Disassembly of the power supply Xiaomi Redmi Note 9: tools, schemes and precautions

The Xiaomi Redmi Note 9 power supply is a compact but complex device that is more often replaced than repaired when it breaks, but in some cases (such as when the capacitors are suspected of malfunctioning, the fuse is burned out or damaged). USB-The disassembly connector can save the situation – especially if the original charger is no longer sold or its price is prohibitive. In this article, we will discuss in detail how to carefully open the power supply without damage, what tools will be needed for this, and what to pay attention to not to turn repairs into a dangerous experiment.

It is important to understand that even a charger turned off from the socket can store residual charge in the capacitors, which can cause electric shock. In addition, careless disassembly often leads to damage to the circuit board or to the break of thin wires. If you have never worked with electronics before, it is better to entrust the diagnosis to a specialist - especially if we are talking about fast-charging power units (Quick Charge 3.0), where the voltage at the output can exceed the standard 5V.

However, if you are considering a self-repair, follow our instructions Step-by-step.We have taken into account all the nuances of a particular Redmi Note 9 model (codenamed merlin), including the type of case, the mounting board and the location of critical elements.

1. Technical characteristics of the power supply Redmi Note 9

The charger, which comes with the Xiaomi Redmi Note 9, has the following options:

• 🔌 Type of connector: USB Type-C (reversible)
• ⚡ Power: 18 watts (Quick Charge 3.0)
• 📏 Sizes: 30 × 30 × 25 mm (may vary slightly)
• 🔋 Input voltage: 100–240 V, 50/60 Hz
• 📱 Exit voltage: 5V/3And, 9V/2And, 12V/1.5A (automatic definition)

The feature of this unit is the support of the Quick Charge 3.0 protocol, which means that there are additional elements on the board to adjust the voltage. MP2629 or similar), otherwise the device will no longer correctly determine the charging mode.

⚠️ Warning: If the power supply smells like a burn or the case is deformed, it is strictly forbidden to disassemble it! These are signs of an internal short circuit or fire - such devices are only subject to disposal.

2. Necessary tools and materials

To disassemble the power supply Redmi Note 9 you will need:

• 🔧 Flat screwdriver (preferably with a thin sting, 1-2 mm)
• 🔨 Plastic mediator (or guitar mediator) to disengage the body
• 🧲 Magnetic screwdriver (so as not to lose small screws)
• 🔍 loope USB-microscope (to inspect soldered compounds)
• 🧴 Isopropyl alcohol (90%+) clean-up
• 🔥 Dryer or soldering station (if soldering is planned)

Also, prepare your workspace: a table with good lighting, a rubber mat (to protect against static electricity), and a container for small parts. If you're going to test the board after disassembly, you'll need a multimeter with a diode check and resistance measurement mode.

Note that unlike older screw-mounted power supplies, the Redmi Note 9 is glued together using ultrasonic welding technology, which means that you just don't open it, you have to carefully tuck the seam around the perimeter. If you've never worked with such cases, practice on an unnecessary power supply (like an old phone).

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Before disassembling, take a photo of the power supply from all sides - this will help to properly assemble it back, especially if the screws or latches have different lengths.

3. Step-by-step disassembly instruction

Follow this algorithm to minimize the risk of damage to the fee:

1. Turn off the power supply and let it cool for 10-15 minutes, and even when it's off, the capacitors can store charge.
2. Take a plastic mediator and gently insert it into the seam between the top and bottom of the case. Start at the corner where it is. USB-jack - there welding is usually weaker.
3. Slowly drive the mediator along the seam, swaying it slightly from side to side. If the body does not respond, slightly heat the seam with a hair dryer (temperature not higher than 60).°C) to soften the glue.
4. Once the body opens, don't try to disconnect it right away. There may be latches or wires connecting the two halves. Check the inside for mounts.
5. If the board is fixed with screws, twist them out with a magnetic screwdriver and carefully remove the board, holding it by the edges. Don't touch the radio elements!

Unplugged and cooled.|Tools and workplace prepared|The appearance of the block is photographed|Wearing protective gloves (optional)|Integrity of the body (no cracks / bloating)-->

At this point, you'll see the internal design of the power supply.

• 🔋 Primary winding (network part, high voltage)
• 🔄 Transformer (reduces voltage)
• 📱 Secondary winding (USB-exit, low voltage)
• 🛡️ Protective elements (waristors, fuses, thermistors)

⚠️ Warning: If you notice bloated capacitors on the board (the top is convex or corrosion-covered), do not turn on the power supply.

Diagnosis of faults: what to look for inside?

