I have a system 6a mpu on the bench. As far as Leon’s test rom goes it is working and passes all tests including the memory test.
I can also test all outputs when I add a known good driver board.
However when I put Flash roms in to test it in my machine I get a double flash on boot with no displays and the blanking signal stays low. The other signal that is missing is the A9 address line.
Those signals are good with the Leon test rom.
I have seen a few mentions of this double flash but usually the reference is to pressing the test button which indicates that it passes the self test.
I am not really sure what this double flash on boot is telling me, can anyone give me a bit more info.

I have replaced all the usual sockets and also continuity tested them all. Also swopped roms, rams, Pia and cpu. The blanking circuit has been rebuilt but it works ok with Leon’s test.

Thanks for the reply. I have read and do use that document but it doesn’t tell me about the double flash on boot.
I have resolved my issue by using a couple of the pincoder test roms.
Rom 8 is the irq test and my board was failing that. After following the guide and swopping ic 5,11,25 it ended up being the 6808 cpu at fault.
I was thrown a bit as it passed Leon’s tests.
New 6808 and the board is running fine.