I got the main sequencer board soldered up. Powered it up and weird
things started happening. Output 3 permanantly on, output 4 never
turns on, and output seven is skipped (by skipped I mean it jumps
from out 6 to out 8 with not even a pause on 7). Thought what the...?
After much head scratching I decided to breadboard the circuit. Just
the 4017 and half the LM358. No reset or End Out circuitry. Fired it
up and this time I got nothing on output 2 and output 7 is still
skipped over. Hmm...I replaced the transistor (bad one) for output 2
and that problem was fixed. Tried different chips: seven different
Fairchild CD4017BCN all had the skipping output 7 problem. Out of ten
Motorola MC14017BCP five worked perfectly. Problem solved, now all 8
outputs work properly.
Out of 17 chips I only have five good ones? I found this hard to
believe, so I re-installed one of the bunk Fairchild chips and
started swapping out different LM358s. I tried Fairchild and National
brands, and also LM2904. No change. Then I tried a TL072. Fixed it!
Then I tried TL082, BA4558,MC33077. All worked. It seemed any split
supply opamp worked. With the LM358 replaced by a TL082, I started
swapping out 4017s. Every one of the seventeen 4017s I have worked
perfectly!
Can anyone explain this ? I'm just starting to dig into CMOS stuff
and this really threw me. A nice thing about this discovery is maybe
I can finally get my Gated Comparator working properly since it
exhibits the same kind of skipping behavior.
things started happening. Output 3 permanantly on, output 4 never
turns on, and output seven is skipped (by skipped I mean it jumps
from out 6 to out 8 with not even a pause on 7). Thought what the...?
After much head scratching I decided to breadboard the circuit. Just
the 4017 and half the LM358. No reset or End Out circuitry. Fired it
up and this time I got nothing on output 2 and output 7 is still
skipped over. Hmm...I replaced the transistor (bad one) for output 2
and that problem was fixed. Tried different chips: seven different
Fairchild CD4017BCN all had the skipping output 7 problem. Out of ten
Motorola MC14017BCP five worked perfectly. Problem solved, now all 8
outputs work properly.
Out of 17 chips I only have five good ones? I found this hard to
believe, so I re-installed one of the bunk Fairchild chips and
started swapping out different LM358s. I tried Fairchild and National
brands, and also LM2904. No change. Then I tried a TL072. Fixed it!
Then I tried TL082, BA4558,MC33077. All worked. It seemed any split
supply opamp worked. With the LM358 replaced by a TL082, I started
swapping out 4017s. Every one of the seventeen 4017s I have worked
perfectly!
Can anyone explain this ? I'm just starting to dig into CMOS stuff
and this really threw me. A nice thing about this discovery is maybe
I can finally get my Gated Comparator working properly since it
exhibits the same kind of skipping behavior.