Finally got Frogger sound working !!!
There are many small differences between Scramble and Frogger boards – mainly address pin swaps, but there are a few hard to find ones. In Scramble one of the AY3-8910 sound chips uses bits 7,6,5 & 4 as inputs, but in Frogger it’s bits 7,6, *3* & 4. “5” and “3” look really similar on the old hand drawn schematic.
I should have looked in the MAME driver more carefully, they found it 🙂