My nephew’s Rockjam keyboard came back with me after we did a sponsored walk together. The keyboard takes a 10V DC wall-wart power supply, and was exhibiting signs of hiss and hum. I initially checked that it wasn’t a failure of the power supply’s rectification by attempting to run it using another supply – the problem was still present.
Opening it up, I can see from the main board that there are two electrolytic capacitors that had pinhole ruptures on their tops.
These were 470µF/16V and 1000µF/25V. The latter appeared to be a smoothing capacitor, operating in a pair. All three were replaced with electrolytic capacitors of the same value, but higher voltage rating to improve longevity.
Upon powering up afterwards, the idle on the keyboard was practically silent.
Of Sound Mind 