Omron PLC switching power supply maintenance

If an Omron PLC does not display after power on, it is often because the switching power supply is broken. Don’t think it is so difficult to repair, so it is a pity to reimburse this PLC. The switching power supply of Omron PLC is often very simple. The circuit I surveyed and mapped according to the actual object is as follows:

This circuit is simply too compact. Except for a power module, there seems to be no other components. Recently repaired a few. It was found that this type of power supply has a “common problem”: there are only three bad components, the F11 fuse; the IC11 power module; the third component is the least noticed, that is, the electrolytic capacitor C12. In fact, it is also the “culprit” of the entire power supply damage. But to say it is the culprit is a bit unfair, listen to me.
C12 is installed close to the heat sink of the power module. After a long time, the electrolyte inside it will evaporate due to heat and gradually dry up. But C12 does not look abnormal on the surface, and the online measurement is not short-circuited. If it is removed, only a few microfarads are left to measure its capacity, which is one-tenth of the original capacity. The power module used to draw a steady current, but after the capacitor lost capacity, the loop current fluctuated somewhat. This time the power module can’t stand it anymore, and the breakdown and short circuit are logical. Of course, F11 also obeys the king’s order, and it’s over together. The loss of capacity of C12 exposes the unreasonable structural layout of the power supply – the electrolytic capacitor cannot be installed close to the heat sink. This is of course an oversight by the designers. Therefore, for Omron PLCs that have been used for more than a few years, when there is a phenomenon that it seems that there is no power when it is powered on, it is mostly because C12 has lost capacity, and due to the loss of C12, the IC11 module and F11 have “died”.
The damage of IC11 and F11 can be detected by using a test pen, and C12 is sometimes ignored. After replacing with a good part, it may be ok without loading when you turn on the power, but when you hear a “snap” when it is loaded, the good part you replaced is broken again. Don’t complain that the supplier provides you with defective products, but that your maintenance skills are not in place.
Be sure to check out C12! !

The circuit is simple and simple, you still want to understand the ins and outs of IC11——MIP0223SC power module—how the circuit works. If you can’t understand this, the circuit is really simple and boring. Let’s look at the IC11 schematic data sheet (it’s in English again, no way, it’s hard to find in Chinese):


In fact, foreign language information is not a big deal. It is not necessary to guess all the parameters, and it is not necessary to thoroughly understand each unit circuit in the schematic block diagram. For the block diagram, knowing the function of each pin of the component and what is connected inside the pin is enough. At least know how to start in the measurement, if you can detect a short circuit or an open circuit, you will be hit. For the data sheet, it is enough to only look at three or five key parameters. Such as the module’s power supply voltage, oscillation frequency, operating current, power capacity, signal drive current and voltage, that’s all. If you don’t understand, you can guess it!
Well, the principle of the circuit should be pondered slowly when you are free. Given the circuit diagram and module information, it is not enough for maintenance.

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