Mechanical damage usually reveals an external examination. In the case of our power supply, the problem was with the cable at the base of the magnetic connector. If the cable looks intact on the outside, then the damage may be inside the insulation or connector.
Be careful and try not to use a faulty power supply, it can be dangerous for your laptop and your health!
We proceed to replace the cable with a new one. To do this, you will need to disassemble the power supply and replace the old cable with a new one by soldering it.
Step 2 - Disassembling the Power Supply
To gain access to the insides of the power supply, it is necessary to separate the two halves that make up the block body. The halves are glued together, so you have to use force.We open the brackets designed for winding the cable when transporting the unit. We insert the pliers, as shown in the illustration, and unclench them with a little effort until the body halves begin to diverge from each other. We repeat the procedure on the other side.
Step 3 - Preparing the cable for desoldering
Next, we open the case completely. 
Step 4 - Preparing the cable for desoldering
Carefully open the copper shield covering the insides of the power supply. 
Step 5 - Cutting the Cable
Be careful, the screen is attached to the board with one leg, do not damage it. 
Step 6 - Soldering the cable
We solder the cable wires from the board. To simplify soldering, we recommend using soldering acid. Next, solder the new cable. 
Step 7 - Assembling the Power Supply
We assemble the halves of the power supply using glue for plastic products. We use universal super glue brand "Moment".For convenience, we used the Spudger tool, which applied glue to one of the halves of the block.
Have you ever thought about how you can fix the charger in the tundra?
Let's consider a hypothetical situation. You are a hipster with a Macbook and a geologist as well. You arrived somewhere far, far away and safely broke the charger, sit crying, where is now to process pictures and write essays.
But the problem has a solution
All you need after you listen to your colleagues and throw away half the unnecessary parts is: an eraser, a mosquito coil, pins, a knife, electrical tape.
First of all, a little theory.
A key feature of the Macbook's magnetic memory plug is that it can be inserted in either direction. Well, it's actually magnetic, yes. The effect is achieved as follows:
The first and fifth contacts come from the outer braid. The second and fourth branches off from the inner one. Thus, no matter how you stick it, you can’t confuse plus with minus. The outer remains outer, the inner remains inner.
There is no magnet in the connector. It's on a Macbook.
So what to do?
To begin with, cut the pins that will become contacts in the future. Then take a couple and pierce the eraser with them. Next, it should be cut to the maximum. The main task at this stage is to fix the pins in a certain position.
After that, we carefully make a form from the remaining eraser, which will be a platform for all our contacts, both external and internal. We outline what goes where and stick the existing structure so that the sharp ends form the same contacts. Then we cut them off safely.
When, after the fourteenth time, it turns out to stick them where they should, we begin the next stage. We wrap this story first with an internal braid, and then with tape.
From the tenth time it will turn out to do it neatly. Here, in general, and all.
If you find that your battery Macbook Pro no longer charges from the native adapter, do not rush to poke a soldering iron into it. As silly as it sounds, the first thing to do is:
1. make sure that the contact in the socket is reliable (do not use a broken one);
2. make sure that there is power in the outlet (plug another, known to be working device into it);
3. check that foreign objects are not packed into the laptop's power socket (usually food crumbs, compressed dust clods and other insects get there);
4. carefully inspect the yellow contacts of the connector. They should not be burnt, blackened, oxidized. When you try to drown them inward, the pins should come back without jamming. It is advisable not to scratch the gilded coating once again;
5. make sure that the cord from the adapter to the connector does not have mechanical damage, creases, bare wires do not stick out from under the insulation, have not been driven over by an office chair, etc. A damaged wire can be easily replaced with your own hands for any other of the appropriate section. In macbooks, only two wires go from the power supply to the Magsafe 2 connector:
If you are a very lucky person, simply unplugging the adapter from the network for a few minutes can save you. It happens that, due to a power surge, the charger goes into protection and it needs time to think the lock has been reset.
Sometimes, when you connect the adapter to your Macbook, the charging indicator does not light up, but in fact it is charging. The fact is that the desired indicator (orange or green) is set on fire on command from the SMC system management controller located in the MacBook. Sometimes, due to accumulated errors, the SMC starts to fail and then resetting the controller helps.
To do this, you need to connect the adapter to a completely turned off (not sleeping, namely turned off) macbook, press the key combination Shift + Control + Option and, without releasing them, press Power. Then, simultaneously releasing all the buttons, turn on the laptop with the reset controller. 
