B&F Enterprises "Digital Clock" flakes out

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7 years 4 months ago #4850 by Jeff
I get all misty when I look at the hand tape-up artwork someone produced so very long ago. :)

Dr. Optigan wrote:

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7 years 4 months ago #4851 by wise65vw
Interestingly,the clock appears to share the last 7490 for both hours digits. The 7410 I'm assuming is for the 12-1 transition like on the Texas Instruments design. The other gates are probably used for controlling the tens of hours and the reset on the last 7490. It also looks like this clock uses transistors to take the incoming 60hz signal and convert it to a squarewave pulse. Not sure how good that would be with line noise.

The smoke means its working

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7 years 4 months ago - 7 years 4 months ago #4852 by Dr. Optigan
Yet another update:

After letting the board dry, I plugged the clock in, and it worked on the first try. It has been running fine for over 15 hours now. Still not ready to call it cured, but things seem to be looking up. :) *KNOCK ON WOOD*

(wish there was an easier way to do multi-quote)

Ty_Eeberfest wrote: Yep, I recognize the design. See the attachments on Post #1 and Post #7 of this thread:

www.tubeclockdb.com/forum/Builders-Forum...e-clock-problem.html

May not be an exact copy but it's really damn close.


Yeah, I definitely see the similarities. Any idea about the history of this design? Guessing TI had a hand in it, given the diagram in post 7, but the differences make me wonder.

Jeff wrote: I get all misty when I look at the hand tape-up artwork someone produced so very long ago. :)


Yeah, it's an interesting board design. A shame it wasn't made very well, and whoever worked on it didn't do a very good job with their soldering. I can't help but wonder what the "R" and "S" DIP IC pad sets are meant for; they look the exact same on both sides of the board, and don't lead anywhere.

wise65vw wrote: Interestingly,the clock appears to share the last 7490 for both hours digits. The 7410 I'm assuming is for the 12-1 transition like on the Texas Instruments design. The other gates are probably used for controlling the tens of hours and the reset on the last 7490. It also looks like this clock uses transistors to take the incoming 60hz signal and convert it to a squarewave pulse. Not sure how good that would be with line noise.


Well, in this case, either 12-1, or 23-00, I'd think. No idea exactly how they designed it to be 12/24 hour switchable, but they did. Also not sure how to switch between the two, but since I like military time, I'm glad it was set up like that.

Could line noise have caused the issue it was having? My guess is that a sync issue would just cause the time count to stop, but I have no real idea. Given that it was skipping ahead minutes or hours at a time, could line noise have done something like that?

Also, do the diodes involved with the sync circuit have to be of a specific type? One of them seemed to test bad, so my friend replaced it with a 1N4148 or similar. Does it have to be a zener, or something? Could the wrong type of diode being there have something to do with the glitching issue? Once again, thanks!
-Adam
Last edit: 7 years 4 months ago by Dr. Optigan.

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7 years 4 months ago #4853 by wise65vw
It'd be easier to know if I could see where the diodes are. If they come right off the 60hz output, usually a Zener is used to help square up the output. However, I have seen some methods where two diodes can be used instead of one zener, used to limit the max and minimum signal level to help "snap" the signal to a certain state.One connects to a 5v source at its cathode, and the other diode's anode connects to ground. The signal passes through the middle of them, the point where the anode of the first connects to the cathode of the other and is either pulled to ground or to 5v. They also help with line noise.

The smoke means its working

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7 years 4 months ago #4854 by Dr. Optigan

wise65vw wrote: It'd be easier to know if I could see where the diodes are. If they come right off the 60hz output, usually a Zener is used to help square up the output. However, I have seen some methods where two diodes can be used instead of one zener, used to limit the max and minimum signal level to help "snap" the signal to a certain state.One connects to a 5v source at its cathode, and the other diode's anode connects to ground. The signal passes through the middle of them, the point where the anode of the first connects to the cathode of the other and is either pulled to ground or to 5v. They also help with line noise.


The diodes in question are down at the 'bottom' of the circuit board, underneath the round bridge rectifier. The one at the top (which doesn't show up too well in my photos, unfortunately) is original, the one below it is either a 1N914, or a 1N4148. I don't remember the original diode having any markings; when tested with the diode checker portion of a Fluke multimeter, it gave readings in both directions rather than just one.
-Adam

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7 years 4 months ago #4855 by wise65vw
I don't mean to be condescending, but is there a chance the diode was put in backwards? Just a thought.

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