There are several undocumented features here. If you enter the tests page and hit control-A, some extra tests are enabled. Hitting control-K enters a keyboard test. Hitting control-F enables a low level hard drive format option.
You can select which devices to test and then enter a diagnostic loop. Hit control-pause to terminate the loop.
Errors are logged to the parallel printer port (if enabled) and also stored to memory. Hit control-E to look at the in-memory copy.
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