Open the bottom cover, measure the samsung SF - 700 af CN2 10, 8, 6 switch power supply output, together with the screen flashing out three block voltage and sometimes not. Remove the CN2 connector, when the voltage is sometimes no, specify in switching power supply part (see physical mapping circuit diagram as shown in the appended drawings). Measuring a steady 300 v dc voltage on both ends of the C5, unplug the power plug, voltage not disappear immediately, and at the sound of a switching power supply "zhi", after the 300 v and then disappear. Key check the starting resistance R2, R3 and found the R3 resistance unstable (the most hours 460 k Ω, maximum approximation open circuit), use two 560 k Ω resistor in parallel after the substitution, the machine back to normal.8j4service manual download site