Analysis of maintenance: all the output voltage wires disconnect the power board (Model 715T2828-3-FQ) on, at no load, power supply output voltage measured deputy only 4V, seems to malfunction in the standby power supply circuit. The aircraft standby power chip TNY277,2Ymservice manual download site
TNY277 is an efficient offline switcher IC, associated with the series also TNY274, TNY275, TNY276, the difference lies in the different output power. In AC85V ~ 265V, the output power TNY277 about 8W, output power IC other three were 5W, 6W, 7W. The series IC built a 700V breakdown voltage of the MOSFET, oscillator, high-voltage current source, it is now widely used in LCD TV, DVD, set-top boxes switching power supply.2Ymservice manual download site
    Measured regulator light lotus light emitting diode voltage across approximately 0.3V, indicating that regulators detection circuit detects that the output voltage is too low, the optical coupling has ended, but described the primary power supply problem. 300V measured voltage is normal, Shoumo TNY277 surface temperature. When the secondary load, the chip temperature rise, indicating that the primary load is heavy, causing chip overcurrent protection. Based on experience, the switching transformer and spike absorbing circuit can cause a problem with over-current protection. The investigation Z911 are measured positive and negative resistance 300Ω. Z911 model P6KE 160A, which is an overvoltage protection tube, normally large impedance when the voltage across the reaches 160V breakdown conduction, overvoltage disappears and then returns to high impedance. Now the measured resistance is very small, apparently damaged, because I hand no such element, then refer to other circuits After a 47kΩ / 1 W resistor instead of troubleshooting.2Ymservice manual download site