Electronics Repair - The Fuse

Let's face it, most people aren't skilled at electronics repair.  But that doesn't stop people from trying.  After all, if your TV stops working, it's out of warranty, and paying a repairman would cost almost as much as buying a new TV, why not try and repair it yourself?  What do you have to lose?

Back before I learned how to diagnose and repair broken electronics, I would always hope the problem was as simple as a burned out fuse.  Suppose you take apart that TV or other electronic item and you do indeed find a burned out fuse.  Simple fix right, you just replace the fuse?  Wrong!  Nine times out of ten, if you replace the fuse and turn it on it will burn out the new fuse.

The job of a fuse is simple, to protect against too much current.  Let me be clear, the fuse does nothing to protect against over voltage (such as a power spike).  The thing to understand about current, you cannot force current through a device, instead the device itself restricts how much current flows through it.  So if a fuse burns out this means one of several possibilities.

1. The fuse was defective or weaken from age causing it to fail below its rated limit.  In this case replacing the fuse with a new fuse will repair the item.
2. The electronic device was poorly designed, as a result it pulled slightly more current than the fuse was rated for.  In this case, replacing the fuse with a slightly higher rated fuse will repair the item.
3. The electronic device has other faulty components which created an electrical short.  This short is what caused it to pull more current and burn out the fuse in the first place.  In this case if you replace the fuse, when you turn it on again it will just burn out the new fuse.

Again I want to be clear, #1 and #2 are rare, usually the problem is #3.  So if you find a broken fuse, you need to check the rest of the system for shorted or damaged components.  Failure to do so will just waste your time and money.

They put fuses into electronics because electronics fail.  If it fails with a short and there is no fuse, the device will pull more and more current, getting hotter and hotter.  Eventually the device could burn up or even explode.  So when it comes down to it, the whole reason for fuses is to prevent fires and explosions when electronics fail.