Zenit-3m Mirror issue

Hey guys,

I recently picked up a Zenit-3m from someone on Facebook marketplace, probably not the best place to buy cameras as you will soon find out.

I've shot a roll of film on it so far, and everything worked fine up until I was doing some test winds yesterday night.
When I wind the lever, the mirror goes down to create an image, but before the shutter is fully wound the mirror automatically returns up, and there is no viewfinder image. The camera doesn't have an instant return mirror.

After poking around in the front of the camera, I found out that the mirror is not coming down far enough to get caught on the catch. When I help it out a little, it catches and everything works fine until the next wind.

Is this a problem with maybe a spring being worn out, or something else nasty?
I would appreciate any help in fixing this camera as I really don't have the money for a technician at the moment.

I assume the solution is somewhere here:

Thanks for digging this up for me.
This should help, I’ll have to have a close look at it.
Do you happen to have the whole manual available?

The page is from the manual on the successor model E, which already got the return-mirror. But I guess it is of some help nonetheless and you can sort things out in the graphics. I got both models, but admit I did not explore the mirror control yet.

https://learncamerarepair.com/product.php?product=866