It is not uncommon to lose audio quality in a stereo system or for a video game console to stop working. More often than not, the reason stems from a blown Pico fuse. Electronic gear generates heat, causing circuits to work harder. Under too much strain, the circuit blows. This is why large computer operations are housed in cold rooms. Pico fuses are necessary to save the circuit boards from melting down.
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Things you need
- Needle-nose pliers
- Solder iron
- Rosin-core solder
Locate the Pico fuse. Remove the cover from the equipment and inspect the circuit board. Many circuit boards are designed to use a 12-volt, direct-current power supply. Often, a Pico fuse will be located near the supply. In other cases, such as an audio circuit, there may be a large power transistor which drives an output channel that is protected by a fuse. Find a 3/4-inch long, solid-colour fuse with wires at each end. It is slender and may have dark discolourations from the high heat that caused it to blow. It is soldered directly into the board.
Test the fuse with a voltmeter. If you are uncertain about the state of the fuse and there is no service manual to reference, it is best to test the fuse with a voltmeter. Locate the negative input to the circuit board. It will be indicated by a dash sign and the positive input will be indicated by a plus sign. Turn the power supply on and touch the negative probe to the negative input. Probe each side of the suspected Pico fuse. If it is blown, there will be power on only one side.
Remove the defective fuse. Turn off all power to the circuit board. Use a soldering iron to heat the Pico fuse attachment wires that are soldered to the circuit board. Pull gently with the needle-nose pliers as the connections are being heated. The fuse will pull out.
Solder in the new fuse. Trim the wire lead of the new fuse. Cut them to length with the pliers and bend the ends of the wires to fit the circuit board mounting holes. Heat the residual solder that puddled on the circuit board where one of the attach holes is located. When it melts, hold the fuse with the needle-nose pliers and press the wire leg into the hole. Do the same with the other hole. Add a small amount of new solder if needed.
Close up the case and test the repaired circuit.
Tips and warnings
- Some circuits use thermal circuit breakers and will reset when the circuit cools. The shutdown, in these cases, is only temporary.
- Do not confuse a Pico fuse with a resistor. Resistors have coloured bands. Pico fuses are both colour- coded for amperage rating and only produced in solid colours. Some circuits are very sensitive to overheating and can be damaged quickly. Other designers make their circuits robust to take abuse, such as electronics for children. Robust circuits stand a much better chance of being repaired by a simple fuse replacement. Do not touch the circuit board with bare hands when the circuit is powered. Only use the voltmeter probes.
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