Restoring A Vintage IBM I/O Tester

By now, [CuriousMarc] and his team of volunteers are well versed in 1960s hardware restoration. So when a vintage IBM I/O Tester came into their possession, a full machine makeover was all but inevitable.

The I/O Tester dates from around 1965, which roughly coincides with the introduction of IBM’s lauded System/360 computer mainframe. In addition to the computer itself, business customers could order a variety of peripherals with their computing system. These included storage devices, printers, additional operator consoles, and so on. Since these peripherals shared the same I/O design, a portable hardware testing rig was a sensible design choice. One portable low-voltage tester could be paired with any number of IBM peripherals, doing away with the need to have unique debugging panels on every piece of computing hardware.

Fast forward to the present day, and the IBM I/O Tester looks positively antique with its blinkenlight lamp panel and switches. To use the tester, simply connect up one (or both) of its chunky 104-pin connectors to your IBM peripheral of choice, insert the accompanying paper overlay, and voilà. Operators could then observe the status of the many lamps to evaluate the inner digital workings of the connected peripheral. Depending on the connected hardware, the tester could reveal the contents of data registers, printing status, disk and tape transfer status, and probably much more. The purpose of the tester’s ninety indicator lights is completely dependent on the attached peripheral, and the paired paper overlays are essential to comprehend their meaning.

After [Ken Shirriff] deciphered the documentation, it wasn’t long before the tester could be powered up using 24 VAC (normally supplied by the equipment being tested). Several burned out lamps were noted for replacement. The lamp assemblies required minor surgery due to a dubious design choice, and at least one of the toggle switches needed a new guide and a heavy dose of contact cleaner before it came back to life.

For the moment, [CuriousMarc] is using the blinkenlights panel as a surprisingly striking retro clock. With a literal truckload of vintage IBM hardware sitting in his storage, it’ll be exciting to see whether this restored tester will be pulled back into operational service someday. Readers should also check out our coverage of his previous major project, restoring an Apollo Guidance Computer.