Intro: Long Range FM Transmitter ,Part 2 Assembly Tips
This is how the finished one looks like
Step 1: The Plain PCB
This is how the bare PCB looks like
Step 2: Using the Heat Sink for the Power Transistor
The power transistor (1st image) needs a heat sink (2nd image) compulsorily. It has as usual 3 legs . The notch is the emitter and must watch it properly.The black heatsink has a cut portion.Force a screw driver (image 3rd) in the cut area to make it little wider.Then push the transistor maintaining the notch in line with the cut area that will go smoothly into the heat sink. Then remove the screw driver .The job is done (image 4th).
Step 3: Preparing the Coil for Soldering
These are super enamelled coated wire used in motor winding.Use a sharp knife to remove the coating at the end points such that copper is clearly visible in all sides.
Step 4: Making the Holes Little Bigger on PCB
Some Components like trimmers (image 1) and the coils may not fit on the respective holes on PCB easily. So use some pointed tool to make the holes little bigger (image 2) and then it looks like this (image 3)
Step 5: Start Soldering
First insert all the resistors and bend their legs. Must use a 25 watt soldering iron and then do the soldering that requires some little skill. The next component to be inserted are ceramic capacitors. But take care not to apply soldering iron to 2 points of the same capacitor one after another. First solder any one point and then go over to some other and then come back the first one after some time as it would have cooled by that time. Follow the same procedure for transistor legs. Never solder the 3 points of a transistor one after another in sequence. It may damage the transistor.Final soldering side shall look like the 2nd image. Any dry or bad soldering will affect performance.While inserting the power transistor make sure it does not get flushed to the board but maintain a little gap as seen inImage 3 but not like this as seen on image 4
Step 6: Using a DC Socket
Using Febi Quick fix a DC socket as shown. Solder with wires for DC +ve and -Ve
Step 7: The Final Assembled PCB
It looks like this
Step 8: Some More Tips
1. It is advisable to engage any electronics technician for soldering if one has no prior professional experience in soldering and component identifying. Any excess heating more than 2 seconds may damage the component. Use only 25 watt soldering iron. Placing right value of resistor is most important. Read the colors carefully to ascertain its value. If a multimeter is available , then better measure it in ohms / Kohms range. It may not give exact value. Plus or minus 10% is acceptable. Reading disk ceramic capacitors need expertise. Place them correctly. Please refer the image.
2. Some components might have accumulated dirt on their legs by oxidation due to storage. Must clean them thoroughly to remove the dirt with a knife all around before soldering. The metal transistor as an example as seen in the packet. Better clean all the component legs even if they have no dirt on them.
3. If the trimmer pins are not going inside the holes try to slightly make the holes on the PCB bigger by some sharp pointed pin.
4. Mount the black heat sink on the metal transistor before mounting on the PCB.
5. Solder cut pcs of resistor legs to the microphone and solder them on to the PCB by proper polarity. The body is –ve.
6. Maintain the legs of transistors at least 5mm above the PCB and all resistor legs & coils on sleeping position as close to the PCB. Capacitors as usual standing but solder the legs as short as possible to the board.
7. The coils are super enameled coated. Don’t be under the impression that they are copper. Must clean their ends only thoroughly to remove the enamel with a knife before soldering.
8. Must take a tapping from coil no 1, after 1 turn by scratching with a knife the enamel at a point and then use any cut piece copper wire of resistor (not iron wire) to solder there and connect the wire end to the hole on the PCB .
9. L3 and L4 must be at 90 degrees to each other.
10. Cleaning the dirt and rust on the legs as explained are very very important. All technicians know it. A beginner must understand this. Otherwise those components will never catch solder.
11. May use 9 volt battery by soldering the red to +ve and black to –ve. For using on 12 volt the DC socket has 3 pins. The center pin is 12v + and other 2 pins are for 12 volt –ve. Connect the same accordingly with small pcs of wire. Red + ,Black –ve to the DC socket.