How to start up the computer on the logic board

My computer was liquid damaged 6 months ago, and on service, they told me that the logic board had to be replaced. I didn't do it, and bought a new one. a couple of weeks ago, I tried to power on the old macbook, and it went on. the only problem was that when in os, it was like I pushed the power button, and the power off window in os pops up. If I don´t do anything, the machine just turns off, and I have to restart it. but after about 8 starts, it suddenly won´t turn on.

I talked to a technician at an apple workshop, and he told me it could be the power swith and told me that i should try to start it up by short curcuit two pins on the logic board. does anyone know where they are located? He tried to explain it to me, but it wasn´t easy, since I didn´t have the machine with me. Picture would be nice.

Thanks for the advise. this is the same problem, but my logic board is newer than the LB in the post, so the location of the pins is different.