Nokia NPD-4 Series Technical Documentation Manual page 14

NPD-4
Troubleshooting — RF
to center the VCTCXO frequency. The PCS transmitter is turned on and no TX baseband
modulation is provided. The carrier is then centered in frequency. This is done to the car-
rier after it has been mixed up to 1880 MHz, since it's easier to measure the tolerance of
1 ppm at 1880 MHz than it is at 19.2 MHz. Additionally the tone at 1880 MHz can be
measured without taking the phone apart.
The result is a PDM value for the AFC DAC, which must be within +/- 150, which corre-
sponds to 2.2 v on the VCTCXO control pin (pin 1) and the carrier centered within
+/- 100Hz. The VCTCXO must be able to be centered within a certain voltage range in
order to allow for aging of the crystal (the centering voltage slowly drifts over time and
the phone will eventually run out of voltage range if it begins too close to the edge of
the range).
Manual Verification: Using the RF Main Mode window in Phoenix, turn on the PCS trans-
mitter, and set it to channel 600. Do not add any modulation.
Using the RF Tuning window, set mode=RF Tuning and choose this tuning. Look for a
transmitted tone on the spectrum analyzer at 1880 MHz. If no tone is present, proceed
to Troubleshooting section.
Center the carrier to within +/- 100 Hz of 1880 MHz. (If sidetones are present, be careful
to center the carrier and not one of the sidetones, which will probably have a higher
amplitude than the carrier.) The values you enter in the "values" edit box are the AFC val-
ues which control the VCTCXO frequency. Start with a value of 0, then adjust until it is
centered, staying within the limits.
Troubleshooting:
1 If there is no tone, probe pin 3 of G501 for a tone at 19.2 MHz. If this is not
present check power supplies, particularly ensure 2.7v on VCTCXO Vcc pin, pin 4
of G501. Also check the control pin, pin 1 of G501, for a voltage between 0.4 and
2.7 v. If the voltages are correct, and soldering of all G501 terminals is correct,
replace G501. If 19.2 MHz tone is present but tone at 1880 MHz is not, trouble-
shoot PCS TX chain as described in the Probing Diagrams section.
2 If the carrier is present but the PDM needed to center it is outside of the +/- 150
range, or if it cannot be centered, there is a hardware problem.
3 In the following procedure, performing frequency centering on the RF carrier at
1880 MHz will detect frequency errors due to the VCTCXO and supporting hard-
ware, which will be the majority of the problems, but will not detect frequency
errors due to the hardware that mixes the VCTCXO tone at 19.2 MHz up to
1880 MHz. In order to troubleshoot this hardware also, frequency centering
should be performed on the 19.2 MHz tone to +/- 19.2 Hz on pin 3 of G501 using
a frequency counter, then the VHF and UHF LOs should be checked. Since this will
be time-consuming and will probably only account for a small percentage of the
failures, it is not recommended unless the situation justifies the time spent. The
VHF LO is inside the Robin IC (N601) and troubleshooting of the cell UHF LO is
Page 14
Nokia Corporation
CCS Technical Documentation
Confidential Issue 1 02/2003