Onkyo TX-SR507 Stuck in Standby


The typical Onkyo (well most amplifiers) fault. The amplifier switches into standby or protect mode after a couple of seconds.

Amplifiers switching into standby or protect is usually caused by something triggering the protection circuits. More often than not something in the main amplifier output stage has failed such as a power transistor going short which puts DC from the power supply rails onto the speaker output.

If you have either a positive or negative DC voltage on the outer ends of the big white three pin resistors (often 2 x 0.47 ohms) by the power transistors the protection circuit will be triggered. You should measure it with the volume control turned right down and no source selected.

Typically you get get a voltage on the resistor if one of the power transistors has failed. Be aware that the preceding transistor(s) and components might have also failed.

In this instance three transistors had failed on the centre channel, one of which is one of the main output transistors. Presumably one failed and took the other two with it.

There are a lot of boards in these amps, but it’s possible to get all the main boards out without taking everything apart which saves you breaking connectors and refitting cables.

The back panel needs to be fitted as it links the 0v connection to different boards so repairing these receivers can be time consuming.


Before fitting the new parts I checked all the other transistors on the centre channel that drive the main output ones.

On power up it promptly destroyed both the centre channel output transistors where only one had failed before!

These are complex amplifiers and high voltages and currents are at play so I’m not entirely surprised it failed again. There’s also a lot of fake power transistors on the Internet and I might have fitted a fake.

This would be a good excuse to fit a modern TDA7293 based 100w amplifier board as shown below in place of the failed channel.

Home theater amplifiers have at least 5 individual power amplifiers in them and a failure in any of them will shut the amplifier down. A lot of the transistors in older units are obsolete making them difficult to source although most transistors have modern day equivalents.

These TDA7293 boards cost about £5. The three failed transistors in the Onkyo  cost more than double that.

TDA7293 circuit board

Obviously fitting it into an existing design isn’t that simple as the power supplies in big amplifiers are often in excess of what the TDA7293 can handle plus you have to attach it to the existing heatsink with an insulating pad as the metal tab is connected to -VCC the heatsink in the amplifier is connected to 0v.

A bit of work, but cheaper than buying a new receiver.

If you know nothing about electronics don’t attempt a repair. These have high voltage and high current power supplies in them that could do a lot of damage or give you a nasty shock.