I bought this defective X0XB0X on the web with the intent of fixing the unit.
So the issue it that the output volume is very very low.
Where do I go from here, what could be the problem(s) and or how do I find out what's causing this?
I have zero knowledge of electronics, that probably won't help, but I would still like to give it a try
First, it would be worth a try to reheat the all the soldering joints in the synth section i.e. top half of the x0xb0x pcb and check J5 connection to the IO board pcb; to eliminate possible bad contact/dry joint issue.
If that doesn't help, then you can use a multimeter in AC mode to check for signal strength. You can program/play a pattern with a single note to keep the signal constant, have all the pot setting on the x0xb0x turned to minimum except the TUNE knob.
Check VCF for output
Measure with a meter in AC 20V mode or look on the CRO at R96 connecting C14
Check VCA for output
Measure with a meter in AC 20V mode or look on the CRO at C38 connecting to Volume pot.
You should get at least >1V at all of these points.