Could somebody help? I have a problem: almost suddenly the F on my Yamaha 674 is not sounding any more. A quick inspection shows that one of the two the associated keys is not closing properly. The failing key is the one that closes together with the key I close directly by pressing my index RH finger. It is the fourth key on the body section counting from the foot tenon.
I cannot send it to the technician at this moment.
I looked for adjustment screws but I do not see any related to these keys. It had a COA not so long ago (about a year)

Any help?

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Update: Looking more carefully and with a good magnifying glass I found an adjusting screw for levelling the failing key and my F is back fine. I had to screw-in about half a turn which looks rather much. I wonder what had happened. If anybody knows has any idea please post.

<Added>

Update: Looking more carefully and with a good magnifying glass I found an adjusting screw for levelling the failing key and my F is back fine. I had to screw-in about half a turn which looks rather much. I wonder what had happened. If anybody knows or has any idea please post.

Sometimes the adjusting screws are rather loose & self adjust. If this is the case I suggest putting a small amount of nail varnish on the head of the screw - take care that it doesn't go anywhere else or you might find things seizing up. Another possibility is that the small plastic silencer tip of the screw has fallen out.

Thanks, the screw is not loose, but I have to check the plastic tip as the problem appeared suddenly. In any case your comment has been very helpful, thank you