Amiga 4000 motherboard works from cold boot, then freezes after few minutes and shows green screen after reset. Cold boot (after about 5 minutes) would restore the board, then symptoms repeat. No corrosion in the battery area.
Solution: U212 controlling CAS/RAS is unusually hot, inputs are OK, but outputs show undefined “half” (pulling low from about 2.3V) levels. New GAL chip (22V10D-10) will solve the issue.