Because of this machine after the thyristor protection, cannot be to protect the detection circuit of voltage measurement, therefore, adopts the method of one by one to remove protection for maintenance. Specific in two steps: zk4service manual download site
 zk4service manual download site
1. Eliminate overvoltage protection switch power supply zk4service manual download site
 zk4service manual download site
Line with wires to the output pipe Q781 base and the emitter circuit, or disconnect Q781 base, make the line of the output circuit to stop working, and out of line output overcurrent protection and overvoltage protection; On both ends of a + B and output C909 300 q / 50 w resistor in parallel or 60 w bulb do dummy load, boot + B voltage measurement. If a + B and output voltage is normal, Q902 no longer protection, fault line output overcurrent or overvoltage protection circuit; If still protect, too high or a + B + B output voltage switch power supply voltage over-voltage protection circuit element metamorphism, the error protection. At this time can disconnect ZD909 or will Q902 extremely G with short circuit, the control of remove protection measure + B voltage, voltage is normal, if a + B fault in a + B voltage over-voltage protection circuit, common for the zener diode ZD909 leakage or voltage value decreases, and the partial pressure resistance R922, R923 resistance change; If a + B voltage is too high, failure in CP901 sampling error amplifier circuit. zk4service manual download site
 zk4service manual download site
2. Out of line output overvoltage and overcurrent protection zk4service manual download site
 zk4service manual download site
After determined + B voltage switch power supply, remove the dummy load, restoring line output circuit. Caused by open circuit in order to avoid the line flyback capacitor over voltage protection, first check or replace line flyback capacitor C781 (9100 pf / 1.6 kV), then boot test, if after startup, everything is normal, and no longer protection, fault is caused by open circuit line flyback capacitor. If protection, still can be used individually disconnected protection circuit Q902 G very zener diode ZD753, ZD752 boot experiment, observation method of maintenance fault phenomenon; If disconnect after which diode, exit the protection state, and the sound, light, figure is normal, is the protection circuit element metamorphism, caused by error protection, common for the zener diode leakage or voltage value; If exit protection, grating dim, line output tube heating, + B fault phenomenon such as voltage drop, is caused line output over current protection; If grating light, line output voltage rise "secondary", is the line output overvoltage protection.

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