This is something I started a long time ago but only got off the backburner recently. In a nutshell, it's a pair of diagnostic ROMs that's supposed to do a better job of error reporting. Ideally it ends up saving hours of trying to find the cause compared to what the original BIOS does for you. The other major thing is that it includes a Z80 ROM for an actual Z80 test instead of the really basic "Z80 ERROR" you might see. The Z80 part requires a spare CHA board (any one with NEO-ZMC), a socket and a 27c1001 to burn but it's optional. The BIOS just takes place of the regular BIOS but it can't be used to play games.

Enabling proper Z80 testing is the reason I started it since the original setup is almost worthless for that. It does have a full set of tests for the 68k end of things though. A lot of tests have been added and are more precise in reporting what actually appears to be wrong and are more likely to catch certain problems that the original tests can't. Another bonus is that it's more likely to give a meaningful info on a completely dead system since it doesn't rely on as many working components, so a system with the click of death is worth trying with something like this. There's a bunch of other things too but most of it on my site.

Here's the homepage with download links and some info. I tested this on my own AES+MV1T+MV2F+MV4F and it seems to work fine. Any suggestions or questions, just shoot. Even if you don't understand what an error is trying to tell you, just posting a pic of the results may help you save a lot of screwing around. I already got some use out of it with a 4 slot that I've been sitting on for a while and hopefully repairers or anyone with a load of systems can get some use out of it.