Understanding Pro95 earphone jack operation

[rrman987]

How I analyzed Pro95 earphone jack operation:
Inserting a mono plug, the tip opens contact 2 and 6 muting speaker, and 2 provides audio to earpiece. Contact 3 touching the plug sleeve provides ground to earpiece. Contact 3 blade forces contacts 4 and 5 open, opening earphone jack barrel.

Inserting a stereo plug the tip opens contact 2 and 6 muting speaker, and 2 provides audio to left earpiece. Contact 3 touching the plug ring (middle) provides ground (and thus audio) to right earpiece. With contacts 4 and 5 opening contact 1 earphone jack barrel, removing the stereo earpieces common ground, places the two earpieces in series, creating mono x 2.

My question is what function does contacts 4 and 5 serve opening the jack’s barrel contact 1 with either type plug insertion? Or am I not understanding how the jack operates?

 

[CycleSycho]

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Hint? It is in the same physical location of 2 & 6, meaning it serves to (after speaker is broken) continue the signal through to the item plugged in (depending on two or three 'rings' on the plug).


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