9100B with smoked zener

[Richard.Wilder]

Thanks Tony & Bushcat,

Here's where Vcol goes. It's the array of transistors that are part of the multi-layer ROM board.
That voltage doesn't appear on board 12 plug 1. It provides the voltage & current to drive the columns and for design purposes needs to be something less than -15 volts.

For some reason I can't attach pictures.
Look on the Tony Duel schematic labeled "Address Drivers 09100-66567" for the references to Vcol.