Nokia RH-57 Series Troubleshooting Manual page 45

Nokia Customer Care
Tuning Title
PA Gain Cell Po(0)-
Po(3)
Tx AGC
Issue 1 07/2004
Description
These tunings model the cell PA gain
curve by setting the PA AGC PDM to
several values and measuring output
power. First, the Tx PA AGC and the Tx
RF AGC are set to (approximately) their
maximum used values (not the maxi-
mum possible values, but the maximum
of the range over which they are used).
Then the Tx IF AGC is set so that the
transmit power on the antenna connec-
tor is approximately +11dBm (this power
is reported in the next tuning). Then, six
PDM values are written to the PA AGC
and the output power is measured for
each. These values are reported in this
tuning. The software then performs
curve fitting to interpolate between the
measured data points.
This tuning characterizes the AGC curve
by entering PDM values to the RF AGC
and measuring the output power.
©2004 Nokia Corporation
Troubleshooting - RF
Troubleshooting
5) If the carrier cannot be centered, check
to see if you can adjust to 2.2v on pin 1 of
G501. If you can, within the PDM range of
+/- 150, then the circuitry that delivers the
voltage is working correctly, and the
VCTCXO has a problem. Troubleshoot it as
described in the previous section. If you
cannot adjust to 2.2v within the accepted
range, then the AFC circuitry has a problem.
Troubleshoot it as described in the previous
section.
6) If there is a fault with both the AFC cir-
cuitry and the VCTCXO, then several combi-
nations of the previously described
conditions are possible. Start by ensuring
2.2v on pin 1 of G501 using a PDM within
the range +/- 150, then center the tone.
If the power readings are low, check the
AGC voltages. You can also probe on the PA
input to find out if the power level is low
going into the PA, or if the power level is
correct going into the PA but the PA gain is
too low. If the power level going into the PA
is too low, probe the Tx chain at all the
other points prior to the PA listed in the
table to see where the gain is lacking. When
that point is identified, check the soldering
of all related components, and replace com-
ponents until the fault is found. If the
power on the PA input is not low and the PA
AGC voltage is correct, similarly probe the
power at all points after the PA to find the
fault, being extremely careful not to short
the probing point to ground because this
will instantly destroy the PA. Visually check
soldering first, and probe on PA output as a
last resort.
Check Jedi (N601). Also check D400, which
generates the PDM signals. Check AGC PDM
voltages. Troubleshoot the rest of the cell
transmitter if needed.
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