14-10-2020, 11:36 AM
The 74xx151 is either IC3 or IC4 depending upon the microbee mainboard model.
As for the resistor network, this value can be tuned according to your circumstance - e.g. low resistance or high resistance key switches.
These tunings are bodges made to accommodate the high resistance switches.
Even with brand new sealed bag old stock keyswitches have developed the unwanted high resistance.
It's probably due to the chemistry used for the carbon pills.
It's performance being not dissimilar to the fault stolen electrolyte formula for electrolytic capacitors.
As for the resistor network, this value can be tuned according to your circumstance - e.g. low resistance or high resistance key switches.
These tunings are bodges made to accommodate the high resistance switches.
Even with brand new sealed bag old stock keyswitches have developed the unwanted high resistance.
It's probably due to the chemistry used for the carbon pills.
It's performance being not dissimilar to the fault stolen electrolyte formula for electrolytic capacitors.