OK... a recap to what I messed up this week - and the week isn't over yet: the CD-Drive wasn't reading stuff properly so I threw in a cleaning disk. It now doesn't read at all. The PowerMac 4400 floppy drive is possibly dead and keeps the thing from booting. Turns out a PCI-to-USB card I was trying to use sends my PowerMac G4 into an absolute conniption (it shows a garbled "you must restart" message) and Windows (98 through 10) don't notice it at all - so that doesn't work at all. ADB keyboard and mice are so horribly overpriced it's not even funny. Makes me want to ditch the PowerMac 4400 and get a 486.
@Joe This is a HUGE help. Thank you.
The black mark on the top of LF1 isn't related to it being burnt. It's some kind of marking that appears on this component.
The highlighted resistor is just black in colour. In fact, no component is burnt/scorched. No funny smells either.
I'll give the rest of your trouble shooting a go and report back.
@JDW Thank you for your reply too.
I've checked the voltage output of the converter and it's right on the money. It's also at 60Hz and has a rating of 100w. No no issue there.
Will, do you have a multimeter to test the voltage coming out of your step-down converter? And is the frequency of 60Hz correct too? Even if the voltage and frequency are correct, what happens when you connect another 120VAC device (other than your Mac) into that converter? I am trying to make sure you are getting good power going into your board. If you are, then of course diagnosing your analog board will make sense. And the things others have suggested are quite good. You basically have to troubleshoot the board on a component level to find which component is causing a short, since that would be the only thing on the board itself that would repeatedly blow the fuse.
And now for something I really didn't need and spent too much money on.
SE/30 in 'extra mature' yellow. 4MB RAM, 20MB HDD (working!), currently running 6.0.8 but that'll change. It's a little 'used' cosmetically but nothing above some light scrapes and general yellowing. The seller claims it's been recapped too, so I can't complain too much.
I've rather overspent on the vintage Macs this month so I won't be doing anything particularly drastic to it for now. Next month, however, I'll up the RAM to 32MB and get looking for an A/UX-compatible network card.
@cheesestraws does some 68k programming so may be able to help, possibly.
There was also the guy who wrote some 68k software so that he could add Wifi functionality to System 7?
In terms of this matching the Micron Xceed functionality, will it also provide support for an external colour display?
@maceffects Sign me up for the non-Linux version, I am primarily interested in getting the Micon Xceed functionality at a reasonable price.