Principle electronic components for maintenance part 2:
We'll resume in this article the basic electronic components needed in the process of repairing the laptop motherboard, we'll see in this article two components: the fuse and the diode, we'll discuss their functions and their failures and how to test them.
The fuse:
The fuse is a safety component, it protects the circuit from overcurrent, it's made of a material that melts when too much current flows through it thereby making an open circuit and stopping the current from flowing to the circuit and damages other components.
Circuit symbol:
The symbol below is used to represent a fuse in a schematic:
The letter F is used to represent a fuse.
The fuse failure:
The fuse has only one failure: shorted or cut, it acts like an open circuit and preventing the current from flowing.
How to test a fuse?
You can test the fuse using the multimeter set as ohmmeter or the simplest way set in continuity test mode.
1- Testing with continuity test mode:
Set the multimeter to continuity test mode then put each probe in one terminal of the fuse, it doesn't matter the position, it you can hear a beep that means the fuse is ok, if you don't hear a beep the fuse is shorted or cut.
2- Testing with resistance mode:
You can use the resistance mode to test a fuse if your multimeter doesn't have a continuity test mode.
Set the multimeter to resistance mode, and choose the lowest range.
- Connect the probes to the fuse and press gently.
- If the fuse is ok you should read a very low resistance, and if you read 1 or OL it means the fuse is shorted or cut.
Diode :
A diode is a two terminal electronic component used control the current flow by blocking it in one direction (the reverse direction) and allow it in the other one (called the diode's forward direction).
Circuit Symbol :
A diode has two terminals that are polarized, the positive terminal is called the anode and the negative one is called the cathode, current can only flow from the anode to the cathode (from + to -), the circuit symbol of a diode is:
And the letter used for diodes in circuits is D.
Characteristics of a diode:
There are some points to take into consideration when working with a diode:
- The diode doesn’t let the current flow in the forward direction until the voltage reaches 0.3 V for germanium diodes and 0.7 V for silicon diodes, this voltage is called the Forward bias Voltage and it is consumed by the diode, meaning the voltage will drop by the Forward bias voltage, example: if the voltage from a battery is 3V, it will be 2.7V after a germanium diode and 2.3V after silicon diode.
- The diode blocks the current until a certain voltage called The breakdown Voltage, after that the current will flow in the reverse direction.
Light-Emitting Diodes (LED) :
A LED is a special diode that emits light when conducting current, it has the same characteristics like the normal diode, it allows the current to flow in one direction and blocks it in the other one, it has a forward bias voltage which is greater than the forward bias voltage of normal diode (from 1.2V to 3V depending on the light color that emits).
Diodes Failure:
Diodes have two types of failures: short-circuited or open-circuited (cut).
When the diode is short-circuited it acts like a wire allowing the current to flow in both directions, and when it is open-circuited or cut it acts like and open circuit and not allowing the current to flow in both directions.
