Accordions have 120 bass buttons, displayed in six rows of 20. Attached to each button inside the accordion is a rod that controls banks of other rods, which in turn control bass chords. A common problem with accordion bass buttons is they sometimes get stuck and lose their springiness, becoming trapped in the wrong position. You can remedy this problem by reconditioning the inside rods. This requires opening the accordion and removing the bellows from the bass housing.
Unscrew the strap and move it out of the way. Pull out the pins holding the bellows to the side of the accordion containing the bass buttons. Grab the top of the pin with needle nose pliers and pull straight out. Keep track of where each pin goes according to how long it is. Place it in a small container for safekeeping; there are usually six to eight of these pins. Remove the bass housing and lay it down.
Vacuum out any dust and debris from the bass housing with a long vacuum cleaner crevice nozzle. Check that there are no obvious broken pieces inside. Vacuum the bellows while it is apart if you like, taking care not to touch the delicate bass reeds inside.
Locate the rod retainer along the bottom of the bass housing. Unscrew the four small screws, two on each side of the retainer. Remove the retainer and take out the first row of twenty rods. Take out each row, one at a time. Pull the hook at the bottom of the rod out of the wooden damper. Pull the button at the top of the rod out of the bass housing. Wipe the rod with a clean cloth, spray with lubricating oil and wipe off any excess. Set the rod aside while keeping track of the sequence of rods as you take them out. Return the rods in the same order -- an absolute must -- when the procedure is finished.
Move on to the second row of rods, taking out the four screws from the second row retainer. Take out each rod and wipe, oil, then remove any excess. Keep track of the sequence of rods as you remove them. Continue until the second row of bass buttons is empty. Repeat this process for each row of buttons until all have been cleaned and oiled.
Replace each button first by hooking the bottom of the rod into the wooden damper, then pushing the button at the top of the rod back into the hole in the bass housing. Return all rods in the same order you removed them. Screw the retainer screws back in on either side. Press the bass buttons when all buttons have been returned in their proper order. Check that the smooth, springy action has been restored. Reattach the bellows and push in the pins with your fingers. Screw the strap back into place.
After all the rods are taken out in the first row, that row of bass buttons is empty in the housing. Compress the bellows without pressing any keys or buttons. If the accordion makes a sound, there is a stuck rod inside.
Avoid touching the bass reeds in the bellows when vacuuming that area with the crevice nozzle. The reeds are delicate and can easily be knocked out of tune.