Download Service Manual R250

Trouble Shooting Guide, Advanced
Fig. 11.3
Turn the modulation on.
Compare the inter modulation products with the one of a working phone.
They can not be too high.
If there is noise in the spectrum, the fault can be due to noise in one of the feed voltage, VRAD,
VVCO or VANA.
Noise can be due to e.g. ageing filter capacitors, usually the electrolytes, or deteriorated
performance in the voltage regulators of the radio.
If you have got a really good oscilloscope, it is possible to measure the noise, but usually it is
too hard. Noise in the spectrum can also come from the synths, either in the PLL-circuit N301,
N500 or in one of the VCO´s.
If the inter modulation products have-not got the right level, go to chapter ”Calibration IQ”fault.
If the static spectrum looks correct, the fault most certainly is due to the power amplifier.
Replace the power amplifier and perform a new radio calibration.
If the radio calibration succeeded, the fault was due to the power amplifier.
If the radio calibration failed, the fault can be due to noise in one of the feed voltage VRAD,
VVCO or VANA.
Noise can be due to e.g. ageing filter capacitors, usually the electrolytes, or deteriorated
performance in the voltage regulators of the radio.
4/00021-3/FEA 209 544/18 B
54(121)