Electrical diagram of the charger for nokia ac 15. Repair and modification of the charger for NOKIA cell phones. Chargers from other manufacturers

Most modern network chargers are assembled using a simple pulse circuit, using one high-voltage transistor (Fig. 1) according to a blocking generator circuit.

Unlike simpler circuits using a step-down 50 Hz transformer, the transformer for pulse converters of the same power is much smaller in size, which means the size, weight and price of the entire converter are smaller. In addition, pulse converters are safer - if in a conventional converter, when the power elements fail, the load receives a high unstabilized (and sometimes even alternating) voltage from the secondary winding of the transformer, then in case of any malfunction of the “pulse generator” (except for the failure of the reverse optocoupler connection - but it is usually very well protected) there will be no voltage at the output at all.

Rice. 1
A simple pulse blocking oscillator circuit

A detailed description of the principle of operation (with pictures) and calculation of the circuit elements of a high-voltage pulse converter (transformer, capacitors, etc.) can be read, for example, in “TEA152x Efficient Low Power Voltage supply” at the link http://www. nxp.com/acrobat/applicationnotes/AN00055.pdf (in English).

The alternating mains voltage is rectified by diode VD1 (although sometimes the generous Chinese install as many as four diodes in a bridge circuit), the current pulse when turned on is limited by resistor R1. Here it is advisable to install a resistor with a power of 0.25 W - then if overloaded, it will burn out, acting as a fuse.

The converter is assembled on transistor VT1 using a classic flyback circuit. Resistor R2 is needed to start generation when power is applied; in this circuit it is optional, but with it the converter works a little more stable. Generation is maintained thanks to capacitor C1, included in the PIC circuit on the winding, the generation frequency depends on its capacitance and the parameters of the transformer. When the transistor is unlocked, the voltage on the lower terminals of windings I and II in the diagram is negative, on the upper ones it is positive, the positive half-wave through capacitor C1 opens the transistor even more strongly, the voltage amplitude in the windings increases... That is, the transistor opens like an avalanche. After some time, as capacitor C1 charges, the base current begins to decrease, the transistor begins to close, the voltage at the upper terminal of winding II in the circuit begins to decrease, through capacitor C1 the base current decreases even more, and the transistor closes like an avalanche. Resistor R3 is necessary to limit the base current during circuit overloads and surges in the AC network.

At the same time, the amplitude of the self-induction EMF through the diode VD4 recharges the capacitor SZ - that is why the converter is called flyback. If you swap the terminals of winding III and recharge the capacitor SZ during the forward stroke, then the load on the transistor will sharply increase during the forward stroke (it may even burn out due to too much current), and during the reverse stroke the self-induction EMF will be unspent and will be released by collector junction of the transistor - that is, it can burn out from overvoltage. Therefore, when manufacturing the device, it is necessary to strictly observe the phasing of all windings (if you mix up the terminals of winding II, the generator simply will not start, since capacitor C1 will, on the contrary, disrupt generation and stabilize the circuit).

The output voltage of the device depends on the number of turns in windings II and III and on the stabilization voltage of the zener diode VD3. The output voltage is equal to the stabilization voltage only if the number of turns in windings II and III is the same, otherwise it will be different. During the reverse stroke, capacitor C2 is recharged through diode VD2, as soon as it is charged to approximately -5 V, the zener diode will begin to pass current, the negative voltage at the base of transistor VT1 will slightly reduce the amplitude of the pulses on the collector, and the output voltage will stabilize at a certain level. The stabilization accuracy of this circuit is not very high - the output voltage varies within 15...25% depending on the load current and the quality of the zener diode VD3.
A circuit of a better (and more complex) converter is shown in rice. 2

Rice. 2
Electrical circuit of a more complex
converter

To rectify the input voltage, a diode bridge VD1 and a capacitor are used; the resistor must have a power of at least 0.5 W, otherwise at the moment of switching on, when charging capacitor C1, it may burn out. The capacitance of capacitor C1 in microfarads must be equal to the power of the device in watts.

