Just wanted to update everyone on where we are at on this project. One of the first things that my friend Mike questioned was why are we using 74LS series instead of 7400. I have order new ICs for everything except the 141s. Here is the last update that I received from him.
Ok, did some quick calculations, and the drive current needed to drive the 7417 from the output of the counter with the 360 ohm resistor to VCC, you need 14ma. The current output of the 74LSxx counter is only 8ma, and the 74xx is 16ma. When and if the 7417 see's a good logic low on it's input, it's output will switch low pulling the 510 ohm low, 9ma needed, helping drive the counter output low. The 74LS17 can drive 30ma, so that can help once it can see a good logic low (.8V) on the input. So, if we increase the resistance of the 360 ohm resistor to 625 ohms, that may be a place to start. These are rough calculations, but I would go back to using the 74xx's instead of the 74LSxx's this would have been better. Mike On Tuesday, March 7, 2017 at 6:37:54 PM UTC-6, [email protected] wrote: > I'm hoping that someone out there can help me with a problem that I am > having with a Taylor Edge clock kit that I built. After completing the kit > and plugging it in it seemed to be working fine. Then I noticed that the > 10s second display tube and the 10s minute display tube were not counting > correctly. They would count from 2 to 3 to 4 to 5 but then it would go back > to 3 then 4 then back to 2 and then start the sequence over again. The 1s > second and 10s minute tubes would count fine. I asked a friend of mine that > knows a lot more about this stuff than I do and he recommended that I try > disconnecting resistors R13 and R15 (both 240 ohm) from the time setting > circuit to see what would happen. This fixed the counting problem but now I > cannot set the time. I can't believe that I am the only person that has had > this problem and am hoping someone out there knows the answer. I am > attaching the schematic. > > Thanks > Dave > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8f1bbc47-9661-4e52-9a19-54b21668a3a3%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
