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Neutrino · 12th Oct 2021, 9:38 am

I assume that the decoupling capacitors are hidden on the back of the Veroboard.

I think that a fast edge, such as produced by SN74LS14 inverters with Schmitt-Trigger inputs, is needed to ensure that the flip-flops in the decade counter are clocked simultaneously, especially with the input applied to CKB to get a symmetrical output at QA.

I would have used a lower voltage Zener diode to ensure that the input voltage cannot exceed the supply voltage.

David

12th Oct 2021, 9:38 am	#2
Neutrino Pentode Join Date: Oct 2016 Location: Maldon, Essex, UK. Posts: 184	Re: Interesting Vintage TTL Logic IC Problem I assume that the decoupling capacitors are hidden on the back of the Veroboard. I think that a fast edge, such as produced by SN74LS14 inverters with Schmitt-Trigger inputs, is needed to ensure that the flip-flops in the decade counter are clocked simultaneously, especially with the input applied to CKB to get a symmetrical output at QA. I would have used a lower voltage Zener diode to ensure that the input voltage cannot exceed the supply voltage. David