Coupler Mechanisms

I am not a fan of couplers, which are mechanical systems which couple a key to another key an octave below of above the key. This depends on the type of harmonium, but most instruments, particularly the collapsible style from Bhava and Bina couple to a key one octave above. If your hamonium has a coupler, there will be a lever on the far right side past the keyboard. Pushing the lever forward engages the coupler and pulling it back disengages it. 

When you press a lower key with the coupler engaged, the key presses down on a metal rod under the key. The causes the rod, which runs under the keyboard at an angle to the key an octave above it, to rotate forward. At the higher key, a smaller lever presses down on a wooden tab on the bottom of the key, which causes it to go down just enough to allow the reeds to sound, 

While you get a fuller sound with more reeds playing, the mechanism can create clicks when played. Also, and this is the worst part, if a key is lifted too far for some reason, the tab on the key which allows the rod to pull down the key ends up below the tab instead of above it, preventing the key from being pressed at all.

The picture below shows the coupler parts underneath the keyboard with the front trim board removed. The bottoms of the keys are at the top of this picture. 

Coupler Parts
Hook Tool

Remove Hinge Screws

This video from Nic at Old Delhi Music shows how to remove a coupler. 

Once the hinge screws are removed (see picture above) you can usually pull the whole coupler mechanism out towards you. Frankly, I don’t remove all the keys. At the 3:30 mark in the video he shows a piece that needs to be unscrewed. Just remove the keys in that area and you can expose the screw and remove it. It’s just about in the center of the keyboard.