Icom IC-740
Usage of TDA2003
If you turn AF gain fully CCW you can still hear some white noise, mainly when you use headphones. This white noise is masked by the noise coming from IF stages during a normal reception. However, it is still there and can make digging of the weakest signals more difficult.
I replaced the original AF power amplifier uPC1181H by the modern TDA2003.
It is a rather brutal modification. It is not just adding one or two parts at the bottom of the PCB. On the other hand TDA2003 has less outlets and requires about the same number of external parts. Thanks to this no drilling was necessary, and no existing path on the PCB had to be cut. The modification uses existing PCB patterns and holes plus a few parts had to be soldered at the bottom of the PCB.
The difference in level of the white noise generated by uPC1181H and TDA2003 is really significant. I realized this again recently when, for some diagnostics reasons, I replaced momentarily the MAIN board with an unmodified one.
TDA2003 replaces the IC10 in the
original schematics of the MAIN board, see:
Schematics
diagram
TDA2003 is mounted horizontally to fit the given space on the heat-sink.
Pin assignment of TDA2003 on the
MAIN board. Two holes will remain free:
