One channel brighter/ louder than the other Yamaha RX-V530

[kasumyku]

Hi everyone,

I'm trying to figure out what can cause one of the channels to have brighter sound than the other.

So far I have opened it and saw some very light oxidized connections so I sprayed them and the volume/bass/ treble knobs also speaker output connections/RCA inputs with electronic cleaner (I also used a small plastic brush to remove the oxidation)
I've checked the bias and both channels show same reading.

Any suggestions would be much appreciated.

p.s.: Already changed speakers + wires with new ones to eliminate amplifier,but same result.Tried same speakers with a different amplifier and they sound OK.

Thank you in advance!