RE: Inspiron 17 5748 does not recognize external microphone
Many thanks for taking the time to provide such a detailed response.
I wonder which document said that you can use "just a microphone" with an Inspiron 5748 combo port? It might be difficult to find a stand-alone mic with a TRRS plug.
I went back and reread the documentation to which I referred. I had made a mistake, I was reading a general statement about ALL audio input jack options and thought I was reading one related specifically to the headset. I am not really interested in using the older, two-plug headset as it is low quality with deteriorating ear pads. (I was trying it only as a test.) I know I can buy replacement pads, but I would normally consider it easier to just buy a new headset (though this hasn't proven easy at all!)
That is the right type of headset you need to get the mic function of the combo jack to work, although I don't know anything about that specific headset. It could be that the jack is defective. Or it could be a buggy Realtek driver. It could be that the impedance of the mic is different enough from what the jack sensor is set for by the driver, that it fails to sense the mic.
Yes, it could be that the jack itself is defective in the laptop, which is out of warranty. Oddly, the laptop had the same problems with the Logitech h540 headset, which is a USB headset. I've reinstalled the driver several times, and believe I have the newest one. A mic impedance mismatch could certainly be a cause; I hadn't considered that.
Here is another thing you could try on the software side of things. Go back to Sound>Recording tab. Right click on "Microphone". Click on Properties. Click the Advanced tab and uncheck the "Exclusive Mode" box if it is checked. Test the headset mic. There is a small chance that this will help, but probably not.
I gave this a try, but as you anticipated, it didn't work.
I think I will try to find a TRRS to USB adapter and see if that works, since I already have the h151 headset.
Again, I greatly appreciate your help and detailed reply.