I'm still trying to resurrect a faulty C128D machine that I have. The machine powers on, the monitor detects a video signal and springs to life, but it only displays a black screen. This happens regardless of mode (C64/C128), 40/80 columns or the presence of a cartridge.
I have replaced the entire motherboard assembly in the machine but I still get the same fault, so I am assuming not that the fault lies with the power supply (unless I have two boards with the same fault). I am new to electronics but I want to be able to check that I am getting the correct voltages from the power supply. So my newbie question is, how do I go about doing this?
I have a multimeter but I don't actually know what to test in order to check this. My questions are:
1. When testing, do you need to make sue the power supply is plugged in and connected to the 128D motherboard, or is it tested in isolation (i.e. plugged into the wall but not connected to the machine).
2. Which pins/components do I need to touch with the multimeter in order to perform the test?
Apologies for the dumb questions, but I didn't want to start poking around inside a powered on machine with metal probes without knowing exactly how to go about it.