issue 2 05/2005 ©2005 Nokia Corporation Company Confidential Page 5
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.

6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting Nokia Customer Care
Page 6 ©2005 Nokia Corporation Company Confidential Issue 2 05/2005
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

Nokia Customer Care RF Description and Troubleshooting
6255/6255i/6256/6256i (RM-19)
Issue 2 05/2005 ©2005 Nokia Corporation Company Confidential Page 7
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

6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting Nokia Customer Care
Page 8 ©2005 Nokia Corporation Company Confidential Issue 2 05/2005
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

Nokia Customer Care RF Description and Troubleshooting
6255/6255i/6256/6256i (RM-19)
Issue 2 05/2005 ©2005 Nokia Corporation Company Confidential Page 9
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

6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting Nokia Customer Care
Page 10 ©2005 Nokia Corporation Company Confidential Issue 2 05/2005
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.)