Spectrum Computing

Hello! I am not sure if I am posting this in the right place on this forum, I wouldn't mind being moved in the correct place. (i.e. the trash )

I am a writing this as a complete newbie with Spectrums' and electronics. I own a broken ZX Spectrum 48k Issue 6A. On the first look of the PCB, I noticed that a chip named PCF1306P (IC27), which was resting on a socket seems to be corroded. When I tried pulling the chip off carefully, some of the chip's legs fell off, and some of them got stuck in the socket. Obviously, this thing needs to be replaced. Both the chip and the socket.

I found someone who's selling a replacement of this chip on Ebay, but I'm still unsure what does this chip do. Can someone provide me with resources where I can inform myself, or ELI5?

Thank you!

P.S. Here are few pictures of the chip

IC27 is a custom glue-logic chip that was introduced in Issue 5 boards, replacing about six standard 74-series ICs and reducing the overall cost of production. They are no longer being manufactured (obviously), so your only options to source them are to either remove them from another Speccy, or to get a modern replacement that mimics their functionality using discrete logic, which is what your eBay seller seems to be offering.

IC27 (PCF1306P / ZX8401) multiplexes the Z80 sixteenth bit address lines into multiplexed address lines suitable for all the DRAM chips. Seven lines for the ‘lower’ DRAM chips and eight lines for the upper’ DRAM chips. It also produces the control signals for the ‘upper’ DRAM chips.

If IC27 has suffered from corrosion, it would be a good idea to carefully examine the whole board for further damage.

Mark