The electric car's headlights are not on, the horn is ringing, and there is a 60V voltage in one of the two control circuits of the headlight circuit board. Please help analyze it.

深圳小花

The electric car's headlights are not on, the horn is ringing, and there is a 60V voltage in one of the two control circuits of the headlight circuit board. Please help analyze it. [Copy link]

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The electric car's headlights are not on, but the horn is ringing. There is a 60V voltage at one of the two control circuits on the headlight circuit board, and the normal state of the circuit is 0V at two points. When the headlight is turned on, the voltage is 60V.

LED type I used a multimeter with the diode range to measure multiple LED lights in both positive and negative directions, but none of them were lit, and all displayed 1 (overflow). When one LED light was measured with the resistance range, it displayed 0.338M in one direction and 0.467M in the other direction.

Questions: (1) Why are there two power supply lines 1 and 2? (2) How do I use a multimeter to test the quality of an LED light? (3) How do I repair this circuit?

maychang

(1) Why are there two power supply lines 1 and 2?

Now that both sides of the circuit board have been posted, you can find out by carefully looking at which lights the red and black wires power and which lights the green and white wires power.

maychang

(2) How to test the quality of LED lights with a multimeter

LEDs, especially blue and white LEDs, cannot be measured with a multimeter diode function because blue LEDs require more than 3V to conduct.

深圳小花

maychang published on 2021-7-25 10:49 (2) How to test the quality of LED lights with a multimeter, especially blue and white LEDs, which cannot be measured with the diode range of a multimeter. Because blue...

Thank you very much. Isn't the battery used in the multimeter a 9V square battery? 9V should be able to drive a 3V LED blue/white light, right?

maychang

Shenzhen Xiaohua posted on 2021-7-25 13:12 Thank you very much. Isn't the battery used in the multimeter a 9V square battery? 9V should be able to drive a 3V LED blue/white light

Take a blue LED that is guaranteed to be intact, and use the diode function of your multimeter to test the forward and reverse directions to see if the LED is lighting up.

maychang

Shenzhen Xiaohua posted on 2021-7-25 13:12 Thank you very much. Isn't the battery used in the multimeter a 9V square battery? 9V should be able to drive a 3V LED blue/white light

Replacing suspected faulty components with known good components is a very common maintenance method.

chunyang

For the first question, you should draw a circuit diagram based on the PCB and components, and you should be able to understand it at a glance.

The second problem is that WLED cannot be directly measured with a conventional digital multimeter because the output voltage of the gear is insufficient. The battery in the meter does not directly power the external circuit, so the battery voltage has no direct relationship with the output voltage of the gear.

For the third question, first draw the circuit, fully understand the circuit principle, observe the solder joints of the circuit board and the appearance of the components, and eliminate obvious problems. Then connect a 60V power supply and use the voltage block to measure the voltage to ground at both ends of each LED and resistor from high potential to low potential. If the LED or resistor is damaged, the specific component can be analyzed and determined from the measured voltage. The knowledge used is only enough for the junior high school physics course.