Step 3: Cannibalize the PS2 Controller: Remove the Mechanical Switches
The main control board is also host to the mechanical switches that allow the strum bar to work.
On the back side of it, you will see two prominent black boxes, with white switches that will produce a distinctive *click* when they are depressed.
These are what we want. That click is the sound of the switch making contact, and it is the reason so many people prefer the GH controller. Not just the sound, which is a matter of controversy, but the reliability of the mechanism.
Using the same method you used to remove the ribbon cable, solder the BACK side of the contact points for the switches, while tugging gently on the switch itself. each time the solder becomes liquid, the switch should come a little bit looser. Alternate back and for the between the two contact points.
Once both of them are liberated from their circuit board prison, set them aside safely.
You can now discard the gutted remains of the Ps2 controller. Go ahead, they aren't doing anyone any good, any more.