Below is a video in which I discuss a pitch bend problem in a Korg Synth MS-10. The main thing is how to look at the schematic and determine what voltages should be present in the circuit.
Where the fun begins is when you don't have the voltage present and you have to figure out why.
The + and - 15 volts D.C. are the output of a typical analog power supply in equipment from this era. This goes to the pitch bend pot that can affect the voltage.
As you turn the pot it gives the desired output voltage that the synth player is looking for to drive other modules on the synth. The customer's problem is that is wasn't working at all. The problem ended up being an oxidation buildup on the molex connector that connects the pot pitch bend assembly to the main board where the power supply components reside.
So it was a simple repair but in the video you can see how I came to this determination and also by studying the schematic.