The converter itself is assembled according to the already familiar circuit using transistor VT1. A current sensor on resistor R4 is included in the emitter circuit - as soon as the current flowing through the transistor becomes so large that the voltage drop across the resistor exceeds 1.5 V (with the resistance indicated on the diagram being 75 mA), transistor VT2 opens slightly through diode VD3 and limits the base current of transistor VT1 so that its collector current does not exceed the above 75 mA. Despite its simplicity, this protection circuit is quite effective, and the converter turns out to be almost eternal even with short circuits in the load.

To protect transistor VT1 from emissions of self-induction EMF, a smoothing circuit VD4-C5-R6 was added to the circuit. The VD4 diode must be high-frequency - ideally BYV26C, a little worse - UF4004-UF4007 or 1 N4936, 1 N4937. If there are no such diodes, it is better not to install a chain at all!

Capacitor C5 can be anything, but it must withstand a voltage of 250...350 V. Such a chain can be installed in all similar circuits (if it is not there), including in the circuit according to rice. 1- it will noticeably reduce the heating of the switch transistor housing and significantly “extend the life” of the entire converter.

The output voltage is stabilized using the zener diode DA1 located at the output of the device, galvanic isolation is provided by the optocoupler V01. The TL431 microcircuit can be replaced with any low-power zener diode, the output voltage is equal to its stabilization voltage plus 1.5 V (voltage drop across the LED of the optocoupler V01)’; a small resistance resistor R8 is added to protect the LED from overloads. As soon as the output voltage becomes slightly higher than expected, current will flow through the zener diode, the optocoupler LED will begin to glow, its phototransistor will open slightly, the positive voltage from capacitor C4 will slightly open transistor VT2, which will reduce the amplitude of the collector current of transistor VT1. The instability of the output voltage of this circuit is less than that of the previous one and does not exceed 10...20%; also, thanks to capacitor C1, there is practically no 50 Hz background at the output of the converter.

It is better to use an industrial transformer in these circuits, from any similar device. But you can wind it yourself - for an output power of 5 W (1 A, 5 V), the primary winding should contain approximately 300 turns of wire with a diameter of 0.15 mm, winding II - 30 turns of the same wire, winding III - 20 turns of wire with a diameter of 0 .65 mm. Winding III must be very well insulated from the first two; it is advisable to wind it in a separate section (if any). The core is standard for such transformers, with a dielectric gap of 0.1 mm. As a last resort, you can use a ring with an outer diameter of approximately 20 mm.
Download: Basic diagrams of pulse network adapters for charging phones
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Power supply

Repair and modification of NOKIA cell phone charger

As the number of mobile phones increases, the number of chargers included with the phones also increases proportionally. Given the poor quality of our electrical networks, these devices often fail. This especially applies to models of chargers from unknown manufacturers purchased on radio markets due to their low cost.

As a rule, to maintain profitability, such manufacturers use cheaper components in their devices, which inevitably entails a decrease in their reliability.

After a similar charger for a NOKIA phone purchased on the radio market failed after not even a week of operation, it was decided to find out the cause of the malfunction and make the necessary changes to the circuit to improve the reliability of the device as a whole.

It should be noted that when comparing two chargers - certified and "gray" - it is not easy to find the difference (Fig. 1). The case of a device from an unknown manufacturer (above in Fig. 1) is distinguished by less deeply embossed inscriptions of the NOKIA logo and technical characteristics of the device, as well as the absence of a silk-screened icon regulating the method of disposal of the device at the end of its service life. In Fig. Figure 2 shows the circuit board of the device.

The circuit diagram of the device was reconstructed from the circuit board. It is a classic pulse flyback converter (Fig. 3).

Such simple circuits are widely used in switching power supplies and chargers (power up to 25 W).

The declared characteristics of the device are an output voltage of 5.7 V and a load current of 800 mA.

Now let’s briefly look at the principle of operation of the power supply in the circuit diagram (Fig. 3).

