First off, if you don’t already have a copy, get The Dead Mac Scrolls. If you can’t buy a printed copy, you can access a scan of it from here: The Dead Mac Scrolls 1992 : Free Download, Borrow, and Streaming : Internet Archive
Fixing your Mac shouldn’t be hard, but you may require software tools (compatible disk repair/format utilities) and a long-handled Torx screwdriver (if you need to replace the hard drive).
I highly doubt you have a motherboard problem. A flashing question mark usually indicates a problem with the hard drive. Either it’s missing, non-functional, or it doesn’t have a bootable System folder.
Can you boot it from a floppy? If you do, can you see the hard drive?
If so, it might just be a matter of re-blessing the system folder. Drag the System file out of it and then back in (making the special “system” icon appear on its folder icon). Then try to reboot.
If it boots from a floppy, but can’t mount the hard drive, can you see it with some disk repair utility? I don’t know what software you may have, but if any disk utility can access the drive, then it is physically working. See if a repair tool (like Apple’s Disk First Aid or Norton Disk Doctor) can repair it. If that doesn’t work, then can you reformat it? Of course, reformatting will lose all your data.
If the drive isn’t accessible to repair software, then it may have failed. Hard drives from this era are known to suffer from sticktion, where the heads stick to the platters, preventing it from spinning up when it is next turned on. A quick workaround for this is to remove the drive, shake it (horizontally, in the same plane as the platters) a bit to see if that can dislodge the heads. Then connect it and try to boot up.
If that worked, don’t turn the computer off again. Immediately make a back up of the drive’s contents. Then replace the drive. If the stiction dirve-shake didn’t work, then the drive may be completely dead. You’ll have to replace it but won’t be able to make a new backup.
For a new drive, you should be able to use any 3.5" SCSI drive. Use the smallest drive you can get. Everything you can buy will be larger than the SE/30’s original drive (up to 80MB). Don’t get a drive larger than 2TB - the computer probably won’t support it and the APT partition table format doesn’t support anything larger than 2TB.
If you have a third-party drive formatting tool (like LaCie’s SilverLining or CharisMac’s Anubis), use it to partition and format the drive and install the necessary “driver” file. If you don’t have either of them, you can use Apple’s HD SC Setup utility, but it needs to be hacked in order to work with non-Apple drives. See also Apple HD SC Setup - Wikipedia
WRT how to physically replace the drive, iFixit doesn’t have a repair guide, so you may need to do some web searching if you want step-by-step directions.
I haven’t worked on an SE/30, but if it is like my SE, here’s a quick summary of what you’ll need to do:
- If you installed the debug keys in the ventillation slots, remove them.
- Remove the four case screws. You will need a Torx T15 screwdriver with a long shaft (at least 12") in order to reach the two screws inside the handle well.
- Place the Mac screen-down on a soft cloth (to prevent scratching the screen) and remove the back cover. You may need to pry it off. Be careful to avoid damaging the plastic if you want to keep it looking good.
- It’s a bit cramped in the case. Be sure to not touch the CRT or the analog board (which has some high voltage capacitors) to its right.
- Disconnect the drive’s SCSI and power cables.
- Use a long-handled (preferably magnetic) screwdriver to remove the screws that connect the drive’s mounting bracket to the top of the floppy drive. With these removed, you should be able to remove the bracket, with the attached drive.
- Remove the screws attaching the drive to the bracket. Remove the drive.
- Attach your new drive to the bracket with the same screws. Then screw the bracket onto the floppy drive and reconnect the cables.
- At this point, power-on the computer to make sure you didn’t break anything. Boot a floppy and make sure your utilities (whatever kind you’re using) can see the new drive. Then shutdown and power off again.
- Close up the case and reinstall the screws.
- Boot a floppy, partition/format the new drive. Restore software from your backup.