Testing and maintenance of switching power supply transformers

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Testing and maintenance of switching power supply transformers [Copy link]

Most color TVs use switching power supply circuits because switching power supplies have the characteristics of high efficiency and low power consumption, and the switching power supply transformer is the main component of the switching power supply.

1. Testing method of switching power supply transformer

(1) Appearance inspection. The operating frequency of the switching power transformer is relatively high, at 15625Hz. Generally, magnetic materials are used to conduct magnetism. Common faults are leakage or short circuit between windings, which makes the TV set have no raster or sound. When inspecting, you should first observe the appearance to see if there are traces of burning, whether the appearance is too dirty, and whether there is dirt between the pins (some switching power transformers have very small spacing between the pins, such as the Sanyo 83P movement switching power transformer). Since the switching power transformer is installed close to the printed circuit board, it is easy to accumulate dust and discharge and spark when the climate or environment is humid.

(2) Multimeter test. If there is no problem with the appearance of the switching power supply transformer, you can use a multimeter to measure its resistance value to determine whether the coil has a short circuit fault. The multimeter can also be used to measure the switching power supply transformer with a more serious short circuit. When measuring, you can select an appropriate resistance range so that the measured resistance value is near the median value. According to the number of turns of the winding and the wire diameter used, find out the ohm value per meter of the enameled wire, calculate the ohm value of the winding, and compare it with the measured resistance value to determine whether there is a short circuit. However, this is only a rough measurement. Some switching power supply transformers have insulation breakdown between turns or insulation breakdown between layers, and the resistance values are not much different, so they may not be measured.

The insulation resistance between the windings of the switching power supply transformer is infinite, and the insulation resistance between the windings and the magnetic core (iron core) should also be infinite.

(3) Substitution test. If you have a switching power supply transformer of the same specification, you can use substitution test, which is intuitive and convenient.

(1) Discharge and sparking. Discharge and sparking observed on the outside are usually caused by dirt on the pins of the switching power transformer and insulation damage. Repair method: Remove the switching power transformer and use anhydrous alcohol and medical cotton balls to thoroughly clean the pins, outer surface, and printed circuit board of the switching power transformer. If insulation damage is found, wrap the damaged part with polyester tape.

(2) Coil is broken. When a switching power supply transformer is found to have a circuit breaker fault, you should first check whether the broken wire is near the transformer pin (which is prone to false welding of the wire ends). Use tweezers to fiddle with the lead wires to quickly find the fault point.

(3) The core is broken. If the core is broken, it can be glued firmly with adhesive before use. It will not have any adverse effect on the TV. (4) The coil is short-circuited. Find out which coil is short-circuited, then fold the coil (remember the number of turns, position, winding direction, and pins) and rewind it.