Just recieved my logic probe today. Can you direct me to a guide on what and how to diagnose with it?
There are two ways: The hard but best way and the easier but less conclusive way.
The best way to do it for one-way logic is to get another of the same IC (LS244 for example) and hook it up to the same inputs as the IC you are testing and see if the outputs look the same. The only problem with this is when the IC you are testing is not always enabled and other parts of the circuit control the output lines when the IC you are testing is not enabled. So you will want to check the status of the enable lines to see if this might be the case. For bi-directional components it is more complicated because you will need to build a circuit to check outputs only when the IC is enabled and going in a particular direction.
The easy way is to just power the thing up and write down the logic level of each pin when it is running, then compare it to a known working board. If you don't have a working one to compare it to then just write down what you get and I will try to read the same pins on my MV-4 for comparison. My recommendation is take the top board off completely and start it up - you will get the crosshatch screen. Use your probe to check the state of each pin of the left-most white plastic connector (near the YM2610). These pins are numbered A1-32 and B1-32. Classify each pin as one of these:
N: no signal
L: continuous low
H: continuous high
B: switching between high and low with about equal time in each state
LB: switching between high and low but mostly in the low state
HB: switching between high and low but mostly in the high state