The mains voltage is supplied through current-limiting resistor R1 to the input of the rectifier on diodes D1-D4. Transistor Q1 is used to create a self-oscillator, the frequency of which is mainly determined by the characteristics of the pulse transformer TF1 used here. Resistor R3 sets the operating mode of transistor Q1. Stabilization of the output voltage occurs through the use of the feedback winding of the pulse transformer TF1 and the circuit D7 C4 ZD1. Transistor Q2 and resistor R2 serve to limit the current of transistor Q1 at the moment the generator starts, as well as in the event of an overload or short circuit at the output of the device. The circuit contains a half-wave output voltage rectifier using diode D8 and capacitor C5. Resistor R6 serves to discharge capacitor C5 after the device is turned off.

As a result of checking the charger described above, a faulty transistor Q1 marked 1003 and a burnt resistor R3 were found. The burnt coating of the resistor made it impossible to determine its resistance. In order to increase the reliability of the circuit, a more powerful and widespread domestic transistor KT 940A was used as transistor Q1 (Fig. 4). It should be noted that due to the large variation in the characteristics of the KT 940A transistors, in some cases it may be necessary to change the value of resistance R3 indicated on the diagram.

It should be noted that on the board, in the place provided for this, there is no oxide capacitor C, which must be connected at the output of the diode rectifier D1-D4. In this case, the device’s self-oscillator actually operates in modulation mode with rectified mains voltage. For this reason, in many cases, such devices may not provide the stated output current required to charge a mobile phone battery. The consequence of this could be, for example, an increase in the total charging time. If necessary, you can install this missing capacitor - its capacity can be no more than 10 μF for an operating voltage of at least 450 V. It is recommended that immediately after installing the capacitor, solder a resistor with a resistance of about 300 kOhm parallel to its legs on the mounting side (to discharge this capacitor after disconnecting the device from networks). In addition, for reliability, it is advisable to use resistor R1 with a higher power dissipation, since it limits the charging current of the above capacitor when the device is turned on to the network. The board provides space for an LED designed to indicate the operation of the device and, if necessary, it can be installed on the board through a current-limiting resistor with a resistance of 680 Ohms.

After repair, this charger has been working reliably for more than a year without any problems. Considering that the converter circuit used is widely used in many chargers, the described method for repairing and increasing reliability can be recommended for other similar devices.

1. Lyrical digression

There are probably not many people left in the world who are not familiar with the Finnish company NOKIA. One of the main activities of which is the development, production and sale of cell phones.

Like any other company with a well-known name, it is a “tidbit” for various small (mainly Chinese) manufacturers who want to sell their products under someone else’s brand. Due to this, the news quite often contains reports of attempts to sell (sometimes more than successful) counterfeit electronic equipment. Such activity is illegal and negatively affects both the image of the original manufacturer and its financial condition.

However, in the vast majority of cases, it is ordinary consumers who suffer first because of this, which includes your humble servant. Because In the history of such counterfeits, there are practically no cases where the quality of counterfeit products was not inferior to the original ones. At the same time, the result of using counterfeit products can be not only moral or financial damage, but also harm to health.

It is no secret that most often manufacturers of “counterfeits” turn their attention to branded consumables and accessories. Because on the one hand, the production of such goods does not require large technical and production resources, and on the other hand, it allows you to receive tangible profits. Both due to the lower cost compared to original goods (which negatively affects the quality), and due to the counterfeit “brand”, because Even with comparable quality, products from well-known companies are more expensive. In the market of mobile communication devices, the first place in the number of counterfeits is probably occupied by rechargeable batteries. I don’t think it’s worth talking at length about the negative consequences of this state of affairs. A flaming battery can cause anything from fire to serious injury. However, today we will not talk about them, but about a related group of products - chargers.

When you buy a mobile phone, in 99.9% of cases it is already equipped with a wall charger. And everything would be great if you didn’t have to use it :). And since it needs to be used, there is a possibility that it will fail. It can be lost, a pet can chew the cable, etc.

In addition, it is convenient when there are several chargers. One can be used at home, another at work, and the third can be thrown at the dacha. This will allow you to charge your phone no matter where you are. I think everyone knows from their own experience that the phone tends to run out of charge at the most inopportune moment :).

