[sdiy] Issue with CD4024 Ripple Counter

[Tim Stinchcombe]

Hi David,

Well good progress indeed! This:

> Next, I built Tom Stinchcombe's test circuit on a breadboard and tested
that.
>  ...
> 
> Result: CD4024BCN clocked on the negative edges (correctly), and CD4024BE
> clocked on the positive edges (incorrectly).

and more lately this:

> I just tested CD4024BE and CD4024BCN on the breadboard, this time clocked
by
> a CD40106 hex Schmitt trigger.  The 40106 was powered with 15V (VDD) and
0V
> (VSS), and I used a 100k resistor and 100nF cap to create a square wave
oscillator
> with a frequency of about 120 Hz.  The output of this oscillator is a
perfect pulse
> wave that oscillates between 15V and 0V.
> 
> Results: No change.  CD4024BCN clocked normally.  CD4024BE clocked
> backwards.

are very conclusive evidence that it is the chips that are the problem and
not anything to do with your circuit.

(I was going to ask after the first posting what the rise/fall edge
timings/rates were, but driving them from the 40106 should ensure that they
are going to be well fast enough.)

> Conclusion:
> 
> These CD4024BE chips are defective.

So I broadly see just two possibilities:

  - they are damaged either through misuse or handling, or
  - they are fakes/counterfeits

That you have three exhibiting the same problem pretty much rules out the
first (though I recall an instance at work where we were fairly sure we had
a hole tube of about 25 ICs that all seemed to have suffered a similar fate,
possibly static damage or the like), thus the second would seem more likely
to me.

I have had a lot of practice at detecting fake chips over the years - I once
posted quite a lot of photos of examples I'd seen to a thread at MW if
anyone is interested - and so will volunteer to cast my eye over them and
offer up an opinion as to their legitimacy or not, but that will obviously
cost a little in postage across to the UK.

I too was going to suggest that your next move would be to source some more
TI CD4024BE parts, preferably not from the same source as the others unless
you really do feel that they can be trusted, and I certainly wouldn't accept
*any* that have the same batch code markings!

Contact me off-list for my address if you feel like posting them to me!
(Though it is likely you have it on an old email - I've not moved in all the
time I've been signed up here!)

Tim
__________________________________________________________
Tim Stinchcombe 

Cheltenham, Glos, UK
email: tim102 at timstinchcombe.co.uk
www.timstinchcombe.co.uk