Not able to power on - get fan spin with SMC bypass

Machine was unable to power on. I tried an SMC reset, and the charger light changed so I know it went through and that the power button works, but the machine still couldn’t power on. I tried a separate battery that was known to work and had some charge on it, and I still wasn’t able to power on.

I confirmed the MagSafe 2 board was passing the correct voltage. I even took the machine to a sort of minimal configuration by disconnecting components from the logic board. At no point would it power on. I eventually tried an SMC bypass and this caused the fan to spin but there were no other signs of life (no data on display, CAPS lock key didn’t light).

Also there are no signs of corrosion on the logic board or other components. Anyway, I’m just wondering what other steps I can take! Thank you.