I usually use two chargers, one at home and one at work. One charger is included with the phone, and a second one can be purchased. There are two options here - buy an original charger and a non-original one (not fake, but simply manufactured and sold under the brand name of another company) compatible with your phone model. An original charger guarantees full compatibility with your mobile phone and quality, but it is not always available for sale. And besides, it can cost significantly more than the non-original one (although not always). If there is both an original and non-original charger on sale, then the choice is up to the buyer. You can save some money, or you can financially support your “favorite” manufacturer :). With rare exceptions (this does not apply to mobile phones), I will choose the original charger.

2. Facts

Currently I am using a NOKIA E50 mobile phone. Almost immediately after purchasing the phone, I became concerned about purchasing a second charger. A charger model AC-4E was included with the phone. Using the services of one of the many online stores that sell mobile phones and accessories, I ordered a similar charger for myself, having previously clarified by phone that the chargers being sold were original and were sold in appropriate packaging. When purchasing, I inspected the device externally, the box matched the image on the NOKIA website, and the charger itself exactly matched the one I already had. I left it at work and used it from time to time to charge my phone. The charging process was slower, but... the difference was insignificant (~75 minutes versus 50), so I did not focus on this. At one point (after ~3.5 months) this charger burned out (with corresponding noise and smoke effects). There was a sharp click and the smell of burnt plastic.

Because I couldn’t find a warranty card, and there was no time to implement warranty obligations then, so I decided to buy a new charger, and I opened this one out of curiosity. By the way, disassembling a NOKIA charger is not an easy task, although, unlike the vast majority of chargers from other manufacturers, it provides for the possibility of disassembly. It's all about using screws with the original head. Neither a regular screwdriver, nor a Phillips, nor an asterisk, nor a hexagon will help you.

I have not yet come across such screwdrivers for sale; perhaps they are available in a specialized store that sells spare parts for mobile phones. As a result, after applying serious physical effort, I unscrewed the screws using a flat-head screwdriver of the appropriate size, but the screw heads were severely damaged. So there is no need to talk about the possibility of painlessly disassembling the charger. Which, in general, is good, because... on the one hand, it allows for prompt repair of the device, and on the other hand, it prevents the end user from disassembling it to avoid injury. The sight that presented itself to me was unpleasantly surprising: the printed circuit board of the charger was partially covered with soot from a burnt resistor, one of the tracks on the printed circuit board had burned out. And what was most striking was the low quality of the circuit design; it resembled the cheapest Chinese chargers, the so-called “no name”.

Because Time was running out, I looked at the list of accessories on the NOKIA website and chose a new charger model, AC-5E, compatible with my phone. It attracted me with its exceptional compactness, which is important if you need to take the charger with you on a business trip or vacation. Then I went to the Euroset communication store nearest to me and purchased the above-mentioned charger there.

It was sold in original packaging with the NOKIA logo and looked exactly like the image on the company’s website. The Rostest certification logo was also present on the case. In the evening I returned home from work and put the phone on charge, 20 minutes later the story repeated itself. There was a click and a smell of burnt plastic. The charger has failed. I was already beginning to doubt whether everything was okay with the mobile phone, perhaps it was the cause of these fireworks? But I didn't pay attention to it. In the end, all devices are divided into two categories - those that have already failed, and those with which this is about to happen :). The next day I returned to the salon and replaced the failed charger with a new one. Then I put the phone on charge with the old (included) charger. Charging went as usual, I did not notice any anomalies. A few days later I set the phone to charge using the new AC-5E charger. The phone's battery was almost completely discharged; usually the charging process in this case takes about 50 minutes. An hour later I checked the phone and the charging process was still ongoing. At the same time, the charger itself became noticeably hot, which I did not observe when using the included AC-4E.

Because I wasn’t going to go out anywhere, so I decided not to turn off the phone and wait until it was fully charged. When the charging process is complete, the phone emits a short beep and the battery indicator stops at the top. This beep sounded 3.5 hours after I connected the phone to the charger.

