Schottky diode Question. - test-drb@ccmp.vtda.org

2 Nov 1999

Well . . . MY DMM doesn't read the DIODE the same in both directions.  If it
reads the same when the DMM is in DIODE TEST mode (the only one which is
really meaningful) it should read the voltage across the diode.  If it's the
same in both directions, AND NO OTHER CONNECTED Devices are present, it's
not a diode.  In your case that probably means that it's broken.

If you're measuring it in situ, the other components in the circuit are
probably playing a role.

I don't have the data book on that diode here, so I'm guessing it's a
rectifier, and therefore has a forward voltage on the order 0.275 volts.
(SCHOTTKY diodes are preferable for rectifiers in portable devices because
they (1) require less voltage overhead, and (2) don't generate as much heat.

Be sure you know what you're measuring!

I've never had a battery on my notebooks go bad, so I don't know how they
behave when they do that, but I've seen some sensor circuits used in turning
the system on which don't work when the battery is in "deep discharge" as
it
might be if it was left on and became "empty" enough that the charge circuit
sees it as a short and defends itself by shutting down.

Try an external charger for the battery.  If that doesn't charge the
battery, then charge up a 7500 microfarad capacitor to about 75 volts and
discharge it through the battery, observing correct polarity.  That may blow
out any cilia which may be causing a cell to behave as though it's
collapsed.

good luck!

Dick

-----Original Message-----
From: jpero(a)cgocable.net &lt;jpero(a)cgocable.net&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Tuesday, November 02, 1999 4:28 PM
Subject: Schottky diode Question.

...
  It might work better if you use an unused gate or some
such.  Phantom often
...
  has numerous loads on it, so you could consider a pair
of OC gates if
 they're available.  Otherwise, a SCHOTTKY diode should suffice, since its
 forward voltage isn't enough to confuse any other device into missing the
 LOW on the PHANTOM line. 
I have measured  resistance both ways, it becomes less of a diode as
I go higher in resistance scale on my DMM, around 20K and up I read
like a piece of 100 ohm resistor both ways but reads fine on diode
mode.

BTW:  these are 1N5822.  I'm working on a bondwell 486NC2 notebook
seems to have power problem.  Even with batteries unplugged, charge
LED lights up same time as power lights up when I plug power brick
in.  Sometimes I can get hint of action and just once got computer to
boot up for few seconds then dies.

What gives?

Wizard