If all else fails, you will have to make a friend with the exact same MacBook and discreetly swap chargers with him and try to connect to his charger. It is not necessary that a friend has exactly the same adapter - a more powerful one will also work. The main thing here is that the connectors match. [Comment : according to one of the comments to this article, less than powerful block power supply is also suitable for testing]
If your MacBook battery does not charge with your charger, and when you connect someone else's charger, everything starts working as it should, then your charger is broken. Your cap. The bravest ones can tell the wife that the purchase of a mink coat is again canceled, since the MacBook is more important. The rest will have to repair the adapter on their own.
I had a defective 60W MagSafe 2 PSU, so most of the following will be true for this adapter. The 13-inch MacBook Pro with Retina screen was equipped with this charger:
- MD212, MD213 (Late 2012)
- MD212, ME662 (Early 2013)
- ME864, ME865, ME866 (late 2013)
- MGX72, MGX82, MGX92 (Mid 2014)
- MF839, MF840, MF841, MF843 (early 2015);
Macbook Pro Charging Repair
Before delving into the innards, it is useful to know how the charging process is initiated. You may be surprised, but Apple engineers have managed to integrate microprocessor control even into such a simple device as a charger. Here are the key points:
- operating voltage is 16.5 volts. However, as long as the adapter is not connected to a load, its output has an idle voltage (about 3V) with a current limit of ~0.1 mA;
- after connecting the connector to the macbook, the adapter output is loaded with a calibrated resistive load, due to which the open-circuit voltage sags to ~ 1.7V. The 16-bit microcontroller in the charger detects this fact and after 1 second instructs the output switches to output full voltage. Such difficulties make it possible to avoid sparking and burning of the connector contacts when the charger is connected to the laptop;
- when connecting too large a load, as well as in the presence of a short circuit, the open-circuit voltage will drop significantly below 1.7V and the command to turn on will not follow;
- in the power connector of the Macbook Pro there is a DS2413 microchip, which immediately after connecting to the MacBook starts exchanging information with the SMC controller via the 1-Wire protocol. The exchange takes place on a single-wire bus (the middle contact of the connector). The charger tells the laptop information about itself, including its power and serial number. The laptop, if everything suits it, connects its internal circuits to the adapter and tells it the current mode of operation, on the basis of which one of the two LEDs lights up in the connector. The entire exchange of pleasantries takes less than 100 milliseconds;
Considering the foregoing, it is unlikely that it will be possible to charge a MacBook without native charging. Checking the power supply without a MacBook will not work either. 
Theoretically, for testing, you can connect a 39.41 kΩ resistor to the two extreme contacts of the Magsafe connector (which is not so easy to do, given the design of the connector). After a second, a voltage of 16.5 volts should appear on the resistor. In this case, the indicator on the connector will not light.
For those who don't know, the Apple Magsafe 2 power supply connector has the following pinout: 
This smart design of the charging socket allows you to connect your Macbook without thinking about polarity.
Despite the fact that the original adapter has all kinds of foolproofing built in, it should still not be treated lightly. The power of this power supply is enough to set you on fire at the first opportunity, splash you with molten metal and scare you to hell ... hiccups.
How to painlessly disassemble the adapter
To disassemble the Macbook charger, you will have to use brute force, since the halves of the case are glued to each other. The most painless option is to use pliers as shown in this video:
I managed to disassemble the power supply from my Macbook Pro in 2-3 minutes (with most of the time spent looking for a convenient stop for the pliers). After that, light traces of the autopsy still remain: 
After the case is opened, you need to carefully inspect the printed circuit board for burnt tracks, charred resistors, swollen or leaking electrolytes, and other anomalies.
The board will most likely be filled with some kind of compound, it must be carefully removed. And it would be nice not to tear off anything superfluous. 
It does not hurt to immediately ring the fuse at 3.15A. Here it is in brown: 
If the fuse is defective, then this, as a rule, indicates a breakdown of either the diode bridge, or the powerful MOSFET, or both. These elements burn most often, since they bear the main load. They are very easy to find - they are located on a common radiator. 
If knocked out field-effect transistor, it makes sense to check the low-resistance resistor in the source circuit and the entire snubber circuit (R5, R6, C3, C4, D2, two chokes FB1, FB2 and capacitor C7): 
When repairing a Macbook power supply, it is strongly recommended to plug it into a 220V network through a 60-watt light bulb. This will prevent devastating consequences in the event of a short circuit in the circuit. 
