[sdiy] TR-606 last step not working

[nathan at idmclassics.net]

I've got a 606 here where almost everything works fine - except that when
the function button is held down, it's associated functions do not work. 
 
For example, during pattern write mode while the pattern is running,
holding down the function button shifts the LEDs to their appropriate state
(displaying the quarter notes on 1/5/9/13), but then hitting a step to set
'last step' or changing the scale before holding down the function button,
has no effect. It won't change away from a last step of 13. I have not
tried the function button's functions during song write mode.  
 
All steps work fine in write and pattern select modes. While I've got the
606 plugged in it remembers patterns between power cycles, so it appears
that the memory is fine. All of the wiring between the button board and
main board is fine. 
 
I had received this with some components in the power supply blown which
have since been replaced. 
 
If anyone has an idea of what might be going on it would be greatly
appreciated. Thanks. 
 
- NT