Thanks to everyone for their input.
I did get one of them going last night. I retouched the connections for the 10 ohm mod and it sprang to life.
The other one is one that I built back in 2017 that never worked from day one and it is now a parts donor as I have screwed up a few traces desoldering and resoldering etc.
I will just buy another to replace it. I really like these little units. They really do well with the U3S.