If OP think something is broken in his second hand synth, give us an example of one button that does not lit up?
What causes confusion is asking for the number of buttons?
- if anybody say 8, how does that help?
Some are true toggle feature, on/off, some are selection of what is active like LFO's, some initiate menu to set a value with parameter and other inititate menu and let you use both parameter and value knobs to set that.
With all respect, kind of a lot to explain.
if you suspect one should lit up and doesn't, name those and we can explain, maybe?
Assign source and destination does not lit up due to that they are not on/off thingy. Just inititate menu or hold to directly move a knob etc.