P Todd Decker via groups.io wrote:
Should all the LS chips be replaced with HC? And, if so, can the originally specified 47K resistor values be maintained?I haven't looked at the RC1802 schematic closely. But the diode OR gates in the original PE Elf used 47k pull-down resistors. Since they all drove CMOS inputs, it worked.
The problem comes because the N2/LOAD signal can't drive a 74LS input (much less 3 of them, as would happen if the PE Elf's IC10 was a 74LS10 instead of a 4023).
That makes me wonder: How does the RC1802 drive the TIL311 hex displays? The PE Elf used eight 4050 buffers to drive its display, because these are TTL parts. They would overload the bus without the buffers.
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