A st 5300A AV Amplifier, boot both Dolby Pro Logic, Dolby three channel mode selection, or choose to bypass, a test state, anterior and mid channel all silent around the track in the state at the end of the first sound. Keying or remote control of its screen display are normal.zUDservice manual download site
The machine is a popular AV amplifier by Dolby authentication, the whole function and operation of the whole machine is shown by a CPU (UPD78042) management. The selected audio signal through the buffer after entering decoding NJW1103, l, R, C, s four channel signal output, both the Dolby / straight choice, equilibrium, volume control, pre amplification (LM833), respectively, into a monolithic integrated amplifier tda7294 of amplification; and mid, ring around channel signal directly through the LM833 amplification volume control enters the last set successfully put a piece of amplification (C tda7265 tda7294, s). In addition when starting from CPU MUTE end sends the squelch signal, the implementation of the TDA7294 and TDA7265 through the squelch squelch circuit.zUDservice manual download site
Now l, R, C, silent, and s channel Dolby Pro Logic and test is sound and screen operation normal, can basically eliminate CPU control display and Dolby decoding before part of the circuit fault, focus on examination of Dolby decoding and after switching, before release, volume control, final amplifier, static noise, L/R/C integrated power amplifier power supply circuit. Open shell after three tda7294 8, {15} feet, and 7, {13} feet, negative supply voltage examination were normal. {14} feet in the output end of the connected components are not damaged, well connected; disconnect R38 (R45, R33) audition headphones are pre sent audio signal machine back to normal.zUDservice manual download site
Maintenance analysis: amplifier in playing music in the protection relay is always opened a, seems to be the midpoint voltage output, but measured midpoint voltage for normal zero volts, measuring amplifier tube B pole voltage is about 0.5 is normal. Before measuring the positive and negative supply voltage, + B only 18 Volt B has - 56 volt, voltage is obviously unbalanced, because the relay power supply is from B, the direct use of a 620 European /2W resistor current limiting power supply, voltage relay only 8 volts (normal should is 12 V), voltage relay enough so you can't pull.

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