[sdiy] Issue with CD4024 Ripple Counter

David G Dixon dixon at mail.ubc.ca
Tue Sep 21 03:18:58 CEST 2021


Just for Ss and Gs, I thought I'd show you my layout graphic for the ASR
board which has the clock circuit on it.  Please see attached.  Note that
red traces are the +V rail and green traces are the GND rail (and black
traces are the -V rail).  The CLOCK pin of the 4024 is connected to the
light blue trace.  I've also attached what I call the "Build" picture, which
is what the board actually looks like.  Finally, I've attached a picture of
the actual board.  Note that there is another circuit board that this one
plugs into, which has a DG333 and comparators for controlling the
"Shift/Bypass" switches on each ASR channel electronically.  That's what the
3- and 4- pin headers plug into.  The 4-pin header passes through that board
and connects to the Panel PCB.  This is where the clock signal comes in and
out of this board.
 
The rail traces are a bit thicker than the other traces.  You will notice
that the ground traces do not connect to each other across the top of the
board, so that the ground at the 4024 actually comes up from the bottom.  I
just tried jumpering the two ground traces temporarily with alligator clips
and it had no effect (and why should it?).
 
Also, I should mention that when the ASR is being clocked by an external
LFO, the CD4024BE is clocking on the positive edge only.  However, when the
Manual clocking switch is used, the CD4024BE is clocking on both edges.  The
clock signal at the CLOCK pin looks identical in either case.  The manual
clocking switch is connected to the +V and GND rails, and is fed to the
comparator through a 1k resistor, whereas the clock input jack is connected
through a 10k resistor.  Why any of this should have an effect is beyond me.
This, for me, is now more or less in the realm of the supernatural, in terms
of my ability to understand it.
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