Then it's a board problem for sure. You need to clean the remaining corrosion (pretty much broadly the area between the power connector and the PCMCIA enclosure. I again recommend foaming Scrubbing Bubbles if that exists in Austria. That's what brought my board back to life. But techknight may be right - the vias may be rotted out.
Well... remove the corrosion and see what happens. If the vias or traces are bad then that poses a bigger problem. But again - my board did not originally have video, and washing it -scrubbing bubbles and eventually the dish washer- well ultimately fixed taht.
Is there a size cap on uploading photos? It's not a big deal it's just somewhat awkward to keep downloading.
Also, your board's main damage is surprisingly far to the right. I've pointed out (above) some damage farther left, but just keep in mind that whole area (like the upper left quarter) probably needs to be clean.
I got a new PowerBook 3400c/200 (my second) - the Kanga must wait some more days, as it has more bugs.
So the 3400c was said to have a buggy keyboard, nearly all keys don't work...
The truth was, the PRAM battery leaked and dripped down around the keyboard connections. So I disassembled the whole PB, additionally repairing some different bugs (missing rear feet and feet housing etc.).
Then I carefully cleaned the board, keyboard connectors and flex cables. After that the keyboard worked 90 percent. So I swapped it with a 5300 keyboard and now only 3 rightmost keys don't work.