* ist D, DS, DS2, DL and the just plain K100D
This sequence, embedded in one of the quotes above, has been tested and confirmed on the original * ist D and the K100D (non-Super) both with 1.00 firmware. It is claimed on DPReview to work for the models in between but I am unable to confirm that.
*istDS, debug is built-in, no need for a modset file.
procedure: During switch on, press the AEL-L and INFO buttons at the same time.
After that, you have approximately 5 seconds to press the MENU button twice, then the INFO button. Voilá!
Edit: You now see the debug menu, the cursor positioned on the first item DEBUG <OFF>. Change it to <ON>.
To cancel debug mode, start the camera the same way, but now confirm the "DEBUG <OFF>".
---------- Post added 10-14-17 at 12:29 PM ----------
This is the story of how I came to gather this information and post it all together here in one place as Mike suggested so long ago.
I started shooting film in 1955. Around the turn of the century I explored digital with a Canon A300 and later an S70. After carefully researching DSLRs for a long time I bought a new * ist D, which I liked very much. In fact, I wore it out. Over the years I bought on eBay a used K100D and K100D Super and liked those, too. And another * ist D to replace my original -- for sentimental reasons. (It has pro features missing on the 100 series, but the 100s have some updated features, such as SD cards and a bigger display.) During a flush period, I decided to go full-frame, and after waiting a long time for Pentax to do the same, I bought a Canon 6D. I didn't like it at all so I sold that and bought a Pentax K5. That was OK but I found I liked my little Pentaxes better, so I sold the K5 as well. I don't really remember what possessed me to buy a K10 -- possibly finding one with a very low shutter count from a reputable seller on eBay -- for about $60 as I recall. I loved it! It looked brand new and took great pictures -- except for the fact that it kept locking up on me and refusing to take pictures. It had a 30-day return policy and I debated the whole 30 days and consulted with the seller, who offered a full refund, but had no idea how to solve the problem. After much experimentation I concluded that the problem was that when trying to focus on a distant object, the motor in the body would push the lens up against the stop at infinity, still not feel things were in focus, and so block the shutter release. (Later I discovered that the camera
would work reliably with a rarely used Pentax/Tamron 18-250 zoom, presumably because the focus ring will go past infinity.)
Here and at other sites online I found out about debug mode. I decided to keep the K10D and sit on it until I got up the courage to mess with debug mode. In the meantime I bought another used K10, That cost more and was not in as good apparent shape, but it always worked. It became my default camera. I monitored things online and more info appeared and I was able to sort out some apparently conflicting information. Then my K100D Super developed the same problem! I tried replacing that with a K200, but that never felt right in my hands, though I have kept it. So, I decided to take the plunge into debug mode and see if I could get my K100D Super back as well as a second working K10.
I gathered up all the info I could online, then went through it and tried to distill what seemed most likely to work. I saw Mike's post here, as well as innumerable posts from others seeking this information, or saying the posted instructions did not work. So I decided to test the instructions for any camera I owned and post the results here. The outcome for me is that both cameras now work fine. The K10 needed a +150 adjustment to work with all my lenses, while the K100D Super only needed +100. (I live in New Hampshire so it is not hard to find distant mountains to focus on.) I did NOT make any attempt to get anything to focus perfectly. I was only interested in the more basic question of whether the camera refused to take pictures. Because I do not own any Pentax cameras newer than a K200, I don't expect to add cameras to this thread, though I welcome additions from others. I also welcome questions or corrections to what is posted here. I would really like this to be a one-stop source for people having focus problems. The fact I did with two out of seven Pentax DSLRs suggests the problem is not rare.