TABLE OF CONTENTS
- Introduction.
- Definition of short.
- What are the causes of short circuits.
- Water Damage
- Overheating
- Damaged Components
- Debris on Circuit Board
- Drop
- Effects of short on a circuit board.
- How to detect and confirm short on a circuit board.
- How to track short on a circuit board.
- Solution to shorts on a circuit board.
Introduction
Mobile phones have become part of our everyday life, in fact it is hard to do without a mobile phone in this 21st century. If you have got a mobile phone or you are a DIY or technician, it is a good thing for you to have full knowledge about shorts and short circuits which I am going to be explaining in this article.
Definition of short
When I say short, a circuit board is short, or you have a short circuit board, what do I mean by that? A short circuit in simple terms is a circuit where electric current is passing through where it is not supposed to pass. A short is when two different tracks come in contact with each other thereby cutting out normal current flow on a circuit board. It can also be likened to mean two or more voltage lines which are not meant to be in contact with each other, are actually bridging, leading to a short circuit. I believe you're now getting what I mean by a short circuit. So let's move on.
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| Photo credit_Pexels |
What are the causes of short circuits
- The first and most popular cause of short circuit is water damage.
- Overheat.
- Damaged components.
- Debris on Circuit board.
- Drop.
Water damage
This happens when water molecules is present on a circuit board. I explained in one of my previous articles how water can be so damaging to a mobile phone. Water intrusion will never leave your circuit board the same way as it was. One big problem water causes is shorts.
Water is a good conductor of electricity and it conveys electric charges from a particular voltage line onto another voltage line leading to... yeah you got that right, a short. Water also cause oxidation which is the worse form of a short. That is why whenever any electric device drops in water I always advise that you try to cut out the electric current in the phone by either taking out the battery or completely switching off the mobile phone. This would reduce the damages exerted by water.
Overheat
Playing heavy games on your mobile phone will lead to overheat, heavy browsing will lead to overheat, watching movies during the day when the sun is hot will lead to overheat, keeping your phone in an externally hot environment will lead to overheat.
Internal overheat 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 a 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 get 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 that 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, 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 board:
- Dead phone.
- Severe and constant heating even when mobile phone is not operated.
- Quick battery discharge.
- The mobile phone may be turning off charger's LED indicator.
- The mobile phone may be charging without plugging in any charger.
- No backlight.
- A completely non-functional part.
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| Short circuit iphone |
How to detect and confirm short on a circuit board
On a circuit board that displays any of the above effects of short, you can check to confirm the short on the circuit board with the use of a multimeter. In some complex cases schematic diagrams would be required.
To confirm short, a multimeter is set to continuity mode also known as buzzer or diode mode, and then used to read voltage lines on a circuit board. A multimeter has two probes, the red probe for positive and the black probe for negative. For short confirmation the red probe is placed on ground (ground includes any random metallic element that is connected or soldered to the board but does not carry voltage) and the black probe is used to check important voltage lines like vbat, vbus, CPU tracks, power IC.
If your multimeter turns on red light or makes a beep sound when you place the red probe on ground and black probe on vbat, then the vbat line is confirmed short, also when you take the reading of both sides of any capacitor with the black probe on any of the two sides and red probe on ground, and you get a beep sound when you read the both sides, then the capacitor is short or the voltage line along which the capacitor works is short; only one side of every capacitor should give a beep sound with respect to ground.
You can take your confirmation test to the next level by placing the two probes of the multimeter on the two sides of every circuit components. A capacitor should not give a beep sound, a diode should not give a beep sound, a coil should give a beep sound, if a coil doesn't give a beep sound then the coil is open, some resistors should also give a beep sound like resistors on the vbat line while others should not give a beep sound.
This is only for short confirmation, how then do we get the exact shorted component
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 of freeze spray or paste.
- Voltage injection.
- Thermal camera.
Visual inspection
Many of the times when circuit component get short like capacitor 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 sign of burns on one corner, a diode would leave it's 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 sign 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 lead 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 give 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.
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| Freeze spray on circuit board. Photo credit_LaxyFix |
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 cause 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.
- Use multimeter or thermal camera to detect and confirm residue shorts.
- Remove only faulty capacitors, replace any diode that shows sign of a short.
- Remove and replace IC that shows sign of short.
Recommended Video guide on how to track short circuit:
Conclusion
Although shorts sometimes can be an arduous task to do, it is very easy to solve when you follow the right steps and pace. Most common cause of shorts are capacitors and ICs, diodes is not a very common cause of shorts. I believe by now you have had full knowledge about shorts and how you can solve every short circuit that comes your way. If any part of this article remain unclear to you do let us know via comment box.