Be extremely careful! A high-voltage capacitor can hold a life-threatening voltage for a long time. I got caught once and it was extremely frustrating.
If, after replacing the defective elements, the power supply did not start, then, alas, further repairs The Apple Magsafe 2 charger is not possible without an electrical circuit diagram.
By the way, the most reliable way to find out whether the circuit has worked or not is to measure the voltage on the output electrolytes. On the working adapter there should be 16.5V: 
Magsafe 2 Adapter Schematic (60 Watts)
Find circuit diagram Macbook power supply failed, so there was nothing left to do but copy it from printed circuit board. Here is the most interesting part: 
As can be seen from the diagram, the charger is assembled according to the classical scheme of a single-cycle switching power supply. The heart of the converter is the DAP013F chip - a modern quasi-resonant controller that allows you to achieve high efficiency, low interference, and also implement protection against overload, overvoltage and overheating. 
At the initial moment of time, after connecting the adapter to the outlet, there is no voltage on the turns of the winding 1-2, respectively, the voltage at the gate of the transistor Q33 is zero, and it is closed. At its drain, the voltage is equal to the operating voltage of the zener diode ZD34, which comes there from a full-wave rectifier formed by diodes D32, D34 and part of the power diode bridge BD1, through a chain of resistors R33, R42.
Transistor Q32 is open and capacitor C39 starts charging from the same diode rectifier (along the circuit: R44 - ZD36 - Q32). The voltage from this capacitor is supplied to the 14th leg of the IC34 microcircuit, which, through its internal switch, is connected to pin 10 and, accordingly, to the 22 uF electrolytic capacitor C (we could not find its designation on the board). The initial charging current of this capacitor is limited to 300 μA, then, when the voltage reaches 0.7V on it, the current increases to 3-6 mA.
When the microcircuit start voltage is reached on the capacitor C (about 9V), the internal generator starts, the pulses from the 9th output of the microcircuit arrive at the Q1 gate, and the whole circuit comes to life.
From this point on, the voltage of the IC34 microcircuit is powered by the capacitor C, the voltage on which is formed from the winding 1-2 of the transformer through the rectifier diode D31. In this case, the internal switch of the microcircuit breaks the connection between the 14th and 10th pins.
Protection against excessive increase in output power is implemented using elements ZD31 - R41 - R55. When the voltage at the output of the winding 1-2 rises above the breakdown voltage of the zener diode, a negative potential appears on the 1st output of the microcircuit, which leads to a proportional decrease in the amplitude of the pulses on the 9th output.
Overheating protection is implemented using an NTC31 thermistor connected to the 2nd output of the microcircuit.
The 4th output of the microcircuit is used to determine the moment of switching the output key at the points of minimum current.
The 6th output of the microcircuit is designed to stabilize the output voltage of the adapter. The feedback loop includes an IC131 optocoupler that performs galvanic isolation high and low voltage parts of the adapter. If the voltage on the 6th leg drops below 0.8V, the converter switches to reduced power mode (25% of the nominal). Capacitor C36 is required for correct operation in this mode. To return to normal operation, the voltage on the 6th leg must rise above 1.4V.
The 7th leg of the microcircuit is connected to the current sensor R9 and if a certain threshold is exceeded, the operation of the converter is blocked. Capacitor C34 sets the time interval for the auto-recovery system after an overcurrent.
Pin 12 of the microcircuit is designed to protect the circuit from overvoltage. As soon as the voltage on this leg exceeds 3V, the microcircuit goes into blocking and will remain in this state until the voltage on capacitor C drops below the controller reset level (5V). To do this, you need to unplug the adapter from the network and wait a while.
It seems that this adapter does not use the overvoltage protection functionality built into the microcircuit (in any case, I was not able to trace what the R53 resistor is connected to). Apparently, this role is assigned to the transistor Q34, included in the feedback circuit in parallel with optocoupler IC131. The transistor is controlled by the voltage from winding 1-2 through a resistive divider R51-R50-R43 and in the event of, for example, an optocoupler malfunction, it will not allow the microcircuit to increase the converter voltage uncontrollably.
Thus, this 60-watt power adapter implements triple protection against exceeding the output voltage of acceptable limits: an optocoupler in the feedback circuit, a Q34 transistor in the same circuit, and a ZD31 zener diode connected to the 1st leg of the microcircuit. Add here more protection against overheating and overcurrent (against short circuit). It turns out a very reliable and safe charger for a MacBook.
