Practical information | Disassembly and analysis of the internal circuit of the visual air fryer

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‍With the rise of healthy eating, air fryers that claim to be able to fry chicken nuggets, French fries and bake with just one click without using oil have become small appliances favored by foodies. A few years ago, a friend bought a Liven second-generation air fryer (LR-KZ880 model, light wave heating tube, 10-liter large volume). It is said that it is rarely used in normal times. Recently, it has a malfunction and the buttons on the control panel do not work when pressed. The maintenance staff told me that the circuit board is broken and it will cost hundreds of yuan. My friend didn't want to send it to the store for repair, and it would be a pity to throw it away, so he asked me to help take a look and see if it can be used as a last resort. If it is difficult to repair, just throw it away.

Generally speaking, an oven uses the radiant heat emitted by electric heating elements to bake food. According to the different needs of baked food, the temperature of the electric oven can generally be adjusted within the range of 50-250℃. It can be used to make roast chicken, roast duck, and bake bread.

The air fryer is essentially an oven, but it has an additional fan. Its working principle is to use the fan to blow heat to the food and use the hot air generated by air circulation to separate the fat from the food, making the food taste closer to fried food.

So, to put it simply, the air fryer borrows the hot air function of a high-end oven to allow the oven to make more delicious food.

1. Appearance

It seems that it has not been used many times and is in very new condition:

After power on, there is a display, but pressing the buttons on the control panel does not respond, a bit like a "downtime":

On the back of the machine, there is a power socket:

Nameplate indication: 220V, 1200W, 10L capacity, model LR-KZ880, light wave tube heat source.

At the bottom, there are six silicone pads to prevent sliding when placed on the countertop:

Pull the handle of the flap upwards to open the transparent cover and put the food in to bake:

Take out the double-layer non-stick pan (the outer layer is heat-resistant plastic, and the inner layer is a Teflon-coated metal basin, also known as an oil dripping bucket, which collects the oil dripping from the baked food):

On the column, there is a hole for the shaft that drives the grill to rotate. On the base, there is a micro switch that detects whether the pot (oil dripping bucket) is in place:

Inside the transparent cover (flip), on top, there is a heating system:

2. Disassembly and structure

Hold the transparent cover (if it is tight, it is recommended to use both hands) and carefully rotate it counterclockwise to remove it:

The structure of the heating system: there is a metal protective mesh cover on the outside and light wave heating tubes and fans on the inside.

Remove the one fixing screw at the bottom of the metal protective screen:

Remove the protective net:

Inside is a circular light wave heating tube and a metal fan impeller. Since this fryer is a closed type, the oil smoke will be deposited on the inner wall and the lamp tube:

This is a 1200W light wave tube, which is actually a ring-shaped halogen lamp:

Between the light wave tube leads is a metal-sheathed negative temperature coefficient resistor (room temperature 27°C, resistance 93.8KΩ), which serves as a temperature sensor:

Now that it's been taken apart, let's clean it up. First, use a strong kitchen grease cleaner to scrub it:

Then wipe it clean with a rag:

Much cleaner:

Remove the three screws holding the heater's metal cover in place and remove the cover:

After removing the outer cover, we can see that there is an insulating space behind the aluminum plate of the heater:

From this perspective, a coaxial fan impeller is installed in the heat-insulating space to blow out the heat to prevent the flip handle from getting hot, and at the same time, it also plays a role in airflow cooling for the circuit board in the flip handle:

Remove the eight screws that hold the flap handle in place:

Remove the circular cover from the shaft:

Then remove the fixing screws at both ends:

After removing all the fixing screws, you can separate the flap handle and see the internal circuit board:

The control circuit board installed on the upper cover of the flip handle:

The fan motor and main circuit board installed in the flip handle:

Micro switch at the shaft (the contact opens or closes when the flip handle is opened or closed):

Remove the cover on the back of the column, and the claw-pole permanent magnet synchronous motor inside is the drive for the grill to rotate:

There is a photoelectric switch on the motor shaft, and its signal is used to control the grill to rotate continuously or on one side:

Remove the 4 fixing screws of the base cover:

See there is a micro switch inside:

This micro switch is used to detect the placement of the non-stick pan (oil drip bucket):

3. Circuit components

The fan motor adopts a single-phase shaded-pole motor, 220V, 4W, and a speed of 2200r/min

Next to the fan motor, there is a temperature fuse fixed on the iron plate. When the circuit has a temperature control failure, it plays the role of finally cutting off the circuit. This temperature fuse is narrow and difficult to replace, and the temperature value is unknown:

Remove the screws that fix the main circuit board and take out the main circuit board:

Distribution of component functional areas on the main circuit board:

On the circuit board, RX1 is a 10Ω 2W fuse resistor, the blue disc RV1 is a varistor, and the yellow MC1 is a safety capacitor:

IC3 is a non-isolated power management chip PN8123 commonly used in small household appliances:

IC4 is 78L05, a three-terminal linear regulator, which provides 5V regulated power supply for the microcontroller:

IC2 is a commonly used single-chip microcomputer in household appliances, model S3F9454BZZ-DK94. The yellow component CY1 below is a three-pin 8MHz ceramic filter. IC1 is a high-current drive array integrated circuit ULN2003AN, which is mostly used in control circuits such as single-chip microcomputers, intelligent instruments, PLCs, and digital output cards. The output can reach 500mA/50V and can directly drive loads such as relays. The black cylinder BUZ next to it is a buzzer.

