Ericsson A2618s - Page 27

Trouble Shooting Guide, Advanced
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 Ericsson Mobile Communications AB
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7.3.2 The output power is too high
When the output power is too high (usually a few dBm over the limit), it usually is due to a
change in characteristic, because of ageing, in some of the components in the power
regulation.
The same thing happens when you replace e.g. N400.
The only thing necessary to do is a new power calibration (a part of the Radio calibration in
EFRA).
7.3.3 The output power is too low
For EGSM900:
Start the transmitter in switch mode at middle channel (37) with ”DAC 4 value” at FF.
Check if there is enough output power (31 – 35 dBm) at the antenna connector, use the
spectrum analyser.
We have been using the following settings on the spectrum analyser while measuring:
CF- 897.400 MHz, SPAN- 0 Hz, RBW- 300 kHz, VBW- 100 kHz and Sweep- 0.8 ms.
If the output power is correct, the fault was either the back cover or the antenna connection.
Measure the PAREG at R497, 2,9 Vp-p/216 Hz, Fig. 7.4.
If the voltage is too low, the fault can be due to a short circuit in C510,
but usually it depends on N400, N500, N700 or D600.
Fig. 7.4
If PAREG is correct, measure the signal TXLB on N390:4 (13 dBm) and on D401:2 (~8
dBm).
If both the signals are correct and there is no or low output power, check the VCTLLB
voltage to N200: 6, 3.7 V p-p/ 216 Hz.
If the voltage is correct, replace N400.
(It is not possible to measure the signal out from N400).
If the fault remains it can be due to C405, C406, C408, or N200.
If only the signal at D401 is missing the fault is due to D401 or N400.