J9 is the CMOS reset jumper. The pins are probably not installed on the PCBA.
Not sure how to insert a picture here but, there’s a single aluminum electrolytic capacitor just to one side of the smaller heatsink on the component side of the board. In the space between the capacitor and the heatsink, is J9. It’s marked on the board.
You can solder a 2 pin header there, or better yet, a right-angle 2 pin header on the back of the board for easier access. Then just push a jumper onto the 2 pins and that will kill power to the cmos memory. For the soldering phobics, you can short the two pins with the tips of a pair of tweezers on the back of the board.
I don’t know the procedure, but I expect it follows a standard motherboard practice. I have some dim memory that you install the jumper, then power up and the bios sees that cmos lost power and checks the jumper state and then reinitializes cmos with default values. Remove the jumper, power down and back up. Sorry, I’m not a motherboard expert. I could be wrong.
Edit: I looked up the cmos reset procedure in the ICH9 spec and it appears that with the power completely disconnected from the unit, you put a jumper on jp9, leave it there for a few seconds, then remove it and then reconnect power to the unit.
You must completely disconnect power from the unit, not just that it’s “powered down”, as many of the internal supply voltages are still present as long as the power supply brick is connected to the DX4000.