Pentax KX viewfinder black after winding

My Pentax KX (almost same as K1000) goes black upon winding the film. When I fire it goes back to normal until I wind again.
Took the lens off and it doesn't look like it's stuck on anything. looks like a mechanical lock that keeps the mirror up.
the mirror flips down once I fire.

any ideas how to fix that?

thanks in advance.

http://www.cameramanuals.org/pentax_pdf/pentax_kx.pdf
Manual page 24 - self timer
Manual page 25 - mirror lockup.
ensure these levers are at their home positions. exercise them and return to home position.

Thanks but tried that already. It’s stuck in up position every time I wind. When I fire it flips down regardless of the position of the mirror lock lever.

Sounds like its repair time. Do it, the KX is a fine camera.

I'm thinking it has something to do with the mirror box. I dunno if the KX has cushion in its assembly the way a lot of SLRs do, but after a while, these cushions deteriorate and can lead to various problems.

The KX is a classic workhorse and is, to me, one of those cameras that is worth spending the money on for repairs. If kept up, I don't see why cameras like the KX and others in its "workhorse" class can't last well beyond the century mark. Its tech is already almost 60 years old. (It has a lot in common with the Spotmatics of the 1960s). So yeah, I'd just find a competent tech and have it gone through. I wouldn't be surprised at all if it ends up being a simple repair.

Just dropped it off at Kanto Camera and they said the same thing. Something is wrong with the mirror box.

I know this is gonna get me in trouble again with the righteous people but I am gonna say it anyhow. This camera just got back from a second round of CLA at the famous Pentax repair shop in the U.S. Not going to mention the name this time as it got me in trouble here last time when I 'bashed' the well known and inexpensive Leica repairman (not the same as the Pentax guy) in the U.S. for messing up my summicron three times in a row and charging me for it.

I bought the camera online (in Japan), sent it off for CLA and light seal replacement just in case. It came back and didn't look that different. The finder was still dirty and after half a roll the shutter was locked completely. Sent it back and was told a piece of plastic was stuck in the mirror box, whatever that means. I only put a roll of film in there no plastic pieces... This time I only paid for shipping. Got it back and it worked fine for 2x 24 exposure rolls. On the third roll the mirror issue happened.
I bit the bullet and paid Kanto to do a full overhaul. Roughly 250 USD, but they will take it apart completely. Check each single part and clean, lube and replace if necessary.
Kanto knows the history of this camera now and will take pictures of each step. I'll report back here with what was wrong and what was overlooked during the last two CLAs.

I know I could've bought another body and hoped for the best, but I am sick of going to used camera stores. I just wanna shoot the camera.