Yamaha SY99 Key repair
This is a small guide to replacing keys or key springs on a Yamaha SY99. I will add pictures later. DX7 keys should fit just fine although you may need to file down one pin in order for them not to hit the chassis board. The springs appear to be the same in the SY99 and DX7.
In order to get to the keyboard of the SY99 it is NOT necessary to remove any of the printed circuit boards. I’ve seen statements on numerous websites about having to basically disassemble the entire SY99 in order to get to the keys and it is simply not true. That only applies to repairs to the LCD screen.
First my key wasnt moving properly (it felt heavier than the rest of my keyboard. Then finally the spring gave away and my key dropped down never to get up again so the keyboard became unplayable. Quite annoying indeed. Luckily the fix was a thousand times easier than I expected. As it turns out the spring wasnt properly socketed and had moved and jumped out of its position.
Here’s how I fixed the broken/moved spring on my SY99′s center A key.
1) unplug the SY99
2) turn the SY99 upside-down on a soft surface. I used my couch 
3) remove all the screws on the bottom except for the ones inside the rubber feet. write down which screws came from where. I noticed that in the center where the screws sit in some lowered areas, these were slightly longer than the others. Mark those properly.
4) take the bottom cover off by tilting it slightly towards the keyboard side and moving it towards you (SY99 with the keys facing your way)
5) You should now see some circuit boards and the bottom part of the keyboard assembly
6) Note that the keyboard has two big IDE like flatcables running towards it. They end up on one connector on the main circuit board. remove that connector by gently tugging it from the board. No need to write stuff down here, the plug only works in one direction
7) remove the larger connectoron the small circuit board on the left side of the keyboard assembly (likely the aftertouch controller). Make sure you take the big one out. Not the small one. be careful near the small flat ribbon cable as it is easily damaged.
remove the two large black screws on the left side next to the printed circuit board that hold the assembly to the main enclosure
9) do the same on the right side. You will notice that each side has a hole that fits onto a small protruding plastic pin.
10) remove ALL the copper colored small screws IN FRONT OF the printed circuit boards including those hiding under the keyboard assembly’s main flatcable. you ONLY remove these screws and do not touch any screws on any of the printed circuit boards.
11) check to see if you als took out the copper colored screws (4 I believe) that hold the aluminum foil shield onto the keyboard assembly (left side)
12) you should now be able to carefully lift the keyboard assembly from the enclosure. In order to do so you will need to rotate the front side of the keyboard assembly slightly upwards towards you and lift the two aluminum rails on the side in such a way that they unlock from the two protruding pins. You may need to slightly bend the metal part of the left side cheek outwards carefully to do so.
13) Woohoo your keyboard is now fully removed from the SY99 enclosure without messing with any electronics
14) turn the keyboard chassis right side up and you will notice that there is a white plastic strip clamped down on the entire ridge of the back of the assembly. This plastic strip keeps the keys from coming loose from the main chassis. Carefully lift it and peel it off the edge. Be careful not to break it.
15) You can now remove any of the white keys by carefully pushing it backwards and then lifting it from the chassis
17) you will notice that there is a metal lead spring inside the key. The notched end of the spring goes INTO the key and fits snugly into the protruding pin while the other side precisely fits into a small notch on the other protruding pin on the key. The spring will be fitted diagonally. If you hold the key upside down it will look like this: _F__|/|_ where the / is the spring.
18) carefully slide the key into the chassis and make sure the spring falls into the socket on the chassis while doing so. Push the key towards the rear a little more and it should snap into place.
19) I have noticed that the DX7 key springs are the exact same as the SY99′s so you should have no problem finding replacements. However I did notice that the A key of the DX7 has an extra protruding pin on one side that will prevent it from fitting into the SY99. In the end I stuck with the original key because it appeard that only my spring was messed up and the key itself was ok. If you want to use the DX7 key instead, you can simply file off the extra “pin” on the side of the key and it should fit without any problems.
20) assembly is the same thing but the other way around. The whole thing took me about 20-30 minutes.
21) If you have aftertouch issues after assembling everything again, check the small flat ribbon cable on the left side of the keyboard and make sure its fitted properly into its socket.
So there you go. Simple SY99 keyboard disassembly without having to remove all the other stuff inside the enclosure
