New Build ZX Spectrum – Adding Lower and Upper RAM
The old Spectrum used two types of RAM. 4116 chips for the lower 16k of RAM and 4164 or 4532 DRAM for the 32K of Upper RAM. An interesting tidbit is that the upper RAM chips on the Spectrum are actually 64K, however only one half passed the manufacturing tests meaning only 32K is usable, and this significantly lowered the cost.
These chips haven’t been made for a very long time, and are usually one of the biggest failures on the original Spectrum so a modern replacement is a must, and luckily Retroleum have created modern replacements. https://www.retroleum.co.uk/zx-spectrum-chips
These are single chip boards, and slot in place of the old chip locations and are 100% compatible replacements.
If you can’t get these boards, then you can get hold of the 4116 and 4164 chips usually salvaged from old computers and use these instead, however beware a lot of sellers, especially from China sell fake chips, so make sure to test them using a chip tester. We use the wonderful Retro Chip Tester Pro but you can also make your own using an Arduino.