schottky diode again..

From: jpero_at_cgocable.net <(jpero_at_cgocable.net)>
Date: Wed Nov 3 13:36:55 1999

> Date: Wed, 3 Nov 1999 23:35:23 +0000 (GMT)
> Reply-to: classiccmp_at_u.washington.edu
> From: ard_at_p850ug1.demon.co.uk (Tony Duell)
> To: "Discussion re-collecting of classic computers" <classiccmp_at_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
Received on Wed Nov 03 1999 - 13:36:55 GMT