YAMAHA RX-V775 - No Stdby LED and no power up for service

[richtoy]

I have a YAMAHA AV receiver RX-V775 with a power fault.
The standby lamp does not come on and it does not power on or enter any service mode.

My fault is identical to the one described in great detail in Japanese on these 4 pages.  Google translate the pages.

https://ameblo.jp/amblog-minors/entry-12467816407.html
https://ameblo.jp/amblog-minors/entry-12467816371.html
https://ameblo.jp/amblog-minors/entry-12467816312.html
https://ameblo.jp/amblog-minors/entry-12467816214.html

Any ideas where to look next?  The Japanese tech got no further...

[ambrosia heart]

I have a YAMAHA AV receiver RX-V775 with a power fault.
The standby lamp does not come on and it does not power on or enter any service mode.

My fault is identical to the one described in great detail in Japanese on these 4 pages.  Google translate the pages.

https://ameblo.jp/amblog-minors/entry-12467816407.html
https://ameblo.jp/amblog-minors/entry-12467816371.html
https://ameblo.jp/amblog-minors/entry-12467816312.html
https://ameblo.jp/amblog-minors/entry-12467816214.html

Any ideas where to look next?  The Japanese tech got no further...

Microprocessor  does not work.    You should troubleshoot standby  board  that is a circuit  board letting AC inputted.  You will see a standby trasformer here.

[richtoy]

The symptoms and all measurements are exactly as described by the Japanese technician in the links.

I have checked the switched mode PSU and all values look correct.  The CPU runs but appears to be halted as noted by the Japanese tech.

[ambrosia heart]

Did you measure reset signal and +3.3M?  They are in phase.
Did you measure microprocessor  waveform?  If all voltages on standby board are OK and reset signal as well as microprocessor  crystal waveform is correct,  microprocessor  is dead.

[richtoy]

I have been busy with other stuff but have now got this Yamaha back on the bench.
The crystal waveform is correct, 8MHz

The +3.3M and reset are both 3.3V from when the power is applied.  Is this what you mean by in phase?

What I have noticed is that after power is applied the standby light does eventually come on (after 90 seconds) and stays on for precisely 24 seconds and then goes out for another 90 seconds.

This on/off with an off of 90s and on of 24s appears to carry on indefinitely.  The period is really quite precise.  During the 24 seconds that the standby light is on the amp still does not respond to any inputs.

Anyone seen such behavior before?

After examining the boards carefully IC4 and IC943 have been replaced after production but IC943 appears to function correctly for the 24 seconds that the standby light is illuminated.