Got the polarity of the *Input Select* line on U70 and U500 wrong.  This line is used to select either the output of the internal one-shot in the LM1815 or and external timing pulse.  Had it selecting the external pulse which didn't do much good at all. U70 wasn't too bad to fix because the trace to pin 11 was on the bottom side of the board.  But of coarse U500 had it on the top under the IC.