[Mr Carlson’s Lab] saves a Fluke Model 407 high-voltage power supply from the scrap heap, and demonstrates carefully troubleshooting the vintage device to track the cause of the bad output down to a single capacitor. In the process, we get a close look at what is inside as well as insights on how to meaningfully service a device like this.Firing up old electronics should always be done with care. Some electronic components don’t age well, and some faults aren’t always visible. Applying full power to an vintage device could cause considerable (and avoidable) damage. [Mr Carlson] powers up the device using an isolated transformer and a current-limited variac, but another classic approach would be to use a dim-bulb tester, which most folks could cobble together from spare parts.Glorious vacuum tubes where one would otherwise expect transistors.While destined for the junk heap, this Fluke Model 407 actually looks to be in pretty good condition. There’s no obvious damage or failure in its vacuum-tube-and-circuit-board internals, and it powers up but the main output doesn’t act right.[Mr Carlson] walks through the entire process of tracking down the fault, demonstrating everything from safe power-up and basic inspections to signal and component checking. This process is aided by having access to the original schematics, and the problem is ultimately narrowed down to a faulty capacitor in a feedback signal responsible for keeping the output voltage constant.It’s not a full restoration, but rather a clear demonstration of diagnosing a hardware error thanks to a careful and informed approach that keeps the specific challenges of vintage electronics in mind. Watch the whole thing in the video, embedded below.