ramps 1.4 d8 heater bed turns on when power plugged in (1 reply)

Hello
I have a ramps 1.4 running marlin
I recently ran out of pla and am now getting printer ready for abs.

I have a 18 amp computer power supply and all my motors extruder etc are working.
When I plug in the power to the ramps board AND the usb is connected to the computer the d8 heater bed pin stays on. In pronterface it says its off. The thermister is working fine.

I tried switching pins with the fan in firmware. no luck
I flashed sprinter No luck

I read it could be a mosfet. How would I check this?

Anything else I should check?

thanks
bryan