Ps2 controller buttons not working (Circle and Triangle)

The ribbon cable that reads all of the button inputs is pretty fragile and degrades over time. You might need to replace it with a new one; they usually only go for a dollar or two each on ebay.

You will first need to take your controller apart and check if the connector has A) 18 or 19 pins, and B) a removable or attached cable. You can find the Dualshock disassembly guide here:

DualShock 2 Disassembly

Mine had 19 and was attached:

If it’s removable, it’s a super easy drop in replacement and you won’t need to replace the connector. If not, you’ll need some soldering skills to remove the connector and replace it with a new one. The connectors usually ship with the cables but make sure before you buy. Once you do this the cable will now be removable, so if it ever degrades again it will be easy to replace.