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paranormal activity of CMOS IC

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vinodquilon

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Look at two attachments...

In the circuit 4017 doesn't like its home place.

When I changed its place from circuit IC socket to a breadboard and fed its input &
supply directly from corresponding IC socket in PCB (by tapping upper socket pins through
simple wire strips) ,I got output at pin 1.

But when I return IC back to PCB socket from breadboard, I didn't get output at pin1!!!


I am sure there would be no problems with IC and socket. Also all inputs to 4017 was correctly
there.

Does there exist any interferences from neighboring components as 4017 is a CMOS IC ?
 

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    4017 copy.jpg
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Someone says it is due to 'cold solder joints'.
Some others care about 'missing of bypassing of supplies'.
Others are interested in 'floating inputs'.
I think by clearing all the above three cases, my problem would be solved. Thanks...
 
Another issue is mixed use of LS TTL and CMOS devices

why don't you replace the 74LS123 by a compatible device in CMOS?
while a logic1 is almost5V in CMOS, it is any thing above 2V to 2.4V(never 5V) under LS TTL.
As such a cmos might drive a TTL but a TTL may not drive CMOS
here we may also use level translator

you may check whether CD4528 works for your needs.
 
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Definitely check the inputs. even with an unused portion of the chip, floating inputs have caused strange problems with some of my circuits in the past.
 
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