U13 (74ls240) , U14 (74ls374) and U18 (LM339) are all in the Playfield switch logic as well. U16 and U17 are for direct switches not in the matrix (coin chute etc) . Also check the diodes in d3-d14. If you haven't already reference the schematics on http://ipdb.org if you don't have a copy. Do we know that it worked properly before the acid damage occurred?

These solder traces are very fragile in these games and are easily broken. You could start ohming out from the connector back to the chips to check for continuity. Here is the section of CPU you are looking at in the schematics. http://mirror2.ipdb.org/files/966/Williams_1990_Funhouse_Operations_Manual_November_1990_includes_low_res_schematics.pdf Page 112

You can't tell what's going on in the chip but you can measure each leg to it's destination to make sure the trace is intact. The chip's pin numbers are labeled on each chip in the diagram so you just have to use your ohm meter to check them. For example U18D Pin 13 goes to U13B Pin 11, should be 0 ohms or close to it. U18D pin 11 goes to R51 should be 0 ohms on one side 1K on the other from there it goes to the diode D3 and then to the connector pins. Some of the chip designations have secondary letters just ignore, eg U18A is still U18.

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It's likely still U19 / U20 , this is why you have to follow the traces. Likely one of them was eaten by the battery leakage and or damged while replacing the chip.

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