How to use a multimeter to measure the quality of a ballast
A multimeter can only measure the quality of an inductive ballast. If the resistance level of the multimeter is tested, it is generally considered normal. Set the multimeter to the ohm range and use two probes to test the wiring terminals of the ballast. If there is a certain resistance value, it is good. The size of the resistor is related to the power of the fluorescent lamp. For example, a normal 40W ballast has a resistance of about 50 to 60 Ω. If the inductor is broken, the resistance may not be the same, it may be very large or very small, especially for inter turn short circuits, which are difficult to judge, so it can only be roughly referenced
If it is an electronic ballast, it cannot be measured carefully with a multimeter without disassembling it. Without disassembling, measure the resistance of the four wires connected to the lamp tube with a multimeter. There should be no bidirectional conduction between any two wires, otherwise the internal resonant capacitor will break down, indicating that the ballast is damaged. In other cases, measure each component one by one.
Another method is to use a multimeter to measure the pins of two transistors in an electronic ballast without a lamp when it is charged. The middle pin of one transistor is about 300 volts to ground (negative), while the middle pin of the other transistor is about 90 volts to ground. If such data is obtained, it indicates that the electronic ballast is basically good. Of course, safety should be taken into account during live measurement to avoid short circuits. Then, when there is no electricity or light tube, measure the four lead wires from the electronic ballast to the light tube end, with any row number of 1, 2, 3, and 4 lead wires. There should be no short circuit between 1 pair of 2, 3, and 4, and no short circuit between 2 pairs of 1, 3, and 4 (i.e. zero resistance). If there is a short circuit, you can follow the short-circuit line to check. If one of the capacitors is damaged, replace the damaged capacitor and it will be repaired. The electronic ballast outputs high-frequency electricity, which is difficult to check with a multimeter. If conditions permit, use an oscilloscope to measure.
A 40W incandescent bulb and ballast can be connected in series to the power supply. A good ballast will dim the light but will not go out. Electricians usually replace light tubes and ballasts, and the replacement method is actually the quickest way to repair these things.
