Below are some quick tips on where to typically look if you encounter specific bugs or issues.

These are not definitive answers, and you can use the other articles on how the system works to more accurately diagnose problems, but still, this is a great first place to look.

If you experience the console locking on and detecting a sync signal (so the TV realises there is a signal) and then either going to solid black screen or no signal (losing sync) it could be the CIA chips.

This is typically bad U12 or traces between it and 68k/Gary/Agnus

This is typically a bad U10 or traces between it and 68k/Gary/Agnus.

However black screen could be almost anything on the en

If using the diagnostics ROM, you will set of screens typically with a bad U10 or traces between it and 68k/Gary/Agnus.

This is typically a bad U11 or traces between it and 68k/Gary/Agnus

Often meaning the lower RAM is bad, it can also be anything on the data path, such as a bad U13 or traces between it and 68k/Gary/Agnus

If using the diagnostics ROM, you will see this set of screens if you have a bad Paula.