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1. Detection of Color Code Inductors

Place the multimeter in R

× At first gear, connect the red and black pens to either end of the color code inductor, and the pointer should swing to the right. According to the measured resistance value, there are three specific situations for identification:

1. The resistance value of the tested color code inductor is zero, and there is a short-circuit fault inside it 2. The DC resistance value of the tested color code inductor is directly related to the diameter of the enameled wire used for winding the inductor coil and the number of windings. As long as the resistance value can be measured, the tested color code inductor can be considered normal

2. Detection of mid cycle transformers

1. Set the multimeter to R

× First gear, check the on/off status of each winding one by one according to the pin arrangement pattern of each winding of the mid cycle transformer, and then determine whether it is normal 2. Check the insulation performance and set the multimeter to R × 10k gear, perform the following state tests:

(1) Resistance value between the primary winding and the secondary winding (2) The resistance value between the primary winding and the casing (3) The resistance value between the secondary winding and the casing The above test results can be divided into three situations:

(1) The resistance value is infinite: normal (2) Zero resistance value: there is a short-circuit fault

(3) Resistance value less than infinity but greater than zero: there is a leakage fault

3. Detection of power transformers

1. Check for obvious abnormalities by observing the appearance of the transformer.

If the coil lead wire is broken, desoldered, the insulation material has burnt marks, the iron core fastening screw is loose, the silicon steel sheet is rusted, and the winding coil is exposed. 2. Insulation performance test Use a multimeter R × Measure the resistance values between the iron core and primary, primary and secondary, iron core and secondary, electrostatic shielding layer and secondary, and secondary windings at 10k gear. The multimeter pointer should be fixed at infinity. Otherwise, it indicates poor insulation performance of the transformer 3. Detection of coil on/off Place the multimeter in R × In gear 1, during the test, if the resistance value of a certain winding is infinite, it indicates that there is an open circuit fault in the winding 4. Distinguish between primary and secondary coils The primary and secondary pins of the power transformer are generally led out from both sides, and the primary winding is often marked with the word 220V, while the secondary winding is marked with the rated voltage value, such as 15V, 24V, 35V, etc. Then identify based on these markings

4. Detection of no-load current

Direct measurement method.

Open all secondary windings, Place the multimeter in the AC current range 500mA, connected in series to the primary winding. When the plug of the primary winding is inserted into a 220V AC mains supply, the multimeter indicates the no-load current value. This value should not be greater than 10% to 20% of the transformer's full load current. Generally, the normal no-load current of a common electronic equipment power transformer should be around 100mA. If it exceeds too much, it indicates a short-circuit fault in the transformer.

Indirect measurement method.

Connect one in series in the primary winding of the transformer A resistance of 10 Ω/5W, with all secondary circuits still empty. Set the multimeter to AC voltage. After powering on, use two probes to measure the voltage drop U at both ends of the resistance R, and then use Ohm's law to calculate the no-load current I empty, that is, I empty=U/R Detection of no-load voltage Connect the primary of the power transformer to a 220V mains supply, and use a multimeter to measure the no-load voltage values (U21, U22, U23, U24) of each winding in sequence. The required values should be met, and the allowable error range is generally: high-voltage winding ≤ ± 10%, low-voltage winding ≤ ± 5%, and the voltage difference between two sets of symmetrical windings with central tap should be ≤ ± 2%