KSR6 - M2 not working

It’s the first electronic montage of my 15 years son. I checked all I can do with my basic electronic knowlegdge.
He has reversed the transistors Q1, Q4 and Q6. But even after the correct montage M2 doesn’t want to work. Perhaps the inversion destroyed something ?

I just have a multimeter. What can I test ? My son is very disappointed for his first experience :frowning:

Thanks for your help.