Receiver Fault Finding; General; Agc-Block; Lna - Nokia NSB-7 Series Service Manual

PAMS Technical Documentation

Receiver Fault Finding

General

Middle channel 661 is used as a test channel 1960 MHz and signal level in RF generator
is set to –50 dBm. Signal levels and forms are referred in RF measurement points. Signal
levels can vary depending the measurement method. So it is recommended to make mea-
surements by your way and make own reference level table. The phone which you are
using for this reference table must be undamaged.
Hagar

AGC-block

AGC-block is inside HAGAR. AGC block can be tested measuring the IQ signal with the
oscilloscope. IQ signal in RF/BB interface can be measured at points RX1 and RX2.
Point RX1 is after AGC stage and from that point 5 gain steps (3 ... 8) should be found.
Basic form of signal can be seen in figure 4 in RF measurement points.
Point RX2 is before AGC stage and only LNA gain step (2... 3) is available in this point.
Basic form of the signal is illustrated in RF measurement points.
Controlling AGC with WinTesla
When continuous RX mode is used, AGC gain step can be selected by entering gain step
number into the AGC Absolute text box. When burst mode is used in RX AGC is automat-
ically adjusted by the system.
In burst mode signal level in point RX1 should keep its level when RF signal level is
adjusted in the limit of AGC dynamic range.

LNA

LNA operation can be checked out by measuring the signal level from points RX 11 using
spectrum analyzer. Signal level measured this point can be found in RF Testpoints. LNA
gain step can also be tested from point RX2 by oscilloscope.

RX-filters

RX-filters can be checked by measuring the signal level from points RX11 and RX13. Sig-
nal levels in these points can be found in RF Testpoints.
Mostly problem with these saw filter is the linearity over the frequency band. If that is
the case, the measurement should be carried out also with some edge channels.

Antenna Switch

Antenna switch operation can be tested by measuring the signal level from point RX13
with spectrum analyzer. Signal levels can be verified in RF Testpoints.
Antenna switch RX path is on all the time except during the TX burst.
Issue 1 06/00 ãNokia Mobile Phones Ltd.
Disassembly & Troubleshooting
NSB-7
Page 41