Pioneer VSX-421-K not turn on

I understand that you’re facing an issue with your Pioneer VSX-421-K receiver not turning on, even after replacing the transistors Q422 and Q417. You’ve also checked the main fuse and transformer, and they seem to be working fine.

Given the symptoms you’ve described, it’s possible that the issue might be related to the protection circuit in your receiver. The protection circuit is designed to shut down the receiver if it detects a problem that could potentially damage the unit or cause a safety hazard. This could explain why your receiver turns off after 2 seconds.

Here are some detailed steps you can take to troubleshoot this issue:

1. ***Check for DC Offset***: The protection circuit can be triggered if there’s a DC offset at the speaker outputs¹. You can check for DC offset by measuring the voltage at the speaker outputs with a multimeter. The voltage should ideally be close to 0V when no audio is playing. If you detect a significant DC offset, it could indicate a problem with the output stage of your amplifier.
2. Check the Protection Circuit: The protection circuit itself could be faulty. It usually consists of a relay and some associated circuitry. If the relay is not clicking on when you power up the receiver, it could mean that the protection circuit is not functioning correctly².
3. Check Other Components: Other components in your receiver could also be faulty and causing the protection circuit to engage. This includes other transistors, diodes, resistors, and capacitors in your amplifier’s output stage¹. You can check these components with a multimeter or an oscilloscope.
4. ***Check Error Log and Reset***: There’s an error log that can be run and a reset procedure that might help². From the OFF/STANDBY state, press & hold [PRESET <–] & [ STANDBY/ON] buttons. Release when the unit powers on. Each press of [ENTER] key displays a protection error count. To reset errors, from OFF/STANDBY state, press & hold the [ALC/STANDARD SURR] & [STANDBY/ON] buttons. Release when the unit powers on. The unit will display “CLEAR?” Press [ENTER to reset error and error logs|new_window=true]².

Please note that these are advanced troubleshooting steps and require some knowledge of electronics and experience with electronic repair. Always make sure to disconnect your receiver from power before attempting any repairs to avoid electric shock.

Feel free to ask questions.

@alperbeysim here is the service manual for this series. Remember that it shares the amp board where your transistors failed,with a few other models in the series. I would start by checking that particular board. That schematic is identical in that series. The power supply etc may have some differences but you can check those against your boards. the voltages etc. will most likely show faulty or as not existent because there are still faults on the board. I would not expect those to be accurate.

I could not add the file on here due to its size (33MB) https://drive.google.com/file/d/18cD6XtJ...