Hi, I have a 3 year old Onkyo TX-SR506 receiver that I bought secondhand. The receiver can get very dusty so I was cleaning the top with a damp cloth while listening to music. Suddenly the music stopped and it hasn't worked since. I tried resetting the receiver, tried other channels, radio channel/headphone channel both do not work. Also if I try and configure the level calibration I don't get a sound either. I did notice that when powering up I do not hear the normal 3 clicks that I used to hear, I just hear 1 click (like a switch being turned on/off). I did try and open the case to see if there was anything unusual that I could see, but I'm no expert and I didn't notice anything unusual. Can anyone help me with this? It would be much appreciated!

It is possible that while you cleaned the top with a damp cloth , some drops of water could have fallen on the board and shorted. If so it is possible that the amplifier had encountered a fault with a higher current drain which had triggered it to a protection fault condition. The fault can be your output drivers- the MOSFETS/IC's fitted for both the channels, Use a meter after disconnecting to check for short in the drivers. Disconnect the positive and negative voltages to the output and see if the protect changes. Even a fault in the preamp stages that drives in high current into the output can shut the Amplifier. Sometimes this can be a noise like a HUM or HISS before the protect works. Faulty capacitors in these circuits also can cause similar issues and needs close observation.
You need to confirm and replace the specific stages or outputs. If not there can be issues in the mother board, maybe the protect circuit by itself is shutting off due to a faulty bias , maybe a leak in any voltage/current sensing circuit. Also disconnect the speakers and test, if the protect is off then check for short on the speakers.