The switching power supply is the heart of the frequency converter , responsible for supplying power to all other components. Therefore, its normal oscillation is the primary condition for dynamic maintenance of the frequency converter. For more information on industrial circuit boards, elevator circuit boards, and frequency converters, please follow "Frequency Converter Repair from Zero".
The key to a switching power supply is whether it can oscillate normally at the oscillation point. This oscillation point refers to the lowest PN voltage (230VDC) required for the ICBoard driver board of the MOSFET to operate normally.
Test method: Remove the fuse in the upper left corner of the motherboard and connect a simulated load resistor board (this board can be made by adding a few resistors to the power output terminals of the motherboard, such as a 2K/1W resistor between 24V and COM, a 1K/1W resistor between +5V and GND, and an LED connected in series to serve as a power indicator). See Figure 8.4.1 for the power-on method.
Apply a voltage regulator to the switching power supply input P and common negative terminal N to approximately 230VDC, and observe whether the power indicator light on the analog load board lights up.
A load is required for a switching power supply to function properly, but a CPU board cannot be directly connected for testing. The purpose of adding a simulated load is to prevent the CPU from burning out due to excessively high power supply voltage, or to prevent the switching power supply from failing to oscillate due to a faulty CPU board.
The KVF+415GR switching power supply is designed to start at 230VDC. In actual operation, there will be deviations, but not exceeding ±30VDC. Exceeding this range will damage the power supply and other components over time. The circuit schematic for this part is shown in Figure 1.
Figure 1 Schematic diagram of switching power supply circuit
Table 2 shows the components that failed in previous statistics for switching power supplies.
Figure 2. Statistics of Easily Damaged Components in Switching Power Supplies
For static in-circuit maintenance of each component, please refer to the relevant content in Chapter 7, Section 2; for dynamic maintenance of ICBoard, please refer to the next section of this chapter.
If the circuit still fails to oscillate after replacing most of the components in Table 2, please consider whether the connection between the equipotential points on the printed circuit board is continuous. Use a multimeter in diode mode to measure whether there is a connection between any two equipotential points, as shown in points A, B, C, and D in Figure 1.
Is the power supply amplitude in Figure 3 normal?
Table 3: Overview of Amplitude Ranges for Various Power Sources
Note: + 3.3V is on the CPU board; see Section 3 of this chapter for details.
In past statistics, a common issue is that the power supply amplitudes are too high. If ±15V → 17V, +24V → +27V, and the resistance values of R5 and R8 are normal, the IC Board can be repaired or replaced (see the next section of this chapter for details). An inaccurate +5 value is likely due to a problem with its Zener diode, LM2940. Statistically, this component is not easily damaged. For more information on industrial circuit boards, elevator circuit boards, and frequency converters, please follow "Frequency Converter Repair from Zero".
Schematic diagram of each output power supply circuit of the frequency converter