In Chinese chargers, most of the protection systems are thrown away, and also, in the interests of economy, there are no circuits for filtering RF interference and eliminating static electricity. And although these crafts are quite efficient, you have to pay for their cheapness with a higher level of interference and an increased risk of failure of the laptop power board.
Now, having the circuit in front of your eyes and imagining how it should work, it will be easy to find and fix any malfunction.
In my case, the inoperability of the adapter was caused by an internal break in the resistor R33, due to which the Q32 transistor was always locked, the voltage was not supplied to the 14th leg of the controller, respectively, the voltage on the capacitor FROM could not reach the chip enable level. 
After soldering the R33 resistor, the microcircuit start circuit was restored and the circuit started working. I hope that this article will help you fix the charger from your MacBook Pro.
For help in identifying completely burned out elements, I am attaching an archive with photos of the board in high resolution(37 photos, 122 Mb).
And people dissected exactly the same charger, only with a power of 85 watts. Also interesting. 
Have you ever wondered what is inside the MacBook charger? There are far more parts in the compact power supply than you might expect, including even a microprocessor. In this article, you and I will be able to disassemble the MacBook charger to see the many components hidden inside and find out how they interact to safely deliver much-needed electricity to the computer.
Most consumer electronics, from your smartphone to your TV, use switching power supplies to convert AC power from a wall outlet to low voltage. direct current used by electronic circuits. Switching power supplies, or more correctly, low-voltage power supplies, get their name from the fact that they turn the power supply on and off thousands of times per second. It is the most efficient for voltage conversion.
The main alternative to the switching power supply is the linear power supply, which is much simpler and converts surge voltage into heat. Due to this energy loss, the efficiency of a linear power supply is about 60%, compared to about 85% for a switching power supply. Linear power supplies use a bulky transformer that can weigh up to a kilogram or more, while switching power supplies can use tiny high frequency transformers.
Now these power supplies are very cheap, but this was not always the case. In the 1950s, switching power supplies were complex and expensive, used in aerospace and satellite technologies who needed a light and compact power source. By the early 1970s, new high-voltage transistors and other technological improvements made sources much cheaper and widely used in computers. The introduction of single-chip controllers in 1976 made power converters even simpler, smaller, and cheaper.
Apple's use of switching power supplies began in 1977, when chief engineer Rod Holt designed the switching power supply for the Apple II.
According to Steve Jobs:
This switching power supply was as revolutionary as the Apple II logic. Rod did not receive much recognition in the pages of history, but he deserved it. Every computer now uses switching power supplies, and they are all similar in design to Holt's design.
It's a great quote, but it's not entirely true. The power supply revolution happened much earlier. Robert Boschert started selling switching power supplies in 1974 for everything from printers and computers to the F-14 fighter jet. Apple's design was similar to earlier devices and other computers did not use Rod Holt's design. However, Apple is making extensive use of switching power supplies and pushing the boundaries of charger design with compact, stylish and advanced chargers.
What is inside?
The Macbook 85W charger model A1172 was taken for analysis, the dimensions of which are small enough to fit in the palm of your hand. The figure below shows a few features that can help distinguish an original charger from fakes. A bitten apple on the case is an essential attribute (which everyone knows about), but there is a detail that does not always attract attention. Original chargers must have a serial number located under the ground contact.
As strange as it may sound, but The best way open the charge - use a chisel or something similar and add a little brute force to it. Apple was initially opposed to someone opening up their products and inspecting the “insides”. Removing the plastic case, you can immediately see the metal radiators. They help cool the powerful semiconductors housed inside the charger.
On the back of the charger, you can see the printed circuit board. Some tiny components are visible, but most of the circuitry is hidden under a metal heatsink held together with yellow electrical tape.
We looked at the radiators and that's enough. To see all the details of the device, of course, you need to remove the radiators. There are far more components hidden under these metal parts than one would expect from a small block.
The image below shows the main components of the charger. AC power enters the charger and is already converted to direct current there. PFC (Power Factor Correction) circuitry improves efficiency by ensuring a stable load on the AC lines. According to the feasible functions, the board can be divided into two parts: high-voltage and low-voltage. The high-voltage part of the board, together with the components placed on it, is designed to lower the high-voltage direct voltage and transfer it to the transformer. The low-voltage part receives a constant low-voltage voltage from the transformer and outputs a constant voltage of the required level to the laptop. Below we consider these schemes in more detail.
