The thing about measuring zero volts is that the place you're measuring could be an input; could be an output at zero state; could be disconnected entirely from everything.
So once you see it's zero volts, turn everything off and measure its resistance to ground. Reverse the polarity of the ohmmeter leads and measure it again.
Zero ohms means it's grounded. Infinite ohms means it's open. A resistance measurement that changes when you reverse the polarity means it's connected to some semiconductor circuit, whether output or input.
Zero ohms that rapidly increases to some high value means the major item connected to that thing is a capacitor.
How much do you understand about input and output circuitry?
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