After disassembly, check the fee for the following defects:

• 🔥 Blackened or burned areas - a sign of short circuit or overheating.
• 💥 Cracks on tracks – may occur due to mechanical stress (for example, a block falls).
• 🔋 Leaky capacitors – on their legs or near visible traces of electrolyte.
• 🔌 Oxygenated contacts - especially in the area USB-plug-in.
• 🧲 Folded elements – small resistors or diodes are often affected.

To check the integrity of the elements, use a multimeter:

• Safety: should show resistance close to 0 ohms. If "1" (break) - a replacement is required.
• Diodes: in one direction conduct current (squeaks multimeter), in the other – not.
• Capacitors: in the capacity test mode, the value must be consistent with the marking (e.g., 1000) µF ±20%).

If you find a defective element, you can solder it out and replace it with a similar one, which requires a 30-40 watt soldering iron and flux solder. Don't use acid flux, it will eventually erode the board tracks!

5.Typical breakdowns of the Redmi Note 9 power supply

Based on the analysis of service centers, the most frequent malfunctions of this power supply:

Especially often, users are faced with the problem of "unstable voltage" at the output, this manifests itself as a charging spike (it goes on and on) or a message on the phone "Charge suspended", the reason usually lies in faulty filter capacitors or damaged tracks near the center of the car. USB-plug.

If the power supply stopped turning on after the fall, but there is no visible damage, check the feedback circuit (feedback). In Redmi Note 9, it is implemented via an optron (usually marked with a marking). PC817), shatterable.

Assembly of the power supply after repair

After the fault is eliminated, collect the block in the reverse sequence:

1. Make sure that all the elements on the board are soldered tightly and there are no circuits between the tracks.
2. Check that the thermopaste is applied to the radiator (if any) and transformer.
3. Carefully put the charge in the case, making sure that the wires are not clamped.
4. Close the case and fix it with glue (for example, thermal glue or epoxy). Ultrasonic welding at home is not possible.
5. Allow the glue to dry (at least 1 hour) before first switching on.

Before the first use after repair:

1. Connect the unit to the network without loading (do not connect the phone!).
2. Check the body temperature in 5-10 minutes – it should not be heated above 40-45°C.
3. Measure the voltage at the exit with a multimeter.
4. Only then connect the phone for a full check.

⚠️ Warning: If after assembly, the power supply begins to buzz, spark or warm more than usual, immediately disconnect it from the network.

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After repair, the power supply loses its original dust moisture protection. Do not use it in high humidity conditions (for example, in the bathroom) - this can lead to a short circuit.

7.Repair alternatives: When is it easier to buy a new unit?

Repairing the power supply is not always justified.

• 💸 The cost of repair exceeds 50% of the price of the new unit.
• ⚡ Critical damage (burnt transformer, broken key transistors).
• ⏳ No time for diagnosis and ration.
• 🔧 No experience with high-voltage circuits.

The original power supply for the Redmi Note 9 can be found:

• In the official Xiaomi store (12-month warranty).
• On AliExpress (look for sellers with a rating above 98% and reviews of originality).
• In service centers, where used parts are sold with a guarantee.

When choosing an analogue, pay attention to:

• Power (must be at least 18 watts to support Quick Charge)
• Certification (there must be marks on the body) CE, RoHS).
• Type of connector (USB-C For the Redmi Note 9).

If you decide to buy a non-original unit, avoid "no-name" models without labeling. Cheap fakes often don't have overheating protection and can damage the phone's battery.

8. Safety measures when working with power supply units

Even low-voltage power supplies can be dangerous if handled carelessly.

• 🚫 Don't disassemble the grid unit, the risk of electric shock is up to 220V.
• 🧤 Use dielectric gloves when working with the board.
• 🔌 Discharge the capacitors before soldering (short the legs with a screwdriver with an insulated handle).
• 👓 Protect your eyes – when capacitors are bloated, electrolyte sprays are possible.
• 🚮 Dispose of defective blocks in special reception points (do not throw them into ordinary garbage!).

If you're not sure about your skills, you should go to a service center. Statistically, 70 percent of self-repairs of power supplies end in failure due to soldering or assembly errors. In the case of the Redmi Note 9, this is especially true, because the board has many small parts. SMD-Components that are easily damaged without experience.

Remember, saving on repairing the power supply can turn into a fire or a failure of the phone. If the unit warms, sparkles or smells of burns, do not take risks, replace it with a new one.

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Xiaomi's Quick Charge power units have a complex protection scheme.Improper repairs can turn off fast charging or cause the phone's battery to overheat.

FAQ: Frequent questions about the dismantling of the power supply Redmi Note 9