Machine within a louder "squeak" sound common reasons are: a heavy load on the power switch; switch power oscillation frequency is low; core switch transformer, AC power supply filter inductor or line output transformer component loosening. The maintenance of such failure, we must first determine the "squeak" sound parts. Power on, the volume to a minimum, "squeak" sound still exists, that has nothing to do with the audio channel. Careful observation, "squeak" sound from the switching transformer, switch transformer core but no significant loosening. Measurement of switching power supply main power +125V output is low and unstable, fluctuate with the "squeak" sound different. This judge is due to main power heavy load caused by overload and overload phenomenon of instability, it is likely is the presence of line output transformer internal winding partial short-circuit or high-voltage ignition phenomenon. Check the line output transformer high voltage, focusing, acceleration and high pressure parts and related circuit, were not found spark phenomenon, check inverse range capacitance and no leakage phenomenon, then judge the line output transformer partial short-circuit or sparking. Try to replace the line output transformer, troubleshooting.