Curiosity won out, and I took apart the new charger. The circuit design used in it reminded me most of all of the AC-4E charger that has sunk into oblivion and its supposed cheap Chinese analogues. I couldn’t stand it any longer and disassembled the AC-4E charger that came with my phone. I must say, on the one hand, what I saw made me happy - the quality of this device was very good, but on the other hand, it made me sad, because... this meant that all the chargers I purchased were most likely counterfeits.

Let's take a closer look at chargers.

Note: Currently, the function of charging a mobile phone battery is assigned to the phone itself and partly to the battery. In this connection, the charger is a conventional power supply with the input/output characteristics required in each specific case.

3. Original NOKIA AC-4E charger

Marking

Power connector

On the bottom of the case you can see the model name, characteristics, barcode and serial number of the device. All inscriptions are clearly applied; the plastic has a pleasant, rough-to-the-touch surface. The NOKIA logo can be seen on the inner surfaces of both parts of the case.

Printed circuit board, top view

Printed circuit board, bottom view

The single-sided printed circuit board is neatly made, all parts are present, and a voltage regulator is used (a small chip on the bottom side of the board). Both conventional and SMD components are used. The board is marked “Friwo”, this is the name of the company that produced these chargers for NOKIA.

Judging by the information on the website, this is a fairly large company specializing in the production of power supplies and chargers. In order to be able to compare the two “versions” of the AC-4E chargers I have, I took a close-up photograph of the charger case outside and inside, the markings on the case, the printed circuit board and the power connector. I will do the same for the remaining two devices.

4. Charger NOKIA AC-4E

Charger NOKIA AC-4E, general view

Marking

Inner surface of the top

Inner surface of the bottom

Power connector

As you can see, it is impossible to distinguish this charger from the previous one externally. The same coating, exactly the same connector, the same markings on the bottom of the case, barcode and number. Same screws with original head. In general, there is nothing to complain about. A slightly different impression emerges if you look inside. The lower part of the case is almost identical to the original charger. The top does not contain the NOKIA logo on the inside.

Printed circuit board, top view

Printed circuit board, bottom view

The printed circuit board is generally made neatly, but the circuit design is more primitive. SMD elements are not used, there is no manufacturer marking on the board. In fact, this is one of the simplest options for a switching power supply.

5. Charger NOKIA AC-5E

Charger NOKIA AC-5E, general view

Marking

Top cover

Power connector

Neat and compact case, exactly the same power cable as the original AC-4E, with a Velcro strap to secure the cable when folded. All inscriptions are clearly marked - model name, NOKIA logo, characteristics and barcode with number. Inside we see a board that is very reminiscent of the “budget” version of the AC-4E adapter. The same lack of manufacturer markings, the same primitive circuit design (however, in this case there are differences, which we will discuss below).

As for the lack of manufacturer's marking, this is extremely strange, because... On the body of the device you can see a small inscription ASTEC. This is the name of a large company that produces power supplies for many mobile phone manufacturers. ASTEC is part of the EMERSON group of companies.

6. Chargers from other manufacturers

In order to be able to compare ASTEC products with the existing NOKIA AC-5E charger, I disassembled two more original chargers I had, one of them was supplied with the Siemens C65 phone, and the second was included with the Motorola V3 RAZR phone.

Siemens charger printed circuit board, top view

Siemens charger printed circuit board, bottom view

The characteristics of the Siemens charger are 5 V, 350 mA.

Motorola charger circuit board, top view

Motorola charger circuit board, bottom view

The characteristics of the Motorola charger are 5 V, 550 mA.

Both of these devices are manufactured by ASTEC, as indicated by the markings both on the chargers themselves and on the printed circuit boards of the devices. As you can see, the boards are made very carefully; SMD elements are used. Manufacturer's markings are present.

7. Field tests

Let's return to the NOKIA AC-5E charger. The only reason why charging a phone using it could take so long was the discrepancy with the declared characteristics, namely low current. It is indicated on the body of the device that it provides a current of 800 mA at a voltage of 5 V. Let's check with a multimeter how much current the phone consumes during charging when using the original AC-4E charger and this AC-5E.

First, let's measure the voltage in the network, as you can see, it corresponds to the standards - 225 V.

