Wednesday, February 25, 2009

CNC repair three-step method

1, power supply circuit
In the maintenance of power supply circuit should first check whether it is normal, and then check the other parts. Power failure has the following forms:

(1) No supply voltage or supply voltage low
CNC system often used ± 5V, ± 12V, ± 15V, ± 24V, using a small number of +3.3 V. The supply voltage is not normal, that is, the system will cause abnormal job. Of emergency equipment, causing equipment and personnel injury, must pay great attention to. Machining center, after boot without any CRT display. Detection system using a multimeter power board A14B - 0067 - B002 - 01, found +5 V power supply voltage of 3.75V, remove the load detection, +5 V power supply for the +4.95 V. Note the low power supply with load capacity or load short-circuit has existence. After checking the normal load. Note decline in power supply with load capacity. After inspection the replacement filter capacitor C36, the system work properly. Tool-free action. Turn off the power supply, power back on, machine tools can work in a period of time. Check all the normal power supply. Fault may be in the system's motherboard. After overhaul motherboard A16B-1000-0220/04A, found two crystal an internal crystal oscillator 16.3840MHz bad, have not replaced the use of the recurrence of similar failures.
(2) power supply voltage detection voltage meter to normal, but Oscillograph detected large ripple voltage waveform. Power supply filter capacitor is normally open circuit, rectifier diode caused by bad or, and sometimes are a component breakdown caused by damage to power overload.
(3) when the system just drive normal, after a period of job decline in the supply voltage. This is usually the voltage regulator circuit or high-power triode bad. In temperature caused by power supply voltage drop, or it may be a component defect, temperature after bad.
No supply voltage or supply voltage severely reduced, the system will cause the disruption or cessation of work, which was easy to detect and find fault. When the power supply capacity with load decrease or filter circuit failure, it is difficult to judge. System it will suddenly stop working, causing
If Units composed by FANUC 3MA
2, the clock circuit
The main clock circuit in the system are the motherboard, it is the large-scale integrated circuits which work in basic conditions. It is crystal oscillator (commonly known as crystal oscillator) for the foundation, in the circuit produce a constant square wave signal. Crystalloid vibration, just like people, like the cardiac arrest, allowing the system to in a paralyzed state. Crystal normal job, the system circuit can be under the command of the CPU clock by crystal beat job. Quantity and frequency of the oscillator with the CNC system vary, but generally at least one, and the remaining requirements of the different circuit clock frequency by dividing frequency of the crystal oscillator circuit or another to solve.
The higher the failure rate of crystal, and its common fault has the following categories:
(1) crystal leakage damage. Multimeter available P × 10K block measurement, if the resistance is infinite, compared with normal; if compared with leakage resistance.
(2) the internal open-circuit crystal. Measuring its resistance with a multimeter though infinite, but in the circuit should not have a pulse oscillation.
(3) crystal metamorphic change its parameters. Only by oscilloscope and frequency meter can detect. Crystal are able to oscillation, but the clock frequency from its nominal value, although the oscillation pulse at this time, but because of the number of error pulses, the system can not work the circuit. At this point only by frequency meter can be accurately measured their deviation.
(4) in the actual clock circuit, the crystal at both ends to have access to have a few to dozens of Paper Paper Act law tiles capacitance, the capacitor leakage, deterioration caused by the clock circuit fault is also more common. Detection of mixed crystal is best to use oscilloscopes and frequency of measurement, it is difficult to assess its quality multimeter.
If FANUC 6M Control Units from the machining center, working for some time, a sudden black screen CRT,
3, reset circuit
Reset circuit is also exist in the system circuit board, which is unique to large-scale digital integrated circuits circuit. Microprocessors, interface circuit and others have reset terminal.
Reset circuit reset pulse generated by the program counter cleared, so that CPU out from the memory initialization file for the control port to initialize the chip. If the reset circuit bad, the system will happen disorders, such as fault crash.
Oscilloscope observation generally reset pulse should be repeated on-off power supply, the switch connected to the instantaneous observation of each reset pulse. Reset pulse should be rectangular ideal square wave. If no reset pulse should be checked in the reset circuit resistors, capacitors, transistors and so on. IC reset the rules of client should be low or high, otherwise, should be reset circuit failure or damage to integrated circuits.
Units like the use of large-scale PLASMA CNC machining center, the system could not be activated, CRT showed no alarm. After inspection ± 5V, ± 12V, ± 24V supply voltage normal, normal clock circuit. Suspected to be the system's motherboard problem, reset circuit in the inspection, it was found that no client CPU reset reset pulse. Further examination revealed a reset terminal 3.3k/0.5W open resistance, the replacement of normal after the system restart.

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