Roland TR-909 repair service. In this 909 the volume differences between the individual instruments were too great. The toms, for example, sounded slightly distorted. The battery holder was probably broken during transport and was replaced at the same time.
Sometimes the solution is quite simple. Before me, someone already had their fingers in the 909 and, intentionally or not, installed the wrong potentiometers. The value of some pots was too high by a factor of 10. Instead of a 503 (50k) potentiometer, a 504 (500k) was installed.
I then re-capped the power supply. Here the adhesive that holds the electrolytic capacitors has already had a strong corrosive effect on other components.