Date: Wed, 3 Nov 1999 23:35:23 +0000 (GMT)
Reply-to: classiccmp(a)u.washington.edu
From: ard(a)p850ug1.demon.co.uk (Tony Duell)
To: "Discussion re-collecting of classic computers"
<classiccmp(a)u.washington.edu>
Subject: Re: schottky diode again..
One minor point is to know how your DMM actually
measures resistance and
does the diode test. Just in case it's doing something strange.
The diode test range is similar. It applies a suitable current (a few mA)
to the diode under test and displays the voltage drop across it. I
On mine, on diode mode, if my calculations is correct it sources well
under 1mA, more like .668 mA (note the period!) or 668 uA across 1K
for .668 V drop across it. I'm rusty with this unit conversion so be
patient with me. But good thing I remembered the ohm's law. (!)
The polarity thing, it is the case with my meter, has to switch
probes to complete both forward and revserese tests.
Neither of these tests should be confused by a Schottky diode, so I agree
that if you have one that appears to do the same thing both ways, it's
defective.
Appears to be when using resistance ranges. I better build the
modest current draw (say 500mA or so) light bulb and few cells and
see what happens.
A decent test device should source bit more current than 2mA more
like 200mA or more to simulate the "loading" on devices to
bring out the bad charactersics in most devices?
But you might want to test a couple of known-good
diodes with your meter
to be sure.
Done. And shows correct results but don't have brand new schottky
diodes around. Old hat, sigh.
I'm the sort of person who does odd things with new test gear to see how
it behaves. Like checking how the diode test range works (What does it do
if the diode is backwards, etc).
Didn't thought of being that sneaky to explore more in test devices
in *other ways around* with other tools testing the tool under test.
I have done that "cap charge/discharging tests" in past, DMM and
analog meter, (no longer have it, was cheapo Radio Shack unit),
reacted exactly the same like a analog and used it for some cases but
I prefer the ESR for true capacitors testing.
-tony
Wizard