I managed to find a jumper on a 15 years old PC of a friend,
but that did not resolve the problem either. The RAM in A1 and A2 works just fine, whenever I add RAM to B1, B2 or both I only get the 3 beeps when trying to start. The RAM is tested and ok, I think it is highly unlikely that the CPU is working with channel A but not channel B so I guess it is most likely that the board is not ok. Anyone got any other ideas? Else I just return the board I guess.