Takes photos without any error but the photos are black

It started with weird shutter noises, when I press the shutter button to take a photo it sounds like I am holding the button to take multiple photos (but sounded much more quiet than usual) after that there was the err message. On the next try it takes the photo normally like always without any problem.

This problem started to occur much more often until the camera stopped taking photos completely. I could hear the mechanism working but the err message was all the time showing and no photos were saved. I wasn't able to change the settings in manual (speed, aperture, iso, wb) the flash wasnt opening.

Since its old camera I decided to change the shutter assembly so I got new one from ebay

I soldered the new one and exactly the same problem continued happening...

So I found this video on yt and decided to do the same thing.

So now err message is gone, I can change modes and settings, flash fires, photos are saved but all of them black with and without lens on manual even on long exposures (I can see the sensor, mirror and shutter are raised) and the camera mechanism sounds normal.

Exposure mode in EXIF is unknown

Any suggestions what could be the problem

Thanks :)