First in head around channel feet entered interference signal, and (first will amplifier machine volume potentiometer adjustable to smaller location, and so as not to damaged sound van), and around channel sound van has obviously of "Ka wipe" sound, and told Ming around channel signal channel normal, and suspected is head fault, and measuring head impedance around two channel resistance each for 260 Europe, and head normal, and Hou suspected is tape and head in put sound State Xia contact not in place, and by check no problem, and last suspected is power circuit has problem? Measuring output pin voltage of 26V power supply 7812 (more than 1 time times higher than normal 12V), 7912 logging output to 16V (normal is negative 12V), 5V D1406 output foot log, normally. Good obviously 7812 and 79,123 end integrated regulator lC internal regulator circuit appeared fault, and replaced 7812 and 7912, and power are 12V and negative 12V recovery normal, and but fault still, and due to no circuit diagram, and only from power circuit backward level circuit tight trace, and Dang hand touch R303 and R306 Shi, and R306 temperature is high (hot), and R303 and R306 respectively is are 12V and negative 12V circuit of points pressure resistance, and (Told Ming R306 zhihou of negative 12V circuit has components overload or short-circuit), and this two road voltage has been with Cong to IC 8A07 (total 42 feet), and 1th feet for are power feet, and 22nd feet for negative power feet, and measuring 1 feet has are 12V, and measuring 22 feet voltage for zero, and by check is received in 22 feet of 12V regulator diode short-circuit, and caused 1 c 8A07 no negative 12V work voltage, and replaced 12V regulator tube, and fault excluded, and put sound and recording full normal8Xdservice manual download site