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Case # 658700  06.19.2025    Pioneer SX-850 sound distortion in right channel on Phono input only.


Nice receiver . Build to last. Troubleshooting   –  Problem in Phono preamp board only. All other inputs working perfect. You have 6 transistors on phono preamp board . 3 – for left channel , 3 for right channel. While unit working  we touch plastic body all those transistors by hot soldering  iron tip  for 2-3 seconds. On one of them  sound distortion increase after touching – that is  indication that transistor is bad, even if it tested ok by tester . In this case was 2sa725 transistor with red dot on top. We use KSA992 instead original. Transistors pinout is different but parameters are  better for this specific use. It is always better to use same part if part available. We  support rule -minimum change to original schematic – that is repairman major goal. For good balance in two channels we changed same transistor in left channel. We guess these transistors are going bad  after   wrong input signal  connected to Phono input  1/ Phono input 2  ( from CD , cassette players, phone or Bluetooth .)c