Hour of my digital clock skips

Thread Starter


Joined Jan 6, 2018
I have to come back at this topic because it was never resolved so please bear with me. The hour of my CMOS digital clock skips ahead when I unplug or plug in the the power in the wall or turn the fan on or off which uses the other of the dual outlet. When I put in a .1uf capacitor at the primary of the transformer the problem is resolved. I need to know how to resolve this by doing something to the secondary of the transformer because I can work on that in the clock because it's not safe to work with the primary and those where I live would probably say it's unsafe. so I need to do something to the DC end of the power supply and have included a schematic. When I unplug the DC power the battery backup works okay but when I unplug and plug in the primary of the transformer the hour skips ahead. I tried putting transient protection diodes across the rectified DC but it doesn't work. I have a small inductor that I tried after the rectified DC and that doesn't work either. I need to know what to do with the DC power supply so the hour does not skip ahead when there is a variation in the primary of the transformer. Maybe there's spikes in the primary but somehow getting into the secondary and doing something wrong to the clock. You all told me before to put bypass capacitors across the CMOS power pins on the ICS but I don't want to do that and I don't think that's the problem. battery backup.png
Last edited:


Joined Jun 19, 2012
The lack of a bypass capacitor on the output of the regulator is my first suspect.

You also MUST bypass every chip with a 0.1 uF cap, this is not optional - if you want things to actually work RELIABLY.
Place the caps as close as possible to EVERY Vdd and Vss pin.


Joined Apr 11, 2010
<rant>. I begin this rant by apologizing to noobies everywhere.

I don’t understand the following logic. When a thread starter tells us his problem and one or more members provide a solution, the conversation proceeds like this.

“My project (design, circuit, module, micro, etc) doesn’t work. I know you said to plug it in (add a diode, capacitor, resistor, filter circuit, etc), but I don’t want to do that!

::face palm::

Thread Starter


Joined Jan 6, 2018
I hear Sparks at the wall plug when I plug the transformer in the wall, could a common mode choke work if there are spikes and Sparks?