The story begins here 486 motherboard L2 cache misconfigured on purpose?
I found that the actual cache size is 64KB, while the motherboard has soldered SRAM chips that should give 256KB of cache, and the bios was altered to misreport cache size as 256KB.

I've finally received the Renesas chips I've ordered from Mouser, so it's time to fix this issue.

First removing the fake chips. I don't have any sophisticated equipment (no fancy vacuum pump soldering iron), so I've preheated the relevant part of the motherboard with spare heating bed from 3D printer, then used hot air gun to heat the pins, chip by chip. When solder has melted, a slight knock on the mobo - and the chip falls out under its own weight. Idea was to not apply any force to avoid tearing/lifting the traces.

Desoldered chips, both sides:

It went very well and quite easy. The pads are in great condition, nothing damaged, no tears or burns.

The silkscreen labels suggests the board expects Cypress CY7C185 (8K) or CY7C199 (32K).