Hello,
Please forgive me for saying this, but measuring the "resistance" of a
zener diode does not make a lot of sense. This component was designed to
break down in a controlled way when reverse-biased, at a predictable voltage level.
What you should be measuring is the voltage drop across the zener when it is in
the circuit and powered up. That's really the only thing you care about. It should
be close to its rated 3.9VDC. The exact voltage could be 3.7-4.1, depending on
the current. Zeners are not used when the voltage needs to be precisely set. In
that case some sort of laser-trimmed voltage reference would be used instead.
But you can tell if the diode is good (and if you have installed a 3.9V zener and not
a 1N4148. A normal switching diode (1N4148) will not break down with only 5V reverse-bias,
so you would see the full 5V of the power supply across it (the current will be essentially
zero, so the 120 ohm resistor will not have any voltage across it)
BTW, some time ago I uploaded some 'scope waveforms to the files section which you
could look at and compare to what you see on your board. Mostly they are related to
the CPU and the DAC scanning the pots, as that function is often affected by pcb corrosion.
But you may find them helpful.
Bob
--------------------------------------------
On Sat, 2/13/16, jw_dewdney@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:
Subject: [PolySix] PROGRESS!!!!
To: PolySix@yahoogroups.com
Date: Saturday, February 13, 2016, 12:55 AM
WOW. I can hardly believe it - everyone (who I am
incidentally VERY thankful to for their patience) will be
greatly relieved to know that I think i've LICKED my
problem.
How? On a weird
HUNCH - and thanks to Roman and Bob's suggestion - I
noticed that my D2 (the zener diode in question) was
measuring with a MUCH higher passive resistance than the
stock D2 zener on my original board (around 12 Megohm -
compared to close to 10K on the original for the same
polarity) - so after reading about shunting etc and how
zeners typically need a high value resistor (like the 10K
next to it) to help them function better in such circuits -
that something was off. I was wondering how the HECK the
zener i was using would work - assuming (perhaps wrongly)
that the current would rather flow through the resistor.
Okay- sorry - i'm being
too verbose. But anyway- I swapped in the OLD D2 from my old
polysix board - and NOW it sort of works - it's not
perfect... I still have program patch 4 and 5 eternally
lit... but other buttons and functions now seem to work. I
haven't tried to see if I have audio yet.... but this is
a HUGE leap forward to me... so again - thanks SO MUCH you
guys for helping... !
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