In a grand action, achieving rapid repetition, with power and consistency, requires all parts to be in good condition and very precisely regulated. However, there are times when, despite seeming perfection and re-regulation, repetition fails and a key continually "locks up." The source of this particular problem usually lies in the jack stop / regulating button. In this case, the threaded shaft attached to the regulating button is very slightly loose in its hole in the jack itself, and consequently the jack is constantly shifting position under the knuckle during play. Just a small application of red CA glue will solidify the thread in the jack hole, thereby maintaining the correct jack / knuckle relationship and ensuring optimal response.

When a bridge cap separates from the bridge and there is a big space, even with the strings still up to tension, this is certainly a serious problem. The first thing to do is to get a mirror and a flashlight (or a combination mirror/flashlight tool, sold at piano supply stores). Check behind the piano (for uprights) on the inside of the posts to see if the nose bolts are coming loose. It's possible that you'll see a split in the wood, right where the nose bolt goes into the post. If this is the case, your plate is not down far enough, and you will have to shore up the nose bolts. You will need to loosen all the strings in the piano. When the strings are all loose you should notice that the the nose bolts that were stripped now are part of the way out. This proves that the plate wasn't all the way down, and you can proceed with the repair. Your next step is to take out anything in the way of the bolts and then remove them. Drill holes from the plate side, all the way through the post. From a good hardware store, purchase some large bolts and big nuts with sharp edges that can get countersunk into the post. Make sure the bolts have the same size head as the original nose bolts. Tighten them down well, so the nuts sink into the posts, then loosen them and re-tighten them, so they are just tight enough to hold the plate right where it is. Repair all the bridge problems, tighten up all the strings, lift all your coils,etc., and the piano should be fine.