AC input to charger
AC voltage is supplied to the charger through a removable plug network cable. A big advantage of switching power supplies is their ability to operate over a wide range of input voltages. By simply changing the plug, the charger can be used in any region of the world, from European 240 volts at 50 hertz to North American 120 volts at 60 hertz. Capacitors, filters and inductors at the input stage prevent interference from leaving the charger through the power lines. The bridge rectifier contains four diodes that convert AC power to DC.Watch this video for a better demonstration of how a bridge rectifier works.
PFC: power smoothing
The next step in the operation of the charger is the power factor correction circuit, marked in purple. One problem with simple chargers is that they only get charged for a small portion of the AC cycle. When a single device does this, there are no particular problems, but when there are thousands of them, it creates problems for energy companies. This is why regulations require chargers to use power factor correction (they use power more evenly). You might expect poor power factor to be caused by switching power transmission that turns on and off quickly, but this is not a problem. The problem comes from the non-linear diode bridge, which only charges the input capacitor when the AC signal peaks. The idea behind the PFC is to use a DC boost converter before switching the power supply. Thus, the current sine wave at the output is proportional to the AC waveform.The PFC circuit uses a power transistor to accurately churn the AC input tens of thousands of times per second. Contrary to expectations, this makes the load on the AC lines smoother. The two largest components in a charger are the inductor and the PFC capacitor, which help boost the DC voltage to 380 volts. The charger uses the MC33368 chip to run the PFC.
Primary power conversion
The high voltage circuit is the heart of the charger. It takes the high DC voltage from the PFC circuit, chops it up, and feeds it into a transformer to generate a charger's low voltage output (16.5-18.5 volts). The charger uses an advanced resonant controller that allows the system to operate at very high frequencies up to 500 kilohertz. The higher frequency allows more compact components to be used inside the charger. The IC shown below controls the power supply.SMPS controller - high-voltage resonant controller L6599; labeled DAP015D for some reason. It uses a half-bridge resonant topology; in a half-bridge circuit, two transistors drive power through the converter. Common switching power supplies use a PWM (Pulse Width Modulation) controller that corrects the input time. L6599 corrects the frequency of the pulse, not its pulse. Both transistors turn on alternately for 50% of the time. When the frequency increases higher resonant frequency, the power drops, so the frequency control adjusts the output voltage.
The two transistors alternately turn on and off to lower the input voltage. The transducer and capacitor resonate at the same frequency, smoothing the interrupted input into a sine wave.
Secondary power conversion
The second half of the circuit generates the output of the charger. It receives power from the converter and with the help of diodes, converts it into direct current. Filter capacitors smooth out the voltage that comes from the charger through the cable.The most important role of the low voltage parts of the charger is to keep the dangerous high voltage inside the charger to avoid potentially damaging shock to the end device. The insulating gap, marked with a red dotted line in the image above, indicates the separation between the main high voltage part and the low voltage part of the device. Both sides are separated from each other by a distance of about 6 mm.
The transformer transfers power between the primary and secondary devices using magnetic fields, instead of direct electrical connection. The wire in the transformer is triple insulated for safety. Cheap chargers tend to be stingy with insulation. This poses a security risk. The optocoupler uses an internal light beam to transmit a feedback signal between the low voltage and high voltage parts of the charger. The control circuit in the high voltage part of the device uses the feedback signal to adjust the switching frequency to keep the output voltage stable.
Powerful microprocessor inside charger
The unexpected component of the charger is a miniature circuit board with a microcontroller, which can be seen in our schematic above. This 16-bit processor constantly monitors charger voltage and current. It enables transmission when the charger is connected to the MacBook and disables transmission when the charger is disconnected. Disconnecting the charger occurs if there is any problem. This is a Texas Instruments MSP430 microcontroller, about the same power as the processor inside the first original Macintosh. The processor in the charger is a low power microcontroller with 1 KB of flash memory and only 128 bytes of RAM. It includes a high-precision 16-bit A/D converter.The 68000 microprocessor from the original Apple Macintosh and the 430 microcontrollers in the charger are not comparable because they have various designs and instruction sets. But for a rough comparison, the 68000 is a 16/32 bit processor running at 7.8MHz, while the MSP430 is a 16 bit processor running at 16MHz. The MSP430 is designed for low power consumption and uses approximately 1% of the 68000's power supply.
