Certain new Kohler & Campbell grand pianos, especially those models manufactured in Indonesia, have a peculiar recurrent problem --- bichord bass dampers which do not dampen. They may appear to be properly seated, with proper lift and timing, but the strings continually sing nonetheless, and re-regulation of the damper heads will fail to correct the problem. Only a comprehensive and complete inspection and adjustment of the entire pedal and damper system will succeed in achieving proper damping.
1. The first thing that must be done is to drop the lyre and open the pedalbox. The three pedals all pivot on one continuous pin, and the machine screws which hold the top mounting plates down are always overtightened by impact tools. This causes the sustain pedal to bind, and not return to full rest position due to excessive friction.(thus keeping the damper tray slightly lifted, and the dampers off the strings). Remove the top plates (which can be very difficult) and the pedals, and lubricate the long pedal pin with MPL solid. Re-install the pedals (making certain that the bushing cloth does not bunch or curl, and remains in proper position around the pin and under the pedals) and screw the mounting plates back onto the assembly. Tighten firmly only by hand. The sustain pedal should now move very freely and smoothly, easily returning to full rest by the force of the trap spring.
2. With the now responsive sustain pedal, check for sufficient lost motion of the damper tray. An adequate gap between the tray and the capstans under the damper levers is desirable so that no levers are in contact with the tray when at rest. If an adjustment is needed, turn the cap and lock nuts on the pedal rod to raise or lower the tray position. Adjust any capstans that might be too low and still contact the rail. The design of these damper levers also uses spoons which are raised by the key-tail felts. Check that all spoons are in a straight line and at a sufficient height above the key-tails so that none are being slightly lifted when at rest through direct contact with the key-tail felt.
3. It seems that many of the agraffes on these pianos have poorly drilled holes which are not at identical heights, thereby creating the problem of singing strings. With the pedal at rest, pluck the bichord bass strings with your fingernail or a plectrum to locate any singing strings, and with a string hook, pull up firmly on any offenders.

Square grand aren't too difficult to work on once you understand the procedure. First figure out how to take it apart and what you are going to do to it. It is more difficult to change the hammers, but it can be done. The set I got I believe was from Ronsen. When they require only filing, it is easier.

The spring system in the square grand isn't made to last over a hundred years. It can be converted to an upright jack spring system fairly easily. Drill a hole in the spot where you think you would put a jack spring. That hole you drill will break out the old spring system. Pull out the old spring and string from the other side with a thin tool or small tweezers. Make sure the hole you drill is the size of the jack spring. The jack should just slide in half way. You will have to put an awl mark first, then a smaller hole, so you don't crack the wood. You also will have to put a little notch in the jack, so the top of the spring stays in the spot. All the other things in square grand regulation can be figured out fairly easily if you look it over carefully. The only difficult adjustment is the rocker capstans. Make sure they are tight or else they will click.

It is a good idea to take on odd jobs like this if you have the time and the customer is willing to pay you for it, because the experience you get will help you in the future. I especially recommend for young technicians who have extra time on their hands to try these kinds of things. The best technicians have the ability to figure things out, think up new tricks and design things in different ways (thinking outside the box), and make new parts if needed.