[sdiy] Vanilla electronics question

[mskala at northcoastsynthesis.com]

On Tue, 20 Feb 2024, Chris McDowell via Synth-diy wrote:

> Is it possible D1 is actually facing the other direction? Then it would just be reverse polarity protection, and the circuit is dead simple.

Similarly, is it possible it was *meant* to be facing in the other
direction, even if it isn't installed that way now?

Something I haven't been clear on throughout this thread is whether the
circuit in its present configuration was ever known to actually work in
the first place.  If it may possibly have been misrepaired in the past, or
incorrectly manufactured right from the start, then that could explain
both the unusual apparent circuit and why it isn't working and needs to be
fixed now.  And if it never worked in this configuration then "How is it
able to work in this configuration?" is less of a mystery.

It seems implausible that a commercial product would be designed to depend
for its operation on the reverse leakage of a Schottky diode far below
breakdown voltage.  But the described circuit can't function any other way
than that.  Even if it's meant to be some kind of oscillator, reverse
leakage would be necessary to start it and then unusual negative
resistance behaviour of the diode would be necessary to keep it running.

And even if someone can connect those components that way and get a
halfway useful result, it wouldn't be reproducible and appropriate for
mass production because it'd be depending on unspecified behaviour of the
components.  So it really seems most plausible to me that either the
circuit is not really as described, or that the circuit may be as
described now, but it was originally designed to be something else and
then either modified or incorrectly manufactured.

The Schottky diode might be installed backwards.  That might not have been
intended to be a Schottky diode - having a Zener instead might *sort of*
make sense.  The apparent resistor might actually be, or might have been
intended to be, a visually-similar inductor (wouldn't solve all the
problems but might be part of an oscillator circuit).  The power
connection might have been intended to go in the opposite direction, and
the connections of the LEDs misinterpreted.  And so on.

-- 
Matthew Skala
North Coast Synthesis Ltd.