The gold-plated pads on the right are used for programming the chip during production. The 60W MacBook charger uses an MSP430 processor, but the 85W charger uses a general purpose processor that needs to be flashed. It is programmed with the Spy-Bi-Wire interface, which is a two-wire version of the TI standard JTAG interface. Once programmed, the safety fuse in the chip is destroyed to prevent the firmware from being read or modified.
The three pin IC on the left (IC202) reduces the charger's 16.5 volts to the 3.3 volts required by the processor. The voltage to the processor is provided not by a standard voltage regulator, but by the LT1460, which delivers 3.3 volts with an exceptionally high accuracy of 0.075%.
Lots of tiny components on the underside of the charger
Flipping the charger upside down on the circuit board reveals dozens of tiny components. The PFC and Power Supply Controller Chip (SMPS) are the main integrated circuits that control the charger. The voltage reference chip is responsible for maintaining a stable voltage even when the temperature changes. Voltage reference chip, it is TSM103/A which combines two operational amplifiers and a 2.5V reference in a single chip. The properties of a semiconductor vary greatly with temperature, so maintaining a stable voltage is not an easy task.These microcircuits are surrounded by tiny resistors, capacitors, diodes and other small components. MOS - output transistor, turns the power on and off at the output in accordance with the instructions of the microcontroller. To the left of it are resistors that measure the current being sent to the laptop.
An isolation gap (marked in red) separates the high voltage from the low voltage output circuit for safety. The dotted red line shows the insulation boundary that separates the low voltage side from the high voltage side. Optocouplers send signals from the low-voltage side to the main unit, shutting down the charger if there is a problem.
A little about grounding. A 1KΩ ground resistor connects the AC ground terminal to the ground at the output of the charger. Four 9.1MΩ resistors connect the internal DC base to the output base. Since they cross the isolation boundary, security is a concern. Their high stability avoids the danger of shock. The four resistors are not really required, but the redundancy is there to ensure the safety and fault tolerance of the device. There is also a Y capacitor (680pF, 250V) between internal ground and output ground. T5A fuse (5A) protects the ground output.
One of the reasons to install more control components in the charger than usual is the variable output voltage. To deliver 60 watts of voltage, the charger provides 16.5 volts with a resistance level of 3.6 ohms. To deliver 85 watts, the potential rises to 18.5 volts and the resistance is 4.6 ohms, respectively. This allows the charger to be compatible with laptops that require different voltages. As the current potential rises above 3.6 amps, the circuit gradually increases the output voltage. The charger will shut down automatically when the voltage reaches 90W.
The control scheme is quite complex. The output voltage is controlled by the operational amplifier in the TSM103/A chip, which compares it with the reference voltage generated by the same chip. This amplifier sends a feedback signal through an optocoupler to the SMPS control chip on the high voltage side. If the voltage is too high, the feedback signal lowers the voltage and vice versa. This is a fairly simple part, but where the voltage goes from 16.5 volts to 18.5 volts things get more complicated.
The output current creates a voltage across resistors with a tiny resistance of 0.005Ω each - they are more like wires than resistors. The operational amplifier in the TSM103/A chip amplifies this voltage. This signal goes to a tiny TS321 op amp which starts ramping up when the signal is 4.1A. This signal enters the previously described control circuit, increasing the output voltage. The current signal also enters a tiny TS391 comparator which sends a signal to the high voltage device via another optocoupler to cut the output voltage. This is a protection circuit if the current level gets too high. There are several places on the PCB where zero resistance resistors (i.e. jumpers) can be placed to change the gain of the op amp. This allows the gain accuracy to be adjusted during fabrication.
Magsafe plug
The Magsafe magnetic plug that plugs into your Macbook is more complex than it might first appear. It has five spring-loaded pins (known as Pogo pins) for connection to the computer, as well as two power pins, two ground pins. The middle pin is the data connection to the computer.
Inside, Magsafe is a miniature chip that tells the laptop the serial number, type, and power of the charger. The laptop uses this data to determine the originality of the charger. The chip also controls LED indicator for visual definition states. The laptop does not receive data directly from the charger, but only through a chip inside Magsafe.
