The system will run without U177.
If the leakage was bad, it may have affected U891 which may have damaged the memory interface. The system will not boot without chip memory.
There are 3 tracks which run through the real time clock area, these commonly get corroded open circuit and may cause booting problems.
Time to start checking tracks and vias in the corroded area for being open circuit.
I've written various technical guides on this kind of thing, most aimed directly at the A4000D:
http://amiga.serveftp.net/hardware_repair.htmlI can also supply the correct replacement part for U177 ex stock if required.
Non booting can be tricky to solve without the right test equipment and knowledge. Email me if you need some more help.
