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Trouble Shooting Guide, Advanced
The power calibration is a part of the radio calibration in EFRA
The calibration is performed in 15 steps for GSM 900, from the highest 5, to the lowest 19.
And in 16 steps for GSM 1800, from the highest 0, to the lowest 15.
A computer control the calibration by setting the Power level DAC for the phone at the current
power level and checking the output power using a spectrum analyser or a GSM test set.
Default values are used as starting DAC values.
The computer changes the DAC value to attain the correct output power for the current power
level.
The value is temporarily saved in the RAM of the phone.
When the computer has attained the right output power for each power level, the values for the
power levels not in use are first interpolated then are all DAC values saved in the EEPROM.
If the correct power is not achieved or one of the DAC values is outside of the limits, then the
calibration has failed and nothing is written in the EEPROM.
8.2
How to find the fault
If the power calibration failed or if the output power is several dBm too low, open the phone and
check for liquid damages
No further action should be taken for a liquid damaged telephone.
Make sure the antenna connection (X101) is correct.
Give the board power and start it in the test program.
Measure the voltage at C853 +1.2 V
.
DC
If it is lower, replace the capacitor.
For GSM 900:
Start the transmitter in switch mode at channel 62 and DAC 7 value at "FF".
Check if there is enough output power, 30- 35 dBm at the antenna plate using the spectrum
analyser.
We propose the following settings while measuring:
CF- 902.4MHz, SPAN- 0 Hz, RBW- 300 kHz, VBW- 100 kHz and Sweep- 0.8 ms.
If the output power is correct, the fault can be due to the frame.
The fault can also be due to a change, because of ageing, in the characteristic in some of the
components participating in the power regulation.
For some power levels can this make the output power or the DAC values ending up outside the
limits.
In that case, the fault usually is due to N401 or N450.
The fault can also be due to N800, N570 or D600.
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