Vctcxo Manual Tuning - Nokia 6255 Rf Description And Troubleshooting

6255/6255i/6256/6256i (RM-19)
RF Description and Troubleshooting
Test
Description
Point
7 If you do not see the VCTCXO signal at
test points 1-5, check the voltage at VR3
8 AFC voltage
N/A If an AFC voltage is missing, check the
UEM.

VCTCXO Manual Tuning

The VCTCXO can be manually tuned to verify when a mobile terminal is tuned incorrectly
or if mobile terminal cannot make a call. Monitor the RF signal at the mobile terminal's
output.
1. 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 for an
example of the Phone Control dialog box.)
2. Click the Execute button.
3. On the AMPS Control dialog box, set the Set Channel field to 384, the Power
Level field to 5, and select the Transmitter ON check box. (See Figure 10 on
page 16 for an example of the AMPS Control dialog box.)
4. Click the Rx RFI tab, make sure the AFC Control check box is cleared, and click
Execute.
5. The frequency accuracy of the VCTCXO can be measured using an HP8960 callbox
in AMPS mode or a spectrum analyzer at the output of the transmit chain.
• If using a spectrum analyzer, set the center frequency to 836.52MHz and the
span to 2MHz initially. Establish a marker at 836.52Mhz.
• If using an HP8960, set the callbox System Type to AMPS, and set the ACC
channel to 384. Use the Frequency Stability measurement to center the
VCTCXO (minimum Frequency Error).
6. Use the RF PDM component to adjust the AFC to center the VCTCXO. The tuning
range is approximately +/-10kHz.
7. Adjust the AFC so that the output signal is within +/-150MHz. If using a
spectrum analyzer, narrow the span to 1kHz or less.
8. Replace the UEM if the VCTCXO does not tune correctly.
Page 54
Table 15: VCTCXO Test Point Output Values (Continued)
©2005 Nokia Corporation
Nokia Customer Care
Value
2.8V
1 to 3 Volts (adjustable with the AFC slider
on the RF PDM Control in Phoenix)
1.2V for PDM 0
0V for PDM -1024
2.4V for PDM 1024
Company Confidential Issue 2 05/2005