Charger usage
You may have noticed that when you connect the charger to your laptop, it takes one or two seconds before the LED sensor fires. During this time, there is a complex interaction between the Magsafe plug, the charger, and the Macbook itself.When the charger is disconnected from the laptop, the output transistor blocks the voltage to the output. If you measure the voltage from the MacBook charger, you will find approximately 6 volts instead of the 16.5 volts you were hoping to see. The reason is the output is disconnected and you are measuring the voltage across the bypass resistor just below the output transistor. When the Magsafe plug is plugged into the Macbook, it starts to draw low voltage. The microcontroller in the charger detects this and turns on the power supply within a few seconds. During this time, the laptop manages to get all the necessary information about the charger from the chip inside Magsafe. If all is well, the laptop starts to consume power from the charger and sends a signal to the LED indicator. When the Magsafe plug is disconnected from the laptop, the microcontroller detects the loss of current and turns off the power supply, which also extinguishes the LEDs.
A perfectly logical question arises - why is the Apple charger so complicated? Other laptop chargers simply provide 16 volts and supply voltage immediately when connected to a computer. The main reason is for security purposes, to ensure that no voltage is applied until the pins are firmly attached to the laptop. This minimizes the risk of sparks or electric arcs when a Magsafe plug is connected.
Why You Shouldn't Use Cheap Chargers
The original Macbook 85W charger costs $79. But for $14 you can buy a charger on eBay that looks like the original. So what do you get for the extra $65? Let's compare the copy of the charger with the original. From the outside, the charger looks exactly like Apple's original 85W. Except that the Apple logo itself is missing. But if you look inside, the differences become obvious. The photos below show a genuine Apple charger on the left and a copy on the right.
A copy of the charger has half as many parts as the original and the space on the printed circuit board is simply empty. While the genuine Apple charger is chock-full of components, the replica isn't designed for much filtering and regulation and lacks PFC circuitry. The transformer in the copy of the charger (large yellow rectangle) is much larger in size original model. The higher frequency of the Apple Advanced Resonant Converter allows the use of a transformer smaller.
Turning the charger upside down and examining the printed circuit board reveals the more complex circuitry of the original charger. The copy has only one control IC (in the upper left corner). Since the PFC circuit is completely thrown away. In addition, the charging clone is less difficult to manage and does not have a ground connection. You understand what it threatens.
It is worth noting that the copy of the charger uses a Fairchild FAN7602 green PWM controller chip, which is more advanced than you might expect. I think most people expected to see something like a simple transistor oscillator. And in addition to the copy, unlike the original, a single-sided printed circuit board is used.
Actually a copy of the charger best quality than you might expect, compared to the terrible copies of iPad and iPhone chargers. MacBook charger copy doesn't cut everything possible components and uses a moderately complex circuit. There is also a slight emphasis on safety in this charger. Isolation of components and separation of high and low voltage sections are applied, except for one dangerous mistake, which you will see below. The Y capacitor (blue) was mounted crookedly and dangerously close to the optocoupler contact on the high voltage side, creating a risk of electric shock.
Problems with the original from Apple
The irony is that despite the complexity and attention to detail, the charger Apple device The MacBook is not a failsafe device. On the Internet you can find a lot of various photos of burnt, damaged and simply non-working chargers. The most vulnerable part of the original charger is the wire near the Magsafe plug. The cable is quite flimsy and it frays quickly, which leads to damage, burnout or simply breaking. Apple provides ways to avoid damaging the cable instead of just providing a more powerful cable. As a result of the review on the website Apple the charger received only 1.5 stars out of 5 possible.
MacBook chargers can also stop working due to internal issues. The photos above and below show burn marks inside Apple's failed charger. Unfortunately, it is impossible to say exactly what caused the fire. Due to the short circuit, half of the components burned out and a good part of the printed circuit board. Below in the photo is a burnt silicone insulation for mounting the board.
Why are original chargers so expensive?
As you can see, the Apple charger has a more advanced design than the copies and has additional functions for security. However, a genuine charger costs $65 more and I doubt that additional components cost more than $10 - $15. Much of the cost of the charger goes into the company's bottom line. An estimated 45% of the cost of the iPhone is the company's net profit. Probably, chargers bring in even more funds. The price of the original from Apple should be much lower. The device has many tiny components of resistors, capacitors, and transistors that range in price in the region of one cent. Large semiconductors, capacitors, and inductors naturally cost significantly more, but for example, a 16-bit MSP430 processor costs only $0.45. Apple explains the high cost not only by the cost of marketing and so on, but also by the high costs of developing a particular charger model itself. BookHave you ever wondered what's inside a MacBook charger? Indeed, a very large and complex circuit was squeezed into a compact power supply, including microcontrollers. This charger works to charge and power a laptop.
