If your processor board has been shipped to you as a bare board without the headers fitted, then first up we need to solder the Dual InLIne (DIL) headers onto the Arduino Mega 2560 module.
Use a fine tip on your soldering iron and not too high / excessive heat, together with some fine solder. I like to use something like a 0.5mm or 0.8mm solder in 60/40 tin and lead with rosin core. Tip here is to solder one corner pin of the header first, and then check that the header is straight and aligned on the board. If it has moved slightly and is crooked, now is the time to straighten it up. Once happy with the alignment I then solder the opposite corner pin, just to lock the header into place on the board. I then solder every second pin along the header and then come back down the opposite side, again soldering every second pin. This process spreads the heat out a little across the plastic of the header and the PCB and keeps it all a little cooler as you solder. Then proceed to solder up the other alternate pins until all done.
Note that you don't need to install headers into every section of the Arduino Mega module, as shown below. There are some pins that we don't require / use with the Weather Duino and there is no matching header socket on the receiver board. Once you have finished your soldering, check it under a magi-lamp for any solder bridges, shorts or dry joints. When happy clean up all the solder joints with some Isopropyl Alcohol and a clean tooth brush or similar to remove the dry rosin from the board.
If you had the test sketch loaded into your Arduino Mega (from above) you can now power up your processor and see that all is well and it is still functioning.
Use a fine tip on your soldering iron and not too high / excessive heat, together with some fine solder. I like to use something like a 0.5mm or 0.8mm solder in 60/40 tin and lead with rosin core. Tip here is to solder one corner pin of the header first, and then check that the header is straight and aligned on the board. If it has moved slightly and is crooked, now is the time to straighten it up. Once happy with the alignment I then solder the opposite corner pin, just to lock the header into place on the board. I then solder every second pin along the header and then come back down the opposite side, again soldering every second pin. This process spreads the heat out a little across the plastic of the header and the PCB and keeps it all a little cooler as you solder. Then proceed to solder up the other alternate pins until all done.
Note that you don't need to install headers into every section of the Arduino Mega module, as shown below. There are some pins that we don't require / use with the Weather Duino and there is no matching header socket on the receiver board. Once you have finished your soldering, check it under a magi-lamp for any solder bridges, shorts or dry joints. When happy clean up all the solder joints with some Isopropyl Alcohol and a clean tooth brush or similar to remove the dry rosin from the board.
If you had the test sketch loaded into your Arduino Mega (from above) you can now power up your processor and see that all is well and it is still functioning.