MM 5387aa - WesClox

IC:MM5387AA-N
how: Short pin 38 to VSS(Ground)

 

In this Westclox example, pin 38 is the 24Hour SELECT pin.  The next pin, 37 shows that it is connected to Vss (ground) when using a multimeter.  The pin-out diagram shows this as having no connection. I have tested this with a jumper wire from pin 38 to the solder pad on pin 37.   This resulted in the display switching from reading 5:27pm to 17:28, as shown in the following examples.

Note that you could flow some solder from Pin 37 to 38.  This would "permanently" switch the clock to 24 hour mode.  I have no issue with this, but for the sake of convenience to "normals",  perhaps you could jumper this to a new switch mounted in the back of the clock cabinet. This would allow the next user(s) to select between either 12 hour or 24 hour mode.

Provision for more switches

Based on the datasheet of this IC, it looks like this alarm clock could be further modified with two additional switches. Perhaps even a double throw switch as these two features would not be used simultaneously .  This model clock does not make use of a SECONDS display.  I could install a momentary switch to Vss (ground) that would display the seconds of the current time.  This might be useful when attempting to synchronize this clock with another.  This is on pin 32

Also, another switch to Vss (or the other throw of the same switch), would show and enable SLEEP time if this clock were utilized in a clock-radio device.  This is on pin 30. However, if you are going to take take advantage of this, consider what you would use it for.  It is intended to trigger a relay when enabled. This relay powers on a radio circuit and subsequently turns off this same relay after a specific amount of minutes (SLEEP). The SLEEP trigger is pin 30, the output is on pin 27.  Also, consider Figure 6.  This indicates to me that the SLEEP enable switch not only connects pin 30 to VSS, it must also break the connection for OUTPUT COMMON SOURCE. This would be pin 23

Display Intensity

To Be Added

Datasheet:
http://pdf1.alldatasheet.com/datasheet-pdf/view/9252/NSC/MM5387AA.html