After the machine is powered on, DC IC5400 (STK390-910) convergent block temperature, switch on after a long time. The IC is burn out. Along with burned out IC5813 (12V-terminal regulator blocks).


STK390 -15V II foot measuring normal ⑥ foot +12V normal. STK390 ① foot measuring 4. 5V DC voltage is normal. II measuring 4 feet. 5V DC voltage is
Often. But with an oscilloscope waveform, saw II foot 0. 2Vpp line frequency square wave, the third toe the line frequency square-wave output of 12Vpp. ③ foot under normal conditions should be ± 5vpp field of line frequency square-wave frequency modulation, II the pin should be 4. 5V pure DC voltage. Should not contain line frequency square-wave components. Search from STK390 II foot forward, found Q5403, Q5402 b, e very much wave deformation, c5404 measuring 11Vpp across the line frequency square waves that normally should be O. 8Vpp line-frequency triangle wave. Change
c5404(0. Μ f 001), troubleshooting.