We measure the voltage in the network

For reference: on the ASTEC website you can view the specifications of chargers of a similar group; they ensure compliance with the specified characteristics at a network voltage in the range from 85 to 265 volts.

Let's measure the current consumption when using the original NOKIA AC-4E charger. As you can see, the current consumption is 910 mA.

The characteristics stated for this device are 890 mA. The charger works stably and does not heat up, which means there is still some current reserve.

Now let’s measure the current consumption when using the “budget” version of the NOKIA AC-5E charger. As you can see, the current consumption is 330 mA.

Testing a fake AC-5E charger

In this case, the device gets quite hot during operation. This means it works to the maximum of its capabilities. Which is not surprising, given the primitive circuit design and ratings of the parts used. Hence the time it takes to fully charge the phone has increased significantly.

8. Original NOKIA AC-4E / AC-5E chargers

In order to dot all the i's, I decided to order two more NOKIA chargers, models AC-4E and AC-5E from the ULTRA Electronics online store. Let's start with the NOKIA AC-5E charger, because I have not yet seen its original version.

Because It’s impossible to distinguish the original from the fake by external signs, so I immediately disassemble the charger.

Printed circuit board NOKIA AC-5E (original), top view

NOKIA AC-5E printed circuit board (original), bottom view

As you can see, the quality of the contents of this charger is very different from the “fake” one, for the better. The circuit elements occupy almost all the free space inside the charger body. The circuit design is quite “complex”; SMD elements are used. The board bears the manufacturer's marking "ASTEC". We can confidently say that this is an original product.

Original NOKIA AC-5E charger, general view

NOKIA AC-5E power connector (original)

Marking NOKIA AC-5E (original)

The appearance of the original charger, markings and power connector are all exactly copied in its counterfeit version.

Let's move on to the remaining NOKIA AC-4E charger.

NOKIA AC-4E printed circuit board (original), top view

NOKIA AC-4E printed circuit board (original), bottom view

The charger's printed circuit board bears the manufacturer's marking "Friwo". The circuit design differs from the original charger discussed earlier; it has been simplified. This is a common trend for almost all electronics manufacturers.

Charger NOKIA AC-4E, general view

Marking

Inner surface of the bottom

Power connector

The appearance of the charger has not changed.

Despite the fact that this Nokia AC-4E charger is undoubtedly original, the quality of the copy that came to me was unpleasantly disappointing. However, we will talk about this in the second part of “Field Tests”.

Appearance of the original packaging of Nokia AC-4E and AC-5E chargers

9. Field tests, part two

Let's test the two remaining chargers, the “updated” version of NOKIA AC-4E and NOKIA AC-5E.

On the AC-5E case it is indicated that the charger provides a current of 800 mA at a voltage of 5 V. Let's measure the current consumption.

Testing the original AC-5E charger

As you can see, it is equal to 880 mA. During operation, the device heats up slightly. In this case, the real characteristics of the device are even better than the declared ones. This charger can be recommended as a more compact replacement for the AC-4E model.

Unfortunately, testing the “updated” version of the AC-4E charger is not going so smoothly. Let's start with the fact that when connected to the phone, the charger began to emit a low-frequency hum, and the phone itself did not even think about charging. I took it apart and decided to check the output voltage directly at the PCB pins. It turned out to be 5.8 V, which is quite normal for operation without load. At this moment I noticed the charger cable; it consists of two wires insulated in black and white, respectively. However, a black wire, contrary to my expectations, was soldered to the “+” contact of the printed circuit board (as could be judged by the multimeter readings). It turned out that the wires were soldered incorrectly.

In this case, we are dealing with a defective product. Apparently, the quality of final product control at the FRIWO company has deteriorated.

After I soldered the wires properly, the phone began to respond to the connection of the charger, and it was possible to measure the current consumption during the charging process.

Testing the original AC-4E charger

The result is 400 mA with the stated 890. In general, it is pointless to interpret such a result, because the device was obviously defective and had to be replaced.

