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After taking many photos without problem, the mirror on the D90 suddenly started jamming - movement gets part way, but image comes out black or extremely dark, sometimes with a partial image at the top, suggesting the jamming position varies. After some groaning of a motor against whatever is jammed, the mirror eventually releases back to view-finder position. The first time it happened, after a couple more cycles, it successfully took a photo, then jammed on the next. It intermittently works after a long rest, then jams again after one or two shots. The LCD shows "err" when the jam happens.

If the lens is removed upon jamming, the mirror is in the up (or mostly up) position. The shutter is closed.

When no lens is attached, everything works perfectly. The problem happens no matter which lens is attached.

Based on this Q&A, we tried a new battery, and that did not help. Note that this answer addresses D40 and similar, but the "main drive wheel" described is completely different on the D90, so that did not help. Lubrication of the visible gears, part of the Aperture Motor Gear Assembly, didn't help. Also, because all works when lenses are off, it suggests that's not the problem area.

Based on the same answer, we tried lubricating the "pivot around which the shutter and mirror cocking mechanisms rotate", as per the instructions given. That seemed a more likely target given its engagement with the lens, but that didn't help either.

A factory reset had no effect.

Short of completely dismantling the camera or taking it to an expert repairer, is there anything else we can try to free up the mechanism or prevent further jamming? Is there anything that might explain why it works perfectly with no lens, and only jams with a lens on?

oCn
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  • Just a WAG, so not an answer, but my hunch would be that there's a fault in the main board that could be causing a voltage drop when a lens is attached and the associated circuitry in the main board is active? When a lens is not attached and that part of the board is not active there would be no fault. Whatever it is, you've pretty much eliminated everything that would not cost more than the camera is worth to get it repaired. – Michael C Feb 15 '23 at 17:06
  • Do you have any "non-CPU" lenses available to test with? These would be either older Nikon F-mount lenses or newer "non-chipped" third party lenses that are not detected by the camera. If you tried to shoot in any of the automated or semi-automated modes with a non-CPU lens the camera would give a "lens not detected" message forcing you to use manual exposure (with no metering capability). – Michael C Feb 15 '23 at 17:17
  • @MichaelC, thanks. It seems odd in that case that it works on briefly intermittently, but I guess that enough charge could build up to overcome the fault at times. We don't have any lenses older than around D90 vintage, but it's a good idea nonetheless. I'll try a couple of newer lenses, just to explore. On the lenses we usually use, we've been shooting in manual exposure mode, but I guess the camera does still meter in that case... – oCn Feb 17 '23 at 14:19
  • Is it possible your camera's mirror has sort of slid down the frame holding it to the point the mirror is striking the back of the lens? Of course that would mean a good part of the frame would not be visible in the viewfinder. Or is any other part protruding from the lower part of the mirror frame? – Michael C Feb 18 '23 at 05:59
  • @MichaelC, nothing seems out of place and occasionally the camera takes a photo as normal. When the mirror unjams, all looks normal through the viewfinder. My guess is a lubrication failure somewhere we can't get to without disassembly, but was hoping there was something I'd missed. I'll report back after trying a more modern lens. – oCn Feb 19 '23 at 07:39
  • My advice would be to use a less modern lens with no electrical contacts. Of course you'd have to shoot in manual mode with no metering. Just be sure if it's a really old pre-AI lens (pre-1977) it has been converted (Nikon used to do it for about $20 back when they first made the change to the F-mount that added a metering ring on the camera's lens flange) so it won't damage your camera if your D90 has the metering index ring on the lens mount. – Michael C Feb 20 '23 at 01:09
  • OK. That looks like more a long-term project, in that case, but thanks for your comments. It especially seems like a good prospect for if we can't manage to repair the mechanism. – oCn Feb 21 '23 at 08:28

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