K-r exposure problem

My K-r is producing very underexposed (black) images. Out of the 50 or so test shots I've taken, about seven have a very faint image. When I switch on the bright/dark setting, in both review and playback, this shows that the basic features of all the images are recorded to a limited extent. All the images were taken in program mode and some of the exif files/properties show aperture/time/ISO settings which could have been suitable for the subject. I have tried a variety of possibly camera settings, SD card re-format, reset and a manual lens to exclude lens coupling. I am now wondering if it is a software problem. I did let the battery drain to exhaustion and maybe that corrupted the software.
Any similar experience or ideas will be most welcome.
Thanks Bob

hopefully it's not the aperture block failure of the K30/K50.

Thanks for that lead David, as I wasn't aware of the aperture block issue. I have looked up the thread about the K30/K50 and it mirrors my experience very well. My K-r precedes the K-30 by a couple of years so it's disgraceful that Pentax allowed it to affect so many models. I have tried some of the suggestions and some of them work. Setting an aperture of f32 worked and so did using an old manual lens. I think my results confirm that it is the dreaded aperture block and I shall have to consult a repairer. It's obvious from the posts that contacting Pentax is useless, which is very disappointing and undermines my confidence in the current Pentax brand.
I may add to the other thread as well as this one if I make some progress.

Kind regards, Bob

Yes a good test is to use a manual lens, set to a fixed aperture, and see if that produces consistent results (as in confirm the camera is metering correctly).

Thank you Richard, from reading the other thread I know you are an expert on this subject.
I don't normally use manual mode so I'm having to read the manual to get consistent results. I'm working on it.

Bob

Wouldn't go that far, but yeah, it happened to my K-30

Haven't heard of it on a K-r though, so I guess I was wanting to diagnose it a bit more, in case it's a metering mode, or a lens specific issue.

Good luck!

I was pretty sure it is the aperture block problem, so I took it to a repairer in Bristol. I explained the fix that was well detailed on a YouTube video that had proved successful but he didn't buy that and wanted to send it to Pentax. I now have to bite the bullet and do the job myself. First I have to find out more about the filing operation. Is it to reduce the length of the magnet or just to clean the ends to improve contact. The video shows the ends finely polished so my guess is the latter purpose. I will let you know how I get on.

Bob

Good news and very bad news. I was able to do the magnet filing on Sunday afternoon in about two hours. Was much easier than I had expected. On first test I thought it was working fine until I realised I had not engaged the AF/M button with the switch inside. I had to dismantle the camera again and make sure the button was in the right place. When I then started testing again I found real problems with the exposure. I won't describe all the ways I tried to determine what was causing the problem but just summarise the general effects.

Using a 50mm lens with an aperture ring set to the A position, the camera starts on it's capture cycle and then stalls for 5-10 secs before the shutter opens. With the lens off I watched this sequence. When the shutter release is pressed the diaphragm trigger rises a little way and the mirror is raised then after the pause the shutter opens and closes normally but no image is taken at all. The same thing happens using a DA lens.

Using the 50mm lens in any manual aperture position produces a well exposed image. The review screen always shows f1.7 the max aperture but by watching the lens aperture in action it was stopping down. Without checking the manual, I think this is normal for non-DA lens. So the problem revolves around the automatic exposure system.

I have wiped the camera and lens contacts but they are passing the AF signals anyway. I reset the settings and checked the custom settings and the only thing I am thinking of doing is reinstalling the firmware. I don't think my work on the aperture block could have caused this issue but who knows (no black exposures).

I am hoping that someone may recognise this problem and suggest a remedy.
Thanks for reading this catalogue of woe.

Bob