Rod Hull's Vintage Computer PSU Tester Looks Like "A Microwave That's Had an Idea"

The Future Was 8-bit (TFW8b)'s Rod Hull has had a bright idea — cartoon-style: a low-voltage direct-current (DC) power tester that has been described as "a microwave that's had an idea," thanks to a top-mounted car brake lamp acting as a load.

"This is in fact just a thing I knocked up for those 3.42 times in your life, when you wonder if a DC PSU is up to snuff," Hull explains of the compact gadget. "Well, I don't know about you, but if a 40 year old [power supply unit] says 1.4-amp 9V, I'd often wonder if it could really meet the spec. Now the convoluted way of checking would be to dig out a multimeter and check, a lazier way is to plug something in, that could display approximately what's what… and rather than risking yet another brown-out on an old 8-bit, test it on a safe and practical load."

Hull's primary interest lies in classic computing hardware of multiple-decade vintage. Most of these systems rely on an external power supply that takes alternating current (AC) from the wall and converts it to direct current (DC) at a particular voltage. As the power supply ages, that voltage can change: if it drops too low, it won't reliably power the system; if it goes to high, it could damage something. In either case, there's always the possibility that the power supply is still outputting the correct voltage but is unable to cope with a sustained load — something that's harder to check with a multimeter.

That's where the "microwave that's had an idea" comes in. The 3D-printed case holds a simple off-the-shelf combination voltmeter and ammeter, which provides a live read-out what the power supply is putting out — while a car brake light bulb serves as a resistive load: if the bulb doesn't light or is dim, the PSU's struggling. The tester can also sit in-line between the power supply under test and the device it's designed to power, providing a live view of the actual power draw of the system plus the bulb.

A project write-up is available on TFW8b.com, along with STL files to 3D-print your own tester.