UPDATE: Lots of people find this article when trying to fix a stuck mirror on a D70. Chris Inch reports that his D70 mirror would stay up after making an exposure normally. Another shutter button press was needed to return the mirror to the down position. He fixed this problem by using a different battery. If this is the problem you're having, give that a try.
Important: I recommend against taking your camera apart. Though I was able to fix the shutter problem, it wasn't by taking the camera apart. (Read on for my fix, which I also don't recommend you do unless you're prepared to risk ruining your camera. I did it as a last resort.) Taking a camera apart will expose you to a risk of electric shock from the capacitor (the thing that looks like a battery) inside. I'm including pictures in case anyone's wondering what the inside of their camera looks like, not because I think you should do this.
A couple of weeks ago I got an email from my friend Tim who asked me "Do you have any use for a dead Nikon D70s?" He had found it in a recycle bin and told me that if nothing else I'd be getting a spare battery. I have a problem saying no, and a misplaced confidence that I can fix anything, so I told him I'd take it. When I got it, it didn't work - as promised. The battery was charged, but when I pressed the shutter button the mirror would go up but the shutter wouldn't open. "Err" blinked on the top LCD, then after pushing the shutter button again the mirror came back down. No photo. A little googling shows this to be a fairly common occurrence with the D70 and D70s, but there aren't a whole lot of suggestions apart from trying a fresh battery, a reset, and sending it off to Nikon and paying $250 for a repair. I tried the first two with no success, but wasn't interested in the third option. It didn't make sense to spend money on a body that came out of dumpster, especially not when a new D40 body is only $400.
Don't do this. I mean it. If you do it, I'm not responsible for what happens.
I figured I didn't have much to lose by taking it apart. I'm fairly handy and I have a set of small screwdrivers that I rarely use. That makes me qualified in my books. :-) Well it was fun, but I didn't learn much apart from what the inside of a D70s looks like. Interesting, but I didn't see anything to suggest what I might do to solve the problem with the shutter. I put it back together and decided to make it a paperweight while I gave it some more thought.
Really don't do this. I'm still not responsible.
A couple of days later it occurred to me that the shutter might just be stuck. I had been thinking that some little actuator was burnt out or some spring had come off its guide, but maybe it was something simpler. If the shutter was stuck, then what it might need was a nudge. So I nudged it: I lifted up the mirror, took a pair of small, pointy sewing scissors and pushed down slightly with a very small force on one of the little rivets in the shutter. (The topmost one in the photo)
The shutter moved a bit.
Encouraged, I removed the scissors, released the mirror and hit the shutter release. The shutter opened and closed. I went and got a memory card and a lens and hit the shutter release again. A photo appeared on the LCD. I had fixed it!
After a week of happy shooting with the D70s it continues to work perfectly. Realistically, I don't expect a lot out of the camera after what it's been through. Getting chucked in a recycle bin followed by disassembly by a fat-fingered, unqualified dumb dumb on his coffee table, then a highly imprecise shutter-shoving with a pair of scissors is probably not a recipe for a reliable camera. But I hope it is, because in a world that has so few user-serviceable parts I feel great about bringing this discarded camera back to life, and keeping at least one piece of electronic gear out of the landfill for just a bit longer. (Oh, and for free. Did I mention that?)
Some notes: I really don't think you should do this. I did it because I had nothing to lose. When I did it, however, I was careful about dust and what length screws came out of which holes. Note that my shutter was stuck in the "UP" position. I suppose it might just as easily have been stuck the other way. The shutter is also EXTREMELY FLIMSY.
Also, who throws a camera in a recycle bin? Maybe one day that'll work, but until then take it to these guys for environmentally friendly recycling. (If you're in Ottawa. If not, your town probably has an option like this too.)