You need to check voltages on your PSU before doing anything else. In the past, I posted detailed PSU voltages that you should have a look at.
Check the voltages at the floppy connector on the back of the SE/30, as shown in this photo. My photo is showing the point to test the 5v line. If you are seeing something less than 4.85v, you may want to tweak the voltage adjustment POT inside the SE/30's PSU (which means you have to open the PSU to do it). Even if your 12v line rises to 12.5v or falls to 11.9v, it's nothing to worry about. And in my experience, the 5v line is good to go from 4.75v to about 5.15v.
Check the voltages at the floppy connector on the back of the SE/30, as shown in this photo. My photo is showing the point to test the 5v line. If you are seeing something less than 4.85v, you may want to tweak the voltage adjustment POT inside the SE/30's PSU (which means you have to open the PSU to do it). Even if your 12v line rises to 12.5v or falls to 11.9v, it's nothing to worry about. And in my experience, the 5v line is good to go from 4.75v to about 5.15v.