RX-V750 this model is rare in the amplifier repair, symptom of this amp is turned on power up no responses, instruction light not on, screen is not lit, there is no relay suction sound. This phenomenon within the industry to three trouble-free, but unlike other appliances without is often due to a power short-circuit, burning fuse, and amplifier of three noes are generally caused by the CPU is not working, because almost all AV amplifier is small 5 volt power transformer direct supply, CPU controlled relay connected main transformer power supply. Small transformer circuit only a few Watts of power, usually without breakdown.bYgservice manual download site
bYgservice manual download site
After open the cover test normal CPU power supply and standby 5 volt power supply, using oscilloscope waveform normal CPU Crystal about Crystal oscillation. This machine is one of the higher end Yamaha AV amplifier, CPU M30622MHP-189FP, standby signal to the CPU after the Start button is pressed,bYgservice manual download site
bYgservice manual download site
And then by the CPU to start main relay, CPU working condition including the power, reset, crystal oscillator and clock signals. Based on past experience, bad cable connection is also common and Yamaha amplifier fault, therefore, I would check all connections, by measuring the cable plug of the M19 has found rusting again boot properly after processing.bYgservice manual download site
bYgservice manual download site
Typical cable M19R the foot of the measured voltage is as follows:bYgservice manual download site
SW:0 SWE:0 MTFS:-12 PRY:4.7 SBRY:4.7 ERY:4.7 MBRY:4.7bYgservice manual download site
ZZRY:0 40NM:4.7 8/4:4.7 PRV:1.6 PDET:4.6 /RES:4.9bYgservice manual download site
+5S:4.7 +5M:4.7 S10:9.9 MG:0 VP:0 These voltages may be helpful to maintenance,bYgservice manual download site