The original ULA has an unfortunate history of being prone to spectacularly overheat and fail without warning, leaving an unsightly crater in the Interface 1 plastic case. Because of this, and due to the original ULA now becoming hard to find, the vLA1 project was born.

The vLA1 is a pin-for-pin functional replacement for the Sinclair ZX Interface 1 ULA using a modern programmable logic array. The original ULA functionality has been reverse engineered and is replicated in full. The vLA1 provides full support for the Microdrive, RS-232 and Sinclair Network as in the original ULA.

The vLA1 comes in a 40 pin DIL package suitable for soldering into the Interface 1 PCB.
A word of caution, however, due to a lack of room within the Interface 1 case, the original ULA will need to be desoldered and the vLA1 installed in its place. There is simply not enough room for a socket. Have a look through the install guide (https://vdrivezx.com/vla1-sinclair-interface-1-ula-replacement) and you should get a good idea of what's involved.

vLA1 - Sinclair ZX Interface 1 ULA Replacement