Synthesizer Troubleshooting; Vctxco Troubleshooting - Nokia 2366i Rf Description And Troubleshooting

2366i (RM-155)
RF Description and Troubleshooting

Synthesizer Troubleshooting

Faulty synthesizers can cause both Rx and Tx failures during tuning, in addition to the
VCTCXO tuning. However, first check for the presence of various LO signals and their
proper levels. If everything fails, it may be necessary to check the reference clock
(19.2MHz) which is needed for the mobile terminal to power up. The 19.2MHz signal is
also important because the N7100 Receiver IC is sensitive enough to pick up a very weak
19.2MHz clock, resulting in intermittent problems such as a constant mobile terminal
reset.
The Synthesizer has the following characteristics:
• TX Local Oscillator (LO): 1099.6–1131.08 MHz for the CELL band, and 1233.333–
1273.333 MHz for the PCS band, with the offset phase-locked loop (PLL) inside
the TX IC N7001.
• LO frequency calculation:
• CELL: LO = TXfreq x (4/3)
• PCS: LO = TXfreq x (2.3)
If the PLL frequencies are incorrect, the following causes are possible:
• Power supplies to the PLL portion
• Control line to voltage-controlled oscillator (VCO).
• Loop filter or resonator components are missing or incorrectly installed.
• 19.2 MHz reference clock signal is missing or low.

VCTXCO Troubleshooting

The VCTXO operates on 19.2 MHz and provides the reference signal for the synthesizer. If
the 19.2 signal fails, the mobile terminal does not power up.
Use the following procedure to troubleshoot the VCTXO:
1. Check for the presence of the signal at the following points (see figure x):
a. RF_CLK_IN, clock reference to the TX RF IC should be ~ 8 dBm.
b. RF_CLK_UPP, clock reference for the UPP IC, should be ~ 3 dBm.
2. If the VCTXO signal is not present at any of these points, check the voltage at
VR3 (R7119), the main supply line for the VCTXO. The signal should be 2.7 V dc.
See figure x.
3. Check the AFT voltage. The signal should be between 0 and 2.5 V dc, and should
be adjustable by operating the AFC slider on the RF PDM control window in
Phoenix (see figure y).
4. If the AFC voltage is not present, check the UEMCR IC.
5. If the frequencies coming from the phase locked loop (PLL) are incorrect, the
following possible causes exist:
Page 36 Company Confidential Issue 2 - February 2007