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Common fault analysis and troubleshooting methods of the circuit board of the range hood!

Views : 1648
Author : elecontro
Update time : 2022-02-16 14:43:55

When the circuit board of the range hood is under the condition of normal input voltage, the system still cannot work, such as the key input does not respond, the work instruction is abnormal, the load does not work, etc., the priority should be given to whether the circuit board is working normally. The following is based on the characteristics of our products Analyze typical circuit schematics and analyze possible problems.

1. Power on and can't start

Fault analysis: This fault occurs mainly because the whole machine does not work when powered on, and the buttons and indicator lights do not respond. There are many circuits involved, mainly including the power circuit, the crystal oscillator circuit, and the reset circuit.
(1) Power circuit failure: check steps:
① Eliminate the problem of parts first, check whether the EMC protection, transformer, filter capacitor, fuse and power cord are damaged, replace the damaged parts, and troubleshoot.
② If the above steps do not find the problem, then we will power on the circuit to test (pay attention to the high-voltage power supply), first check whether there is 220V AC input, and then check whether the primary of the transformer has 220V AC voltage input.
Note: If the primary coil is damaged, generally the thermal fuse of the transformer is burned out. You can gently open the primary coil and short-circuit the fuse.
③ If there is no problem with the above high voltage power supply circuit. If it still cannot be turned on, it means that the fault is in the low-voltage power circuit. The low-voltage power supply circuit we refer to here refers to the 5V power supply circuit
(2), reset circuit failure: check steps:
Measure the voltage of pin 4 of the IC when the power is on. If the voltage is 0V, it means that the reset circuit is not working. Please check whether the corresponding capacitor is normal. If it is normal, it can be determined that the main control IC is broken. Replace the main control of the same type. IC, power-on test machine is normal, troubleshooting. If the voltage of pin 4 of the IC is measured to be 5V, and the fault is not eliminated, then we can also locate the fault on the main IC, and the fault can be eliminated after replacement.
Note: In this case, if replacing the resistor and capacitor cannot solve the problem, use the equivalent circuit board accessories instead.
(3) Failure of oscillation circuit: check steps:
Check the voltage to ground at both ends of the crystal oscillator or ceramic oscillator. Normally, it should be between 2 and 3V. If it is 0V or +5V, it means that the oscillation circuit is faulty. Replace it with a new crystal oscillator or ceramic oscillator of the same specification and test the machine. If it still cannot be turned on, only the main control IC is broken. Replace the main control IC of the same specification.
Note: In this case, if replacing the crystal oscillator or ceramic oscillator cannot solve the problem, use the equivalent circuit board accessories instead.
(4) Burning fuse: Failure analysis:
This fault usually occurs together with other parts damage, such as subsequent circuit short circuit, load short circuit, etc. After replacing the new fuse, do not immediately power on the test machine, otherwise it may cause the fuse to burn again.

   2.Low-voltage power supply circuit failure

   Fault analysis: This fault is generally caused by the failure of the components (voltage regulator module, regulator tube and auxiliary components) used in the voltage regulator circuit. Generally, after replacing the new components, it should work for a period of time to observe whether it is overheated. , if attention should be paid to it, it may be that other subsequent circuits are faulty.

   3.The load does not work

   Fault analysis: The fault is mainly due to the phenomenon that the motor and the lighting lamp do not work. There are many circuits involved, including the drive circuit and the load circuit.
(1), drive circuit failure: check steps:
① In the case of no load, if the startup is normal, use a multimeter to measure whether the voltage of the triode base is 5V. If the measured voltage is high, it means that the IC output is normal, otherwise it means that this port of the IC has been damaged.
② If the voltage measured in the previous step is normal, please use a multimeter to check the voltage of the collector of the triode. If it is below 0.7V, it means that the triode is working normally. Otherwise, it means that the triode is not conducting. The machine is normal, troubleshooting.
③ If the above two steps are normal, use a multimeter AC voltmeter to measure whether the voltage between the 7th and 8th points is within the mains range. If there is no output, it means that the relay is damaged. After the replacement, the test machine is normal, and the fault can be eliminated.
(2), load circuit failure: check steps:
① First check whether the load input voltage is normal. If it is not normal, check the interface to ensure that there is power input.
② For the motor and lighting, it can be judged whether it is working normally by observing the rotation of the motor or the lighting of the lighting. If there is no phenomenon, it means that the fault is on the load, and the fault can be eliminated after replacing the corresponding accessories.

   4.The buzzer does not sound

   Fault analysis: The occurrence of this fault indicates that there is a problem with the main control IC or the buzzer itself, so the fault range is located on the buzzer itself and the main control IC.

   5.The buttons on the display panel do not respond or the display is incomplete

Failure analysis: When the buttons on the panel do not respond or the display is incomplete, the problem may appear on the display board, the main control board and the connection line.
Diagnose the fault: In order to find the fault as soon as possible, we can divide the fault scope into the connecting line, the main control board and the display board. First, check for possible poor contact of the connecting line, which can be simply measured with a multimeter. After troubleshooting, replace the original display board with a good display board if possible. If everything is normal at this time, it means that the fault lies in the display board. If the above fault still exists, the fault has nothing to do with the display board, but the main control board is faulty.
Detection steps:
(1), the problem of the display board
① Disconnect the power supply, check whether there is any problem with the connection cable between the display board and the main board, and check whether the gap between the buttons on the display board and the buttons on the panel is too large or dead.
② Power on and check whether the power supply or signal on the display board is normal. If it is normal, you can use the resistance gear of the multimeter to carefully check whether all the components (buttons, LEDs, resistors) on the display board are faulty. If there is no problem with the above, the problem may be appears on the main control board.
③ If the main control IC is placed on the display panel, and touch detection is used, the possibility of the IC being damaged is very small. Therefore, the following items should be paid attention to when checking:
 A. Since the effective button requires the button medium (usually conductive spring or rubber) to be sensitive enough when the contact area between the button medium (usually conductive spring or rubber) and the panel of the whole machine is large enough, it should be carefully checked, including whether the screw is loose, the elasticity of the conductive spring and the contact area.
 B. Whether there is foreign matter in the button medium (usually conductive spring or rubber), such as water droplets, short circuit of conductive substances, etc.
  C. Whether the pads (especially those using springs) have virtual soldering or open circuit.
(2) Problems with the main control board
If the problem is the main control board, please check whether there is a problem with the chip port that interfaces with it. Since the buttons and display lights generally use the scanning mode, their levels change, and it can be preliminarily determined by whether the port voltage changes or not. If it is abnormal, it can only mean that the chip is damag
ed.

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