Finding a broken trace on my old Mac with the help of its ROM diagnostics (opens in new tab)

Yesterday, for the first time in about a year, I tried powering on the Macintosh Performa 450 (LC III) from my past writeup about Apple’s backwards capacitor. It didn’t work. The screen was black, it played the startup sound, and then immediately followed up with the “Chimes of Death”. Nothing else happened from that point on. Here’s what it sounded like: