Some Knowledge

Electronic gear all works on the same basic principles.  There will be a power supply to supply electrical energy to the device.  In most electronic gear, the power supply will take AC from a wall outlet, transform it to a lower voltage, then rectify and regulate it at some DC voltage.  When looking for problems with an electronic device, it is best to start with the power supply.

You will need a volt-ohm meter.  Check the fuse for continuity.  If the fuse is blown, check the transformer for a short circuit.  If the transformer checks out good, try replacing the fuse.  If it blows immediately there is some problem with too much current flowing somewhere in the circuit.

Identify the main power-using components.  This may be an output amplifier.  If it looks burned, it is probably fried.  If there is a crater in the package, the unit has failed explosively.  Your sense of smell can come in handy for finding things like burned resistors or popped capacitors.  Often, there will be a burned trace on the circuit board where too much current has melted the copper.

After looking around for obvious problems, it is time to check the power supply line for short circuits.  If an obvious short exists, you will have to do some work on the board.  This involves removing components with a soldering iron, de-soldering wick, or a de-soldering tool commonly called a solder-sucker.  Remove one device at a time, starting with the most power-hungry devices, because these will be the most likely to blow due to excess power consumption.  Check the circuit for shorts again after removing each device.

If you start with the output circuits and remove the devices in sequence, you will most likely find the bad circuit quickly.  Once you find the bad device, get a replacement and solder it in place.  Replace all the devices you removed and check the circuit again for shorts.  If it checks out good, replace the fuse and fire up the device.  Check that the voltage on the power rail is correct.  Check the device for proper operation.  Then, put the equipment back together.  The time you spend removing circuit boards and putting them back in the equipment will account for most of the time you spend troubleshooting and repairing electronics.

It only takes one shorted transistor or IC to break an electronic device.  If you are not lucky enough to be working on something that has had a catastrophic failure, you will need more sophisticated equipment to discover the problems.  I am talking about an oscilloscope here.  You will also need a circuit diagram if the device is not simplistic and laid out well.  You will need to trace the signal through the device with the scope and find out which circuit is causing distortion or signal loss.  This takes time.  You will eventually identify a bad device which can be replaced with the proper replacement.   You have to know what you are doing.

Electronic equipment all operates pretty much the same, in principle.  Once you know how a circuit is supposed to work, you can trace it for flaws and repair it.  It takes some basic test equipment and some knowledge of the device you are working on.  Information on how semiconductor devices operate is important to have.  Often, the problem will be nothing more complicated than a blown voltage regulator in the power supply.  Such faults are easy to identify by tracing the circuit with a volt meter.  If you want to learn electronic repair, get some old equipment, take it apart, and use a volt meter and oscilloscope to look at the circuitry.  Get some practice on tracing circuitry that works, and when you have something that’s broken, you will be able to figure out where it has failed.

As in any circumstance, exercise extreme caution in working on electrical devices.  Televisions contain possible lethal voltages.  Old tube-type circuits all have a high voltage plate supply that can kill.  Use insulated tools and do not put your fingers on any part of the metal circuitry.  Sometimes a malfunctioning device will heat up and can cause burns if touched.  Be careful that you do not come into contact with the mains of the power supply.  Safety is important.