12V DC relay, model JQC-3FF, contact load 10A 277VAC, is responsible for cutting off or connecting the power supply of the light wave heating tube, fan, and grill rotating motor when the flip cover handle is opened or closed:

The following is a bidirectional thyristor that drives a 1200W light wave heating tube, model BTA16-600B (16A/600V). Due to the large working current and high heat generation, the aluminum heat sink is relatively large:

Next to the radiator, there are two low-power bidirectional thyristors, model BT31 (1A/600V), which are the drivers of the fan and grill rotation motors:

Control circuit board removed from the handle:

IC1 on the circuit board is the LED digital tube drive control integrated circuit, model CT1642:

There are three LEDs (L1, L9, L12) on the circuit board driven by Q1 (9014), and the remaining LEDs are driven by CT1642:

4. Circuit working principle and circuit diagram

1. Circuit principle

According to the circuit board, the circuit principle block diagram of the air fryer is drawn as follows:

Circuit working principle:

Plug in the power supply. Only when the oil dripping bucket (pan) is placed in the correct position and its micro switch K is turned on, the 12V switching power supply and the 5V regulated power supply can work and the control system is powered on. The program self-checks. When the temperature and the position of the flip handle are normal, the buzzer emits a long "beep", the relay J is turned on, and the digital tube displays "000", preparing to start the machine. Then, set the baking program on the control panel, press the "Start" button, and the machine starts working. During baking, when the temperature reaches the set value, the single-chip microcomputer will issue a command to stop the light wave tube heating; when the temperature is lower than the set value, the single-chip microcomputer will issue a light wave tube heating command, and it will continue to alternate until the time is up. In the middle of baking, if you want to open the flip cover and brush oil on the baked food, you can directly lift the flip cover handle, the micro switch at the handle shaft is disconnected, and the single-chip microcomputer receives the disconnection signal and issues a disconnection relay command. The light wave heating tube, fan, and grill rotating motor will stop running immediately. When the flip cover is restored, the original program is restored to continue baking. In the circuit, the digital tube displays the time, the red LED displays the set baking mode, and the green LED is the working indicator. When the temperature fuse exceeds the maximum limit or a serious short circuit occurs, the power supply of the whole machine is cut off, and the machine can resume normal operation only after the fault is eliminated and a new temperature fuse is replaced.

2. Circuit diagram

Comparing with the actual object, the circuit diagram is drawn as follows. They are the main circuit board circuit diagram and the control board circuit diagram. The parameters of each component are marked on the circuit diagram. There may be imperfections, which are only for reference when you repair.

⑴The circuit diagram of the main board is as follows:

⑵The control board circuit diagram is as follows:

5. Troubleshooting the unresponsive control panel

1. Fault cause analysis and inspection

The panel button functions are shown in the figure below:

Analyze with the circuit diagram. Under normal circumstances, the machine is powered on and passes the self-test. Only by pressing the "Function" key, selecting the baking program, and then pressing the "Start" key, can the machine start working. If the panel buttons do not respond, first check whether there is a problem with the "Function" key!

On the control circuit board, the micro switch number of the "Function" key is K6. Use the resistance range of the multimeter to test it. If it does not work when pressed, there is a problem! The other micro switches are fine:

2. Repair faulty components

Drip anhydrous alcohol into the gap of K6 microswitch and press the key repeatedly (the circuit board must be erected to allow the liquid inside the microswitch to flow downward) to clean the contact surface inside the microswitch:

After the alcohol evaporates, use a meter to test it, press it, and it works! To be on the safe side, handle the other micro switches as well.

Reinstall the machine, power on and test the machine. The panel buttons respond and the fault is eliminated:

After setting the baking mode, press the "Start" button and the machine will work normally. However, the light is quite strong and looks a bit dazzling:

VI. Conclusion

1. The essence of an air fryer is an electric oven with internal hot air circulation. The oil inside the food is forced out by heating and baking (some foods must be brushed with oil separately), making the food crispy on the outside and tender on the inside. You need to fully master the characteristics of the machine and food processing skills to make delicious food. Practice makes perfect, just practice more. Although the heating of light wave tubes is intuitive, I personally think that light loss and light pollution are also a problem.

2. Micro-switch failure is a common problem for this type of small household appliances. This is mainly because domestic manufacturers, facing fierce market competition, do not hesitate to lower the quality control standards in order to control production costs, resulting in unsustainable products. When repairing, you can go straight to the key electronic components and replace them after inspection.

Source: Digital Home Author: goodanytime Copyright belongs to the author

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