The Diag Board represents the ultimate realization of the test link concept. It doesn't just check RAM; it systematically tests:
The test program will guide you through a series of tests, providing you with a detailed report of your machine's performance. zx spectrum test program link
A message like ROM CRC error: expected 0x12AB, got 0x44FF means your ROM chip (usually a 2364 or 27128) has a bit-rot or a failed address line. Replace the EPROM. The Diag Board represents the ultimate realization of