At a wedding recently, I lent my camera to someone as I wasn't able to take photos due to other commitments during the service. When it was returned, the flash wouldn't lock in when I put it down. I put it down to something being broken and was going to take it to a service center to have it looked at.
Another AusPhotography member posted about the exact same issue at about the same time I had mine. I thought I should google it, and boy was I surprised when I did - lots and lots of D90 users (and other Nikon DSLR models) were experiencing the same issue. There's plenty of 'solutions' around such as sticky tape, blue tack etc - none of which are really practical if you need to use the onboard flash.
After some hunting around though, I found some information about an adjustment that you can easily make to the catch. The information I found was for the D50 but the flash unit on the D90 appears to be nearly identical, at least in terms of its retaining pin.
I was able to fix mine within about 2 minutes, preventing the need to take the camera to a service center (2 hours drive away for me!)
What is required:
- 1.5mm hex driver (Allen Key) (roughly 1/16" for Imperial)
- Fairly clean desk
- A couple of minutes
- Torch (optional)
- Turn on the camera
- Release the flash by whatever means necessary so that it's in the up position
- Turn the head of the screw circled in the picture below.
- Test the flash and see if it stays down!
I suggest only small movements (1/6 of a turn) of the screw in one direction (either clockwise or anti-clockwise), testing the flash lock (ie. pushing the flash down) between each increment. I would not suggest turning more than a full rotation of the screw so keep track of where you are up to. If, after a full rotation in one direction you have no success, turn the screw back to the start point and proceed in the opposite direction.
If you use a torch and shine it in the rectangular hole above the screw while turning the screw, you should see the catch moving.
All being well the above will get your flash locking again. If it does not, then I'm afraid that I will not be able to help you further as there may be a missing part inside. This is just the process that worked for me.
If the above does not work, read below for a method that worked for a few people who read this article.
If you're game enough, you can remove the back cover of the flash unit. You will need a small philips head screwdriver to do this. Be warned - the wires in the back of the flash are live! At this point you should turn off your camera, remove the battery and I would suggest let it sit for a good 15 minutes for the capacitors to lose some charge before proceeding to take off the cover. Also try to avoid touching the wires if you can! Note that I don't personally condone this method or take responsibility if you injure yourself or your camera. Opening it up is done so at your own risk.
Once inside you can remove the catch that you have been rotating from the outside and cut a little bit off it. It's plastic so using a sharp knife will achieve this easily. The catch is thinner on one side but it seems in some cases it might not be thin enough. Once you've cut a bit out, put it all back together and try again - hopefully you have more luck!
While there's not really any way to hurt your camera doing this, you do it at your own risk. I am not liable for any damage you might make to your camera or yourself. If in doubt, take it to an authorised Nikon service center!
Adjustment screw, circled in red