For the initial 12v supply I'm using a repurposed computer power supply, so I think that part's ok as far as output level and being ripple free. The board's regulator doesn't heat up noticeably and it feeds something around 4.9 to 5v to the other stages. That voltage level is also present at all the other 5v feeds across the circuit. I forgot to say in the first message that U4's voltages are all on spec per the instructions. 'Tis a puzzlement, as Yul Brynner said.
Thank you for the quick reply, Ken!
