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On this topic, kapton tape is heat resistant. Wide pieces can be used to protect plastics and components that you don't want to accidentally melt or desolder when you're using hot air. Or tape down something to use as an air (and heat) shield. Hot air alone can be fairly indiscriminate.

My worst lifted-and-torn-pad repair, I ended up buying some two-part conductive epoxy (MG Chemicals 8331, not cheap), cutting pieces of copper tape the size of the pads that needed replacing, and using kapton tape to both help to position the replacement pads and hold them down while the epoxy...

While I'm thinking about it, one other check, this one while the machine is powered up: Check the voltage levels relative to ground on both sides of the inductor.

Okay, the (apparently bomarc?) schematic that someone pointed me to says that pin 11 on the floppy connectors runs to the positive side of C196/C205 (one or the other), clearly decoupling, and also runs through L12 (an inductor, damps noise on the power rail) to the 5v supply. So, check...

Okay, next phase is to check the internal floppy connectors, J16 and J17. Pins 14 and 20 shouldn't be connected to each other (20 is a no-connect generally, and 14 is drive select), but the others should show continuity (though you might have trouble measuring that for the odd-numbered pins...

Looking at my IIfx, the white PSU wire is pin 15, and that's the line that you use to jumpstart the supply if there's something wrong with the startup circuit. Case to pin 1 (yellow): 11v9 Case to pins 2, 3, 4, 5, and 6 (red): 5v13 (+/- 0.01) Case to pins 7, 8, 9, 10, 11, and 12 (black): about...

The Mac-II era startup circuit is weird. There's no standing voltage from the PSU, but if you supply +5v (apparently +3.6v is enough?) to one of the pins it powers up.  If you then ground that pin, it powers down.  The reason why the II has two batteries when one is sufficient to hold the PRAM...

Three or four AAA batteries in a holder plus some wire might also do the trick (you'll be at 4.5v or 6v, I don't know how close you need to get to 5v here). Or if you have another machine that uses 5v (say, a PC?) you could bridge the grounds and then tap the 5v from that for a second. Or wire...

Having my own II-series startup issues (IIfx in my case), I have to ask... have you tried "jumpstarting" the PSU with a separate +5v supply?  That's step one, and should tell you if you need to focus on the PSU or the mainboard.

I'm still reading through the sfcircuits article, but one thing that leaps out at me is the complete lack of version numbers for the software examined, or a date for the article itself.  This immediately limits its utility because there's no way to tell where it may be out-of-date. On my end...

The first couple of times I recapped something, I used radial caps to replace SMD. It works, more or less, but tends to be ugly. In one case, I simply couldn't find compatible SMD caps, so had to use radials, and then had trouble getting the case closed. I very quickly got tired of buying...

Looking at the picture you provided, they both have surface-level traces (easy to expose with a fibreglass pen or craft knife and solder a patch wire to), and both lead to VIAs (typically already exposed, and easy to solder a patch wire to).  Or if you're careful, you could even just leave one...

For powering up without PRAM batteries, google for "jumpstarting a macintosh ii". Long story short, touch 5v between a specific pin on the power supply connector and ground, and it should wake up. For dealing with the battery leakage... I had best not proffer advice at this time. I still...

If the VIAs are surface-mount, it might be as simple as lifting a pin and tying it to the 5v supply. If they're socketed DIP, pull it, bend the pin out, put it back in, and solder a bodge wire to 5v. If they're soldered-in DIP, cut the pin and solder a wire to 5v. Or, in all cases, if the pin...

It'd be nice if 16Mx4 did work, even if such chips still aren't available via Mouser. And https://68kmla.org/forums/index.php?/topic/21519-finally-a-iifx/?p=221669 mentions a prototype involving paired 16Mx4s, a pair of FET bus switches (identified as SN74CBT3244 or similar), and a "five-pin...

But you can pick out an SE/30 by its video card declaration ROM: That won't change when using a 32-bit clean ROM, and might remain even when there's a second video card in the expansion slot. A lot can probably be determined simply by which address ranges trigger bus faults (thus, don't have...

Very nice finds, thank you! And the design on the top part of the cover image of the book (as seen on Amazon) is, IIRC, some sort of modelling software for dynamic processes. I might have to buy a copy of the book myself. The term "Mindstorms" was originally applied to LOGO (and I have a copy...

"Back in the day", probably in the early '90s, the school that I was attending got a Macintosh (IIRC, a Plus), in order to run a program called "Function Machines".  This software appears almost lost to the mists of time, to the point where even Google can find very few references to it.  One of...