Mobile phones have become an integral part of our daily lives; in fact, it is difficult to function in the twenty-first century without one. If you have a mobile phone or are a DIY or technician, it is important for you to understand shorts and short circuits, which I will describe in this post.
short definition
What are the possible causes of short circuits?
- Water damage is the most common cause of a short circuit.
- Overheat.
- Components that are damaged.
- Circuit board debris
- Drop.
Water harm
When water molecules are present on a circuit board, this occurs. In one of my earlier posts, I discussed how water can be so destructive to a mobile phone. Water infiltration will never leave your circuit board in the same condition it was found in. Shorts are a major issue caused by water.
Water is an excellent conductor of electricity, and it transports electric charges from one voltage line to another, resulting in... you guessed it, a short. Water can also induce oxidation, which is the most severe type of short. As a result, anytime without removing the battery or turning off the phone altogether, would lessen the effects of water.
Overheat
Playing heavy games on your mobile phone will lead to overheating, heavy browsing will lead to overheating, watching movies during the day when the sun is hot will lead to overheating, and keeping your phone in an externally hot environment will lead to overheating.
Internal overheating occurs when circuit components are worked up and stressed. Circuit components are semi-conductors and are metallic in nature, therefore during the process of overheating, they expand. Metals generally expand whenever they're heated up, and when they cool they contract. Constant expansion and contraction lead to so many things and one of them is short, in the sense that over-expansion can make Integrated Circuits (IC) balls to misalign, and sometimes they lead to poorly soldered joints. When an IC gets damaged, the entire voltage line to which it is connected could get short. I can recall an experience where I was delivered a bad battery for a client's music box, and on inserting the new battery, the main power IC got overheated immediately. Despite the fact that the battery was removed instantly, the entire vbat line was short to ground. I was able to track down the short and resolve it, then I ordered for another battery and finally everything works fine.
Damaged components
A damaged circuit component also can lead to a short circuit. A circuit component can get damaged due to old age, oxidation, over-voltage, and over-heat.
List of circuit components that get short the most
- Capacitors.
- Integrated circuits (IC).
- Diodes.
These components easily become short, and when they do, the device will show the effects of short.
Debris on Circuit board
Debris also means unwanted particles or dirt. Some debris have metallic properties and conduct very small amount of charges from one track to another, therefore causing short.
Drop
This is the last cause of short. While drops are known to cause disconnection of ICs, some lead to short in other cases.
Effects of short on a circuit board
Below are the effects of short on different circuit boards:
- Dead phone.
- Severe and constant heating even when the mobile phone is not operated.
- Quick battery discharge.
- The mobile phone may be turning off the charger's LED indicator.
- The mobile phone may be charging without plugging in any charger.
- No backlight.
- A completely non-functional part.
How to Detect and Confirm a Circuit Board Short
A multimeter can be used to confirm the presence of a short on a circuit board that shows any of the following consequences of a short. Schematic designs might be necessary in certain difficult scenarios.
To confirm a short, a multimeter is set to continuity mode, also known as buzzer or diode mode, and voltage lines on a circuit board are read. A multimeter has two probes, one for positive and one for negative readings. For brief confirmation, the red probe is placed on the ground (which includes any random metallic part attached or soldered to the board but does not carry voltage) and the black probe is placed on power. The probe is used to test critical voltage lines such as vbat, bus, CPU tracks, and power IC.
When the red probe of your multimeter is placed on ground and the black probe is placed on the vbat line, a red light will illuminate or a beep sound will be heard, indicating that the vbat line is confirmed to be short. Similarly, if you take a reading of both sides of any capacitor with the black probe on one of the two sides and the red probe on ground, and you hear a beep sound when you read both sides, the capacitor is short or the voltage line along
By putting the multimeter's two probes on the two sides of the object, you may advance your confirmation test.
How to track short on a circuit board.
You can quickly track a short on a circuit board using any of these five methods:
- Visual inspection.
- Multimeter.
- Use freeze spray or paste.
- Voltage injection.
- Thermal camera.
Visual inspection
Many of times when circuit components get short like capacitors or ICs, they burn out and deter from their normal shape and look. A quick visual inspection can quickly point out the faulty component. A capacitor may either appear bulged out or darker than others or partially melted, an IC can show signs of burns on one corner, a diode would leave its inner metallic part intact but the outer covering would be burnt or powdery. Removing and replacing these damaged components would solve the short circuit.
A capacitor is not compulsorily replaced because a circuit board can still perform core functions without them.
Multimeter
You can track short with the use of a multimeter. A capacitor or diode that beeps when you take the reading of both sides is short, replace the diode with an exact replacement, and you can just simply remove the capacitor. Pls make sure your multimeter is in appropriate functioning state to avoid misleads.
When an entire voltage line is short, this could be a bit tricky because several capacitors would show signs of short and would you start removing all of them? Definitely no! The short arise from only one of the capacitors or the IC to which they're connected, how do you find out the exact one that leads to the voltage line short? Read below.
Use of freeze spray or paste.
When an entire voltage line is short, several capacitors on that line would display short, and the respective IC would also display short, however, the short circuit is only caused by one of the components.
How do you get that exact component?
You can get the exact component by applying freeze spray or thickened flux paste onto the section that all displays short. Freeze spray gives the fastest and most accurate result than paste which may take more time before you get changes, if you're not sharp enough you may not be able to use paste effectively. You can get freeze spray at an affordable price in any repair part sales store in the market or you can just order for one online.
After applying freeze spray, you inject voltage via battery or a DC power supply, the exact short component melts the freeze spray fastest, and in so many cases that I've encountered, it is always a capacitor. Smiles. Capacitors are always the culprit!! This does not mean you should be limited to capacitors only, a short IC could also be the result and it happens often too.
Voltage injection
This is a very common step used to track a short. High voltage is injected into a circuit board at any positive terminal. Any short component would quickly react by giving a pop sound or get quick burns and I've seen some that just heat up and throw themselves off the circuit board. Those are old boards actually. In a normal case, a shorted component would get severely hot than the other components. This is the component that needs to be replaced.
Some people perform this step with the use of a short killer since this is the primary function of a short killer, however, short killers have been proven to be ineffective so many times, injecting very heavy voltage kills some circuit boards or causes damage to other innocent components. If you're having the thought of getting a short killer quickly erase that thought off your mind unless you are someone who likes doing extra work that could have been avoided.
Thermal camera
This is the most advanced way to track the cause of a short circuit on a board. Genuine Thermal cameras are pretty expensive in the sales market but they're really worth the try.
Thermal cameras detect quick temperature change in semi conductors and circuit components when voltage is passed along the board. The component marked as the culprit should be diagnosed, it's tracks also, and the short should be confirmed with the use of a multimeter. Check the video below for how to professionally use a thermal camera.
Solution to shorts on a circuit board
- Brush out every board that has signs of corrosion or debris using IPA and a heat gun.
- Apply flux paste on the circuit board and reheat the board. This removes any water molecule or debris that hid under circuit components and could not be affected during brushing.
- Remove only faulty capacitors, replace any diode that shows sign of a short.
- Remove and replace IC that shows sign of short.
Even though solving shorts might be a difficult chore at times, it is fairly simple if you take the proper procedures and go slowly. Diodes are a less frequent source of shorts than capacitors and integrated circuits. By this point, I think you are fully aware of shorts and how to address any short circuits that may arise. Please let us know in the comment box if any aspect of this post is still unclear to you.