This is a quick grab on the way out of work with the Tamron and Pentax 1.4x HD TC. 280mm f5.6 1/160 ISO 200 hand held on my K-3
Run it through Lightroom quickly, uncropped. If you want the original RAW let me know.

I had what I thought was a SDM failure on my 16-50 but it seems if you don't use it often it "goes to sleep".
I found that by twisting the focus ring back and forth and pointing it up while pressing the AF button then down and press the AF button many times it appears to have woke it up. Try it before you send off for expensive repairs.

No message just a piezo action and a very quiet chirp sound

I use the Pentax 1.4 HD TC and it is excellent. Tack sharp and AF is not compromised.

You have a PM

Exposure compensation checked, green button pressed and factory default reset performed to no avail
I suppose the number of shots over time will differ with each user and so the problem will materialise at different times for all users. However it would have been nice if Pentax had taken responsibility and recalled.

A friend in work bought a K30 (stormtrooper) on my recommendation for her daughter, she loves it
However Rebecca, the daughter, rang me the other day and was worried that all her recent photos were dark.
Did some rudimentary troubleshooting over the phone and everything seemed in order so it was dropped into work today for me to have a look.
Diagnosis ...
All lenses, including SDM, will stop down to the minimum aperture, regardless of what is displayed on the rear screen, on every shot but if I put on an old lens with an aperture ring the lens then stops down to whatever the aperture ring is set at.

Can anyone help?

I had one a while back, great way to get good length on a budget. In good light it was fine. They have a weird doughnut bokeh but I didn't mind that.
These were taken using the brilliant Pentax exclusive Catch in Focus.
https://flickr.com/photos/45965924@N03/sets/72157627370159164

Although I could probably process them better these days

This was taken 2 days ago in my garden, I remember as a kid (70's) not having any ready for St. Davids day on March 1st.
Fuel for the Climate Change Crowd.

I like the second cheesy heart shot