USB devices not working - bad logic board?

I have 3 macbooks with various degrees of liquid damage. 2 are a question for another day. Each was "spilled" on quite some time ago; maybe as long as a year.

Wives and daughters and macbooks don't mix.

The one I'm interested in is a MBP 13 inch unibody early 2011.

Started by reading your liquid spill/cleanup guide.

Took the machine apart - removed the logic board - cleaned any and all signs of corrosion with isopropyl - dried and reassembled.

Machine powers on, boots up, loads OS. But I can't go further because internal keyboard and trackpad are not working.

Now we get down to my question. An external USB keyboard and/or mouse do NOT work either. I can replace the internal keyboard relatively cheaply ($25 on Amazon) - but - is the fact that the external USB devices are NOT working a sign there's probably some wrong with the logic board?

It's a no-brainer to throw $25 bucks at it for a fix - but a new logic board will run me 10x that. Not sure it's worth it in that case.

Thanks!