For an upcoming Bluetooth speaker project I needed a heat gun to mold some PVC pipe. In a local second hand store I found one which would be ideal, only thing was it didn't work!! No problem, let's fix it!
SAFETY FIRST! Always unplug electrical equipment from the mains before working on it! Do not rely on just switching the socket off, physically unplug it. When testing use an RCD (residual current device) which will trip out in the event of a malfunction. Take care!
In the video I show my troubleshooting approach and how to check the various components.
Step 1: Taking It Apart
There was no life at all when I plugged the heat gun into the power. I checked the fuse and that was OK. The next step was to get inside to check the continuity of the cable. Remove all the screws and slide the front part off.
Step 2: Continuity Test
Once inside I could check the cable continuity with a multimeter. Both leads were OK so the problem lay deeper..........
Step 3: Further Investigation
There is quite a sophisticated control circuit inside and upon examination I noticed a resistor that was burned out.
I measured it's resistance and it was 0.6 Meg ohms but the colour code read 47 ohms, clearly something wrong!
Before removing the circuit board from the heat gun draw a diagram of where all the wires go so you can put it back together correctly! Take some photos too in case you forget something.
Step 4: Are Other Components Damaged?
There was a possibility that other components had been damaged by the resistor failure. I could check most of the other diodes and transistors in circuit but the triac that controls the heater element needed to be removed from the circuit. Fortunately it tested OK.
Step 5: Finding a Replacement Resistor
To replace the burned out resistor I looked through my "packrat" hoard and found an old PC power supply with a 50 ohm resistor of the correct wattage. Checked it with a multimeter and soldered it in place. Now to test it!
Step 6: Put It Back Together and Test!
I reassembled the heat gun using the diagram I had made to ensure the wires all went back in the right place. When testing use an RCD (residual current device) for your own safety!
Step 7: It Works!
After reassembly I do a final check. The heat gun has two switch positions. The first has a fixed temperature of 50 degrees Celsius and you can adjust the fan speed. In the second position the temperature can be set from 50 to 650 degrees Celsius in 10 degree steps, all works perfectly!
I was very pleased to be able to restore to life this heat gun. It only cost me 5 Euros and the replacement resistor was free, a win - win!!