Tandy MS-DOS Diagnostic Package TS1288 Readme

The diagnostics package will allow the user to test a Tandy MS-DOS computer and its expansion boards including various I/O ports such as parallel, serial, floppy, and ST-506 hard drive interfaces.  The diagnostic will also test the floppy and ST-506 hard drives for proper operation.

Includes:

Test points for voltage measurements.
ROM-based diagnostic software allows testing of a computer that cannot boot from a drive.
Diskette-based diagnostic software lets you test other I/O and drive operations.
LED display on the diagnostic board will display the current test in progress as well as provide a diagnostic code should the unit fail to boot fully.

Notes:

A later hardware diagnostic board was designed that include IDE hardware testing.  This board built, beta tested, and functioned fully.  It was never funded for production.