1, the power supply circuit in the repair <br> <br> should first check the power supply circuit is normal, and then check the other parts. There are several cases of power failure:
(1) No power supply voltage or low power supply voltage.
CNC systems often use ±5V, ±12V, ±15V, ±24V, and a few use + 3. 3V. If the power supply voltage is abnormal, it will cause the system to work abnormally.
(2) Use a voltmeter to detect that the power supply voltage is normal, but the oscilloscope detects that the voltage waveform ripple is large. Usually the power supply filter capacitor is open circuit, the rectifier diode is bad or the virtual solder is caused, sometimes the breakdown of a component causes the power load to be too heavy.
(3) The system is normal when it is turned on, and the power supply voltage drops after a period of operation. This is usually a bad regulator circuit or a high power transistor. When the temperature rises, the power supply voltage drops, and it is also possible that a certain component is soldered, and the contact is poor after the temperature rises.
When there is no power supply voltage or the power supply voltage is seriously degraded, it will cause the system to interrupt or stop working. This kind of fault is easy to detect and discover. When the power supply has a reduced load capacity or the filter circuit fails, it is difficult to judge. It will cause the system to suddenly stop working, causing sudden accidents of equipment, causing equipment and personnel injuries, and must be highly valued.
For example, a machining center consisting of FANUC 3MA does not display any CRT after power on. Using a multimeter to detect the system power board A14B - 0067 - B002 - 01, found that the + 5V power supply voltage is 3. 75V, remove the load detection, +5V power supply is + 4. 95V. Note that the power supply has low load capacity or a short circuit in the load. The load was checked to be normal. The power supply has a reduced load capacity. After checking and replacing the C36 filter capacitor, the system works normally.
2, a clock circuit <br> <br> clock circuit mainly on the system board, which is the basic condition on which LSI work. It is based on a crystal oscillator (commonly known as a crystal oscillator) that produces a constant square wave signal in the circuit. The crystal stops, just like the human heart stops beating, leaving the system in a paralyzed state. After the crystal oscillator works normally, the system circuit can work according to the beat of the crystal clock under the command of the CPU. The number and frequency of crystal oscillators vary with the CNC system, but there is usually at least one. The different clock frequencies required by the remaining circuits are solved by the frequency divider circuit or another crystal oscillator.
The damage rate of the crystal oscillator is high, and the following faults are common:
(1) The crystal leakage is damaged. It can be measured with a multimeter P × 10 K block. If its resistance is infinite, it is normal; if there is resistance, it is leakage.
(2) Open the inside of the crystal. Although the resistance is infinitely measured by a multimeter, an oscillation pulse cannot be generated in the circuit.
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