Common troubleshooting methods for power frequency converters
No display on keyboard after power on
1. Check if the input power supply is normal. If it is normal, measure whether the voltage at the P and N terminals of the DC bus is normal. If there is no voltage, cut off the power and check if the charging resistor is damaged or open.
2. After checking that the voltage at the P and N terminals is normal, the keyboard and keyboard cables can be replaced. If there is still no display, it is necessary to power off and check whether the 26P cable connecting the main control board and power board is loose or damaged or open circuit.
3. If the switch power supply works normally after power on, the relay makes a sound of suction, the fan operates normally, but there is still no display, it can be determined that the crystal oscillator or resonant capacitor of the keyboard is damaged. At this time, the keyboard can be replaced or repaired.
4. If everything else is normal after powering on, but there is still no display, the switch power supply may not be working. At this time, it is necessary to power off and unplug the P and N terminals to check whether the static state of IC3845 is normal (based on experience). If IC3845 is static and normal, the voltage at both ends of the 18V/1W voltage regulator diode is about 8V after applying DC voltage to P and N, but the switch power supply is not working. After power off, check if there is a breakdown or short circuit in the rectifier diode on the secondary side of the switch transformer.
5. After power on, there is voltage on the 18V/1W voltage regulator diode, but there is still no display. You can remove some peripheral plug wires, including relay wire plugs and fan wire plugs, and check if there is a short circuit in the fan and relay.
After powering on the P and N terminals, the voltage at both ends of the 18V/1W voltage regulator diode is about 8V. Use an oscilloscope to check whether there is a sawtooth wave on pin ④ of the input terminal of IC3845 and whether pin ⑥ of the output terminal has an output.
7. Check if there is a short circuit between the output terminals of the switch power supply+5V, ± 15V,+24V, and each drive power supply to ground and between poles.
The keyboard displays normally, but cannot be operated
If the keyboard displays normally, but all function keys cannot be operated, check if the keyboard used matches the main control board (whether it contains IC75179). For machines with internal and external keyboard operations, check if the dial switch position you set is correct.
2. If the display is normal, but only some buttons cannot be operated, you can check if the button microswitch is faulty.
