@BigBodZod
Was it a socket 3, 486 Amptron? It is not a typical COAST module. This 486 M919 uses Asynchronous SRAM, same as the DIP-28 style pieces found on other socketed 486 motherboards. I have tried half a dozen COAST modules, neither work, though they fit in the slot. You need the 'special' M919 module. Pipeline burst modules will not work.
The SRAM chips on the module are the same as that of the skinny DIP-28, but of a different package. 8 pieces, 28 pins each, 1 tag. I may have seen this style of SRAM package still in production recently when searching on newark for a project at work.
I'd be curious if anyone has had any luck with this. I'm putting it on my hobbyist to-do list, though it is of lower priority. What I don't quite understand is that if the motherboard supports 256, 512, 1024 KB cache modules, why aren't there jumper settings for these? Could it be that the BIOS can auto detect the amount of cache? I've never seen that on a 486.
@SquallStrife
You can sometimes fix acid death motherboards by rewiring the PCB traces.