10. Conclusions

The findings are disappointing. Even if you buy an “original” charger from a well-known company, you are not immune from counterfeiting. In addition, the appearance of the device is copied so well that, even knowing about this problem, it is almost impossible to distinguish it from the original. Unless you come to the store with a multimeter.

And a little positive: as practical experience has shown, the phone itself, both in the case of using a counterfeit charger, and in the case of using a defective copy of the original charger with the wrong polarity, remained alive. Inconveniences are caused by: increased charging time, frequent cases of counterfeit chargers failing, and the fact that you had to pay for the counterfeit as if it were an original charger.

As a rule, repairing such an inexpensive device is not economically profitable.
Especially in non-poor countries. Average price 5 dollars.
But it happens that there is no extra money, but there is time and spare parts.
There is no store nearby. Circumstances do not allow. Then it's not about price.

In my case, everything was simple - one of my two chargers broke Nokia AC-3E, friends brought a bag of broken chargers. Among them were a dozen branded Nokia chargers. It was a sin not to take it.

The search for the circuit did not lead to anything, so I took a similar one and converted it to the AC-3E. Many chargers for mobile phones are made using a similar scheme. As a rule, the difference is insignificant. Sometimes the denominations are changed, a little more or a little less elements, sometimes a charge indication is added. But basically the same thing.
Therefore, this description and diagram will be useful for repairing not only the AC-3E.

The repair instructions are simple and written for non-specialists.
The scheme is clickable and of good quality.

THEORY.

The device is a blocking oscillator operating in a self-oscillating mode. It is powered by a half-wave rectifier (D1, C1) with a voltage of approximately +300 V. Resistor R1, R2 limits the starting current of the device and acts as a fuse. The blocking oscillator is based on a transistor MJE13005 and a pulse transformer. A necessary element of the blocking generator is a positive feedback circuit formed by winding 2 of the transformer, elements R5, R4 C2.

The 5v6 zener diode limits the voltage at the base of the MJE13005 transistor to within five volts.

Damper circuit D3, C4, R6 limits voltage surges on winding 1 of the transformer. At the moment the transistor is turned off, these surges can exceed the supply voltage several times, so the minimum permissible voltage of capacitor C4 and diode D3 must be at least 1 kV.

PRACTICE.

1. Disassembly. The screws holding the charger cover in this device have the shape of a triangular star. As a rule, there is no special screwdriver at hand, so you have to get out as best you can. I unscrewed it with a screwdriver, which, over the course of its use, had become sharpened into all sorts of crosses.

Sometimes chargers are assembled without bolts. In this case, the body halves are glued together. This indicates the low cost and quality of the device. Disassembling such a memory is a little more difficult. You need to split the body with a non-sharp screwdriver, gently pressing on the joint of the halves.

2. External inspection of the board. More than 50% of defects can be detected precisely through external inspection. Burnt resistors and a darkened board will show you the location of the defect. A burst case or cracks on the board will indicate that the device was dropped. Chargers are used in extreme conditions, so falls from anywhere are a common cause of failure.

In five out of ten memory systems that I had the opportunity to do, they were trivial contacts bent through which 220 volts are supplied to the board.

To fix it, just slightly bend the contacts towards the board.
You can check whether the contacts are at fault or not by soldering the power cord to the board and measuring the voltage at the output - the red and black wires.

3. Broken cord at the output of the charger. It usually breaks at the plug itself or at the base of the charger. Especially for those who like to talk while charging the phone.
Called the device. Insert the lead of a thin part into the center of the connector and measure the resistance of the wires.

4. Transistor + resistors. If there is no visible damage, first of all you need to unsolder the transistor and ring it. It must be borne in mind that the transistor
MJE13005 the base is on the right, but it also happens the other way around. The transistor may be of a different type, in a different housing. Let's say MJE13001 looks like a Soviet KT209 with the base on the left.

Instead I installed MJE13003. You can install a transistor from any burnt-out lamp - a housekeeper. In them, as a rule, the filament of the bulb itself burns out, but the two high-voltage transistors remain intact.

5. Consequences of overvoltage. In the simplest case, they are expressed in a short-circuited diode D1 and a broken resistor R1. In more complex cases, the MJE13005 transistor burns out and inflates capacitor C1. All this simply changes to the same or similar details.

