These handheld diagnostic tools were sold to Apple service people for about $1000 (USD). They load their tests from ROM 'packs', two of which were included with the unit. They can test almost everything on a Macintosh from the ADB ports to the FPU using a built-in 4 x 16 character black and white LCD. The TechStep is connected to the host Macintosh via several cables that connect to each port of the computer allowing complete access to all interfaces present on the computer.
6 different ROM packs made by Apple and own 3 of them (see chart below). Most of which are designed to test the RAM, floppy drives, power and SCSI voltage, hard drives, CPUs, video memory, monitor and other components of specific Macintosh models whereas the Apple SCSI HD Tests pack can only test drives connected to some Macintosh models or directly to the TechStep. Almost all tests can be run in a loop to discover intermittent problems.
They able to test and diagnose hardware malfunctions using a hidden 'Test Manager' program built into the Mac's boot ROM that could be evoked by a diagnostic tool (the TechStep). The testing procedure works with the TechStep being connected via the SCSI and either the modem or ADB ports at startup. When the power on self-test (POST) is running and the 'happy Mac' is on screen, the TechStep sends the command to enter testing mode where the Mac is halted and a 'sad Mac' appears and the system is now under control of the TechStep. Once the system is halted, the TechStep tests the first 33 KB of system memory and loads its software into that section before testing can begin using the appropriate ROM pack.
The TechStep can be powered by either the included 9-volt power adapter or a single 9-volt battery and includes a carrying case, which holds the unit and accessories.
With its simple menu interface the Apple TechStep is very easy to use. By following the onscreen instructions you can perform any test included in the ROM pack you're using very simply.
Results gathered from testing with the TechStep are stored on the unit and can be transferred to a Macintosh computer via the serial port on the side of the unit using an included program and a standard Mac serial cable. A Macintosh computer is also capable of testing the TechStep itself as a damaged testing unit can cause more problems than it's worth. More info at www.forcedperfect.net
Apple Tech Step Software
Apple Tech Step - CPU Test ROM Module