Yamaha RX-V677 no response

[MaLe20]

Hi, I got Yamaha RX-V677 which doesn't want to start. No standby LED either. I inspected power board and no problems there. 5.6v to digital board, AC power detection etc measures correctly. I check signal going to main IC and all looks fine there. Inspected vcc pins on main IC and 3.3volts goes there. Same for EPROM. Same for the button 3.3V pull down and trace back down to logic shifter. Disconnected some cables that are not necessarily to start didn't helps either. I am a bit puzzled as I am not sure what other criteria must be met to allow unit to boot. Has anybody seen this kind off issue or might have some other ideas where to look. Any input more than welcome.

[MaLe20]

Re: Yamaha RX-V677 no response

I think I am getting close. I started to look into other power sections and I found that on Both IC944 and IC943 there is no Voltage coming out. 5.6 V goes in but nothing goes out. Schematics in the attachment. Any advise more than welcome

[R_J]

Re: Yamaha RX-V677 no response

Those ic's both have ENable pins , the ic's are likely not turned on. As for the micro, check the reset circuit.

[MaLe20]

Re: Yamaha RX-V677 no response

You are correct lack of enabler to run DC-DC converters. As you said I looked at Reset circuit and I draw attention to DFF_FROM_N_RST line which is connected to D type flip flop IC81. This sends enable signal to DC-DC converters giving other voltages on digital board.

DFF_FROM_N_RST line comes directly from Microcontroller IC83 pin 92. Signal stays high at this line and D entry on flip flop which comes from same microcontroller is low. If I am correct to get flip flip to pass correct output I need D to be high as well.

Is there a chance that EEPROM is corrupted?