Hello friends.
Question, maybe someone has had a similar experience. I received a completely dead Yamaha RX V450, thinking the standby power supply was the problem, but I found that the 10V output was showing 40V!!! I removed the board and worked on it outside the unit, and it turned out Q404 was defective. Naively, I thought, "Okay, now I plug it back in and it works," but it didn't. I got to the board where the microprocessor is located. 10V enters it and drops to 5.5V, C501 was blown. I replaced it, but I'm experiencing some voltage instability on the IC501 regulator output. Just in case, I replaced it with a 78L05 plus a diode on the GND pin to get it down to 5.6V. Now everything is fine, but the unit still doesn't respond when I try to turn it on. I see that there is no +5S voltage, commanded by Q501, Q509 and pin 81 of the micro, I tried disconnecting pin 81 to see if there were any changes and nothing, nor by pin 69 PRY, a signal that enables the relay that feeds the main power supply. The micro oscillator, I could see that it works, but everything would seem to indicate that the 5.6V regulator was damaged and let more than that voltage pass and could have caused the micro to fail, but I understand that the electrolytic capacitors that are at the output of the regulator C502, C503 and C505 which are 6.3V should have exploded as well. Any suggestions or tests to do?.
Thank you very much.
Question, maybe someone has had a similar experience. I received a completely dead Yamaha RX V450, thinking the standby power supply was the problem, but I found that the 10V output was showing 40V!!! I removed the board and worked on it outside the unit, and it turned out Q404 was defective. Naively, I thought, "Okay, now I plug it back in and it works," but it didn't. I got to the board where the microprocessor is located. 10V enters it and drops to 5.5V, C501 was blown. I replaced it, but I'm experiencing some voltage instability on the IC501 regulator output. Just in case, I replaced it with a 78L05 plus a diode on the GND pin to get it down to 5.6V. Now everything is fine, but the unit still doesn't respond when I try to turn it on. I see that there is no +5S voltage, commanded by Q501, Q509 and pin 81 of the micro, I tried disconnecting pin 81 to see if there were any changes and nothing, nor by pin 69 PRY, a signal that enables the relay that feeds the main power supply. The micro oscillator, I could see that it works, but everything would seem to indicate that the 5.6V regulator was damaged and let more than that voltage pass and could have caused the micro to fail, but I understand that the electrolytic capacitors that are at the output of the regulator C502, C503 and C505 which are 6.3V should have exploded as well. Any suggestions or tests to do?.
Thank you very much.
Microcontrollers can partially fail. Force the unit on by desoldering the power on pin from the micro and force it on. See if that works.
I have worked on many items where a single function failed on the processor. Or the entire thing can die. With that event, the voltage was not immediately clamped, the processor was exposed to high voltage for a bit.
I have worked on many items where a single function failed on the processor. Or the entire thing can die. With that event, the voltage was not immediately clamped, the processor was exposed to high voltage for a bit.
