Recently got this Technics SA-TX50 receiver in decent condition and trying to troubleshoot...
Power up, the relay clicks and "Tuner" source was selected using 'Stereo" mode".
Increasing the volume from 0 to -55 dB, a faint humming is comming and both VU-meters stuck at 0.1 and the sound is weak and distorted.
Changhe the input source to front VCR3 connect an analog signal from a DVD player...same result!
Removed the cabinet and visual inspect for damaged parts...find out main-board has some heat (dark) discoloration on D709-712, D725-728 and Q701-702 area!
As per service manual pag. 37 that is power supply and regulator for +B5 and another regulator for +B8, +B9.
As per page 58, the output voltage of Q701 shold be 5.2V ...measured is 5.15V and ICP701 is ok, also tall cap C711 looks fine (again visual).
The voltage at CN1101B is 10.5V and supply power for IC1114 and IC1115 (respectively +B8 and +B9), both IC output 5.04V.
During the measurement, I check the temperature on diode bridge and Q701-702 and are getting really hot.
My understanding is +B5, +B8 and +B9 are 5V voltage low current for video/audio input selector and A/D convertor, DSP IC.
Before start digging and remove the main-board, did I miss something here ?
Last thing, removed the link between the decoder and power amp and the decoder output signal is same weak and distorted!