This Does Not Compute | Restoring One of Apple's Weirdest Vintage Macs! @ThisDoesNotCompute | Uploaded March 2023 | Updated October 2024, 2 days ago.
The Macintosh IIsi was a midrange model from late 1990 meant to go up against PC clones in business environments. But some of the compromises that its engineers had to make to hit its price point meant for some very interesting quirks.

Branchus Creations: https://www.recapamac.com.au and youtube.com/branchuscreations
BlueSCSI: bluescsi.com
MeowTOAST: github.com/Stephen-Arsenault/meowTOAST

Hakko FR-301 desoldering iron (affiliate link): amzn.to/3mNuER6

Sources:
MacUser, December 1990.
"Can new Macs restore shine to Apple's future?," Computerworld, December 24, 1990.
IIsi NuBus adapter card photo: recycledgoods.com/apple-820-0303-02-nubus-adapter-card-for-iisi
IIsi NuBus adapter card scan: applefritter.com/node/2076
DayStar dual-socket PDS and cache card riser photo: applefritter.com/node/10199
"Mac IIsi," Macworld, December 1990.

00:00 - Introduction
01:52 - Disassembly
03:08 - Recapping the PSU
05:33 - Completely pointless soldering montage
06:04 - PSU surface-mount caps
06:30 - Tanta-lizing motherboard repair
08:23 - Quirks and features, part 1
08:59 - It blew up! (Not really.)
09:37 - Further testing
10:31 - BlueSCSI version 2
11:52 - Tidying up
12:51 - Uh oh
14:51 - Quirks and features, part 2
17:17 - One-slot wonder

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Music by Soundstripe (https://www.soundstripe.com) and Epidemic Sound (https://www.epidemicsound.com).
Intro music by BoxCat Games (freemusicarchive.org/music/BoxCat_Games).