UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Mark1960 · 20th Jan 2022, 7:18 pm

Port D input mode is schmitt trigger with input levels of 0.2Vdd to 0.8Vdd, so would not be compatible with TTL input levels from the MK14. So Karen made these address outputs instead.

If the 887 is TTL level inputs on both B and D then I would agree with Sirius that there is no reason to swap them back, which would maybe allow the same pcb layout for both chips.

20th Jan 2022, 7:18 pm	#561
Mark1960 Octode Join Date: Mar 2020 Location: Kitchener, Ontario, Canada Posts: 1,298	Re: Ortonview PCB Port D input mode is schmitt trigger with input levels of 0.2Vdd to 0.8Vdd, so would not be compatible with TTL input levels from the MK14. So Karen made these address outputs instead. If the 887 is TTL level inputs on both B and D then I would agree with Sirius that there is no reason to swap them back, which would maybe allow the same pcb layout for both chips.