Table of Contents
Advertisement
TxVCO
Ch 94
CH 30
Oxfam
Ch 570
CH 826
5.2
How to find the fault
The TxVCO calibration is the sixth step in the Radio calibration.
If the first fault showing up is "GSM Static TX Check Amplitude", go to chapter "Static TX-
fault.
If the first fault showing up is "Calibration off IQ Filter LPBW", go to chapter "Calibration IQ"-
fault.
This chapter only deals with faults where "GSM Calibration TXVCO ch 94 or 30 GSM900 and
ch 570 or 826 GSM1800" is the first fault showing up at the Radio calibration.
Open the phone and check for liquid damages.
No further action should be taken for a liquid damaged telephone.
Measure the resistance of N401 pin 14 against ground >10 Kohms.
If the resistance is much lower, usually around ~200 ohms, the power amplifier N401 is faulty.
Give the board power and start the board.
Measure the voltage at C853 +1.2 V
Start the phone in the test program.
GSM 900:
Start the transmitter in static mode at channel 62 902.4 MHz and check the amplitude and the
frequency.
If the frequency is misplaced, try to lower the "Adjust sweep current" until the frequency of the
transmitter has locked on.
We propose the following settings on the spectrum analyser while measuring:
CF- 902.4 MHz, SPAN- 200 MHz, RBW- 10 kHz, VBW- 10 kHz and Sweep- 30 ms.
If the transmitter locks on, start the transmitter in switch mode at channel 62 with DAC 7 value
at "FF".
4/00021-3/FEA 209 544/18 B
Min.
Max.
85
BB
133
187
5D
78
93
120
Min.
Max.
55
87
85
135
AA
D2
170
210
Table.5.1
. Replace the capacitor if the voltage is lower.
DC
Trouble Shooting Guide, Advanced
Hex
Dec.
Hex
Dec.
Hex
Dec.
Hex
Dec.
23(121)
Advertisement
Table of Contents
