You press the power button on the stereo, it comes on and then after about half a second it automatically turns off and the standby light flashes.
Flashing standby light on the Onkyo CR-505 DAB means that the 'Overcurrent Protection' circuit has activated. This circuit is connected to the power amplifier board and will activate if there is a problem on the amp board. It will also activate if there is a fault with the speakers or speaker wiring, so for an initial test, unplug both speakers and plug in some headphones to see if the fault is still there.
If the fault still occurs, then its probable that either the Left or Right channel of the amplifier has blown and this fix should help. Test each of the 2SB1559 transistors (Q253, Q254) on the main amp board. A bad transistor, in this case, will have a short circuit from collector to emmiter.
If Q253 ( left channel ) is bad, replace: Q253 - 2SB1559, Q527 - 2SC1845, R543 - 0.22, R551 - 10K.
If Q254 (right channel) is bad, replace: Q254 - 2SB1559, Q528 - 2SC1845, R544 - 0.22, R552 - 10K.
Note: R543 and R544 are 1 watt resistors! Do not use standard 1/4 watt ones or they will blow.
How to do the Repair:
Important Note: It goes without saying, but always unplug the stereo before working on it!
Start by taking the lid off the stereo, and then remove the 2 screws that hold the plastic frame that covers the heatsink and pull the plastic bit off. Next, remove every screw you can see on the back of the stereo.
When all screws are removed, slide the mains cable out of its place. You should now be able to carefully lift the metal back plate away.
Gently lift the tuner section (the bit with the aerial sockets) and fold it back on its flat-flex cable and let it rest on the top of the CD player.
Look down where the tuner was and you will see a vertical long brown connector. Unplug this connection and feed the wires out to the back of the stereo. it may be a tight connection and you will probably have to gently wiggle it to get it apart
Next, unplug the white connector from the amp board, and follow the other white wire up to the board with the speaker sockets on it and unplug that.
The amp board should now be free and you can work on it easily. Remove all the screws that are holding the all of the transistors to the heatsink, and remove the single screw from the circuit board side. The transistors have probably adhered to the isolating heat transfer pad, so whilst holding the heatsink, gently tap each corner with a screwdriver handle and this shock should seperate them.
Now you have the seperated board you can replace the damaged parts. Observe which way the flat side of the 1845 transistor is facing and be sure to place the new one the same way or you could do more damage to the stereo. The 1559 transistor must always be fitted with the metal bits nearest to the heatsink and the writing facing outwards. Resistors are not polarised so can be fitted either way. You should replace all of the parts I list, even if one or two test ok, as they will all be weak now.
Thats it! Now put it all back together and you should have a working stereo again. Good