In the last two cases, in addition to replacing the burnt conductors, you will need to check the resistors around the transistor. With the diagram this will be easy to do.

Very often I come across repairs to “not charging” phones. Nokia. I would like to immediately note that with the increase in the model range and the improvement of charging circuits, their reliability has decreased by an order of magnitude. Who in their practice has not encountered the problem of how to understand whether the phone is charging or not?
Of course, this can be checked by increasing the voltage on the battery itself, but this method is quite slow and it is not always possible to get to the battery contacts. You can look at the running charging icon on your phone and wait for the long-awaited message to appear. "Charging complete" or constantly remove the battery and measure whether the treasured millivolts have appeared in it...

Personally, I mainly control charging based on the current consumed from the charger. For this I have cords from burnt "Chinese chargers", I’m sure that every master has plenty of them, which I connect to laboratory power supply with adjustable voltage and current. For phones Nokia I set the charging voltage 5.7V and the charging current is from 600 mA before 1100 mA. Don’t forget that in modern phones of this brand, the charging current limit is controlled by the phone, but in previous models this task was performed by both the phone and the charger itself. I think that you have encountered such a problem before, when the phone completely refused to charge "Chinese charger" devices and everything was fine with the original one.

After all, it’s no secret that stable voltage and correct charging current for each specific battery are the key to long-term and trouble-free operation of the phone. But unfortunately, not everyone understands this, especially the “woe of the master” who completely throw out the whole purpose of charging and current control, and bypass it by placing a jumper with a diode directly from the charger to the battery terminals. REMEMBER THISDO IT IS FORBIDDEN!

I would like to make the troubleshooting process a little easier by constructing a small algorithm:

When you receive a phone that is not charging, check the integrity of the contacts of the charging and system connectors, depending on where the charger is connected.
Make sure that the battery is in good condition, that the terminals are making good contact and that they are not dirty.
Measure the charging voltage for phones Nokia this is about 5.7 volts.
Check the integrity of the soldering of system and charging connectors, very often new connectors "fall off" cracks appear in places where they are soldered, firstly from use lead-free soldering, secondly, from an unfinished fastening and thirdly from a careless attitude towards the phone itself, this is usually a rough connection and disconnection of the charger connector.
Now let's move on to messages that the phone gives when connecting the charger:
- "Not charging"— as a rule, there is a problem with the temperature sensor; the charging controller cannot determine the temperature of the battery and prevents it from overheating. As a rule, this is a thermistor with a resistance of 47 kOhm and is located close to the battery.
- "Charger not supported"- the problem is associated with a deviation in the voltage coming from the charger, and can be caused by a “sag” of voltage on passive elements - capacitors, protective zener diodes and varistors.
But it happens that everything is correct and the phone does not respond at all to connecting the charger, the simplest reason for this could be a blown fuse in the charging circuit, but do not forget that it could have burned out not only due to the fault of the external power source, but also due to an internal malfunction of the charging controller or the battery itself.
There are times when everything seems to be fine, the phone display does not give out non-standard messages, but something is wrong, the voltage on the battery does not increase and consumption from the current source does not occur. This may be due to a faulty current sensor, which in most phones is installed on the board and on some models is made in the form of printed conductors in the internal layers of the board. Structurally - a resistor with a small transition resistance of tens milliohms connected to the negative (minus) terminal of the battery and installed as close as possible to the battery connector.
Very often the problem lies in a faulty charging controller, it can only be checked by replacing it with a known good one.
There are also cases of software errors when, after various types of erases and overwrites, an area in the phone’s memory is erased P.M. in which voltage calibrations are stored. You can also check this by reading detailed information about the connected phone using the good old UFS or any other type programmer MX-key, JAF, Best, Fenix and so on.

Of course, this is not a complete list of what you might encounter when troubleshooting, but following this algorithm will save you a lot of time during repairs. If you have your own experience in the field of troubleshooting charging problems in phones Nokia I will be happy to supplement the article and publish your methods and techniques, for this