Most consumer electronics devices, from mobile phone to the TV, use a switching power supply to convert AC from a 220V outlet to low voltage DC into electronic circuits. Impulse block power gets its name from the fact that it switches state thousands of times per second, which turns out to be very effective way implementation of voltage conversion.
Switching power supplies are very cheap now, but that wasn't always the case. As recently as 40 years ago, switching power supplies were complex and expensive, used primarily in aerospace and satellite applications that needed small, lightweight power supplies. By the early 1980s, new high-voltage transistors and other technologies made switching power supplies much cheaper, and they were widely used in computers.
Apple makes extensive use of switching power supplies, and this principle has created a charger with a compact and advanced circuit design.
Inside the charger
The power supply for a MacBook 85w, model for the a1172, has been opened and is small enough to fit in the palm of your hand. The picture below shows a few features that make it possible to distinguish a charger from a fake: the Apple logo in the case of metal (not plastic), and the serial number next to the "ground" contact.
Oddly enough, the easiest way to open a PSU is to run a chisel around the connecting seam to pry it open. Heat sinks for cooling high-power semiconductors are visible after disassembly inside the charger.
The diagram below shows the main components of the charger. AC power enters the charger and is converted to DC. The PFC (Power Factor Correction) circuit improves efficiency by keeping the load on the AC lines stable. The high DC voltage from the corrector is fed into the transformer. The secondary part receives low-voltage power from a transformer, and the outputs are DC voltage for a laptop.
Click to enlarge diagram
Alternating current enters the charger through a removable mains plug. A big advantage of switching power supplies is that they can be designed to run on a wide range of input voltages. By simply changing the plug, the charger can be used in any region of the world, from European 240 volts at 50 Hertz to North America with 120 volts at 60 Hz. Filter capacitors and inductors in the input section prevent interference from the output of the charger through the 220 V lines. The bridge rectifier contains four diodes that convert alternating current into permanent.
The primary circuit is the heart of the charger. It injects a high DC voltage into the PFC circuit, and then feeds it to the transformer to create a low voltage output (16.5-18.5 volts). The PSU uses a resonant controller that allows the system to operate at very high frequencies, up to 500 kilohertz. The high frequency allows the use of smaller components for a more compact charger design. The chip in the photo below controls pulsed source nutrition.
The secondary receives power from the transformer and converts it to DC with diodes. The filter capacitors smooth out the power that leaves the charger through the output cable.
It is important to keep dangerous high voltages away from the exit to avoid fatal problems. The insulation boundaries marked in red in the diagram show the separation between the high voltage and the main low voltage part. Both sides are about 6 mm apart and only special components can cross this boundary.
Click to enlarge diagram
The transformer reliably transfers power between the primary and secondary unit using a magnetic field instead of a direct electrical connection. The coils of wire inside the transformer are triple insulated for safety. Cheap imitation chargers tend to skimp on insulation which can pose a safety hazard.
The control IC uses the feedback signal to adjust the switching frequency and keep the output voltage stable.
Powerful charger microprocessor
One of the interesting components is the tiny microcontroller board seen above. This 16-bit processor constantly monitors the voltage and current of the charger, allowing the output to shut off when the charger is disconnected from the MacBook. it msp430 microcontroller. It was not possible to find a complete scheme, although for this it took 2 hours to shovel dozens of sites on electronics, so if you have it, please send it.
The magsafe magnetic connector that plugs into the MacBook is more complex than one might expect. It has five spring-loaded pins for connecting to a laptop. The two power contacts of the two extreme pins are duplicated, and the middle contact is for data transfer to the laptop. So you can not think about the polarity - connect as you want.
There is a tiny chip inside the magsafe connector that informs the laptop about the charger type: serial number, model and power. The laptop uses this data to determine if the charger is valid for normal operation. This chip also controls the state of the LEDs.
Why You Shouldn't Buy a Cheap Charger
At 85W, the MacBook charger costs $80, but for $15 you can buy a device on eBay that looks identical. Be careful - on the outside, the charger looks just like the 85W from Apple, even the name and logo will be there. But looking inside reveals big differences. The photos above show the original Apple and the copy on the right side.
Discuss the article CHARGING PSU FOR APPLE MACBOOK