First you must remove all chips that are socketed and in inspect all the legs and body for corrosion. If corrosion is present remove that corrosion. You need to completely douse the logic board using 91%-92% IPA (in your case, maybe a short submerge for a few hours may be a better bet since that is some seriously evil corrosion...) and then scour your logic board with a soft tooth brush (the softer the better) using a Sonicare or Oral-B on its lowest setting, and scrub until the sensor comes on that you are brushing too hard. back off, scrub all of the visible gunk, and every and kook and cranny, Then dry blow every inch of that logic boarb, using the COOL settimg.(This Is CRITICAL) on a blower dryer, especially the large chips. Once you are satisfied the board is dry, let it it sit for 72 hours for all the residual moisture to evaporate . And hopefully you are good to go.
I have used this method many times, without fail, so I feel confident it will restore a logic board to working order, at least temporarily, until more permanent pairs can be completed. This is assuming that the underlying problem is mild-to moderate cap rot. If anything else is going on this method most likely will not work. All though it will not makes things worse, one must always remove cap goo as the first step to repair