IBM 4685-K03 - Manual (Page 39)

Chapter 5 Maintenance of the keyboard 23
Mode switch test (Self-diagnostic test)
Switching the mode key switch to a new position should cause the speaker to beep once.
MSR Test (Self-diagnostic test)
If a magnetic card is scanned through the MSR, the speaker should beep twice.
Key Input Test (Self-diagnostic test)
Pressing any key should cause the speaker to beep twice.
Note: This test does not work if the position of the mode key is pointing at “Inactive”. The mode key switch must be
in one of the other positions.
How to terminate the self-diagnostic tests
To terminate the self-diagnostic tests, turn off the POS terminal by pressing the standby switch.