Recently, both of my Hexars developed the dreaded shutter button problem. The buttons went from "fluky" to "completely inoperable" in a few short days, so I decided to attempt a fix and document my steps. It was much easier than I expected!
First, you need to carefully peel back the covering on the front just enough to get at two screws. I found that a tiny flathead screwdriver helped in getting between the body and the covering and leveraging it up.
After removing the other three exposed screws on the top plate, you can lift it up carefully. You shouldn't need to desolder the hotshoe—just position the top plate so it's out of your way.
Using a small screwdriver, open the ribbon cable lock and slide the ribbon cable out. Then unscrew the three screws holding the green PCB to the camera:
Underneath, you'll see the problematic button.
You'll need to pry the metal part of the button off of its plastic base, carefully. I chose to do this in an area where there was no danger of breaking a PCB trace:
It can be a little tricky to catch the metal rather than the plastic when you're trying to pry it off. But when you catch it just right, it'll pop right off:
Removing that metal cover, you'll see a plastic button and metal contact on top of the plastic base:
Carefully remove them, and then clean them. I just used a q-tip and a little rubbing alcohol. Then I polished them briefly with a microfiber cloth. In an attempt to improve contact, I bent the little legs of the metal "crab" piece down, very slightly.
Be sure to clean off the base of the button as well. In the case of one of my Hexars, I think a few tiny specks of dirt on this base were the cause of the malfunction. This button is clearly not very well designed.
Wipe everything with a microfiber cloth to ensure that everything is 100% dry and clean, then carefully reassemble everything, working backward.
Take the opportunity to use a microfiber cloth on the inside of the viewfinder elements. They can get dusty.
When it comes time to replace the top plate, the aperture and mode dials need to meet up with parts on the green PCB. A good method for me was eyeballing it to get it close, partially closing the top cover, and then carefully turning the dials back and forth until they clicked into their places. I also had to push the hotshoe wires around to keep them from getting caught. You'll know everything is correctly in place when the top cover meets up with the body without any resistance.
That's it! Both of my Hexars have been restored to perfect health. Because that button has such a tiny contact, I wouldn't be surprised if I need to repeat this maintenance step every year or two.
I've also posted a gallery of these images
elsewhere. There was once a good Hexar wiki on Silvergrain Labs, but it seems to have disappeared. Until anyone objects, I've posted an archive of that information on Scribd.