[Elecraft] How to check a diode? THANKS!!!!!

Fri Feb 28 16:08:01 2003

Ron -
Between you and Ed Tanton I got EVERYTHING I need to check out a problem tonite. You guys are just really super and it is so great to be able to get this kind of help - especially when I'm not an electrical tech - just a cw paddle jockey! Thanks very, very much.
Regards, Tim
> 
> From: "Ron D'Eau Claire" <[email protected]>
> Date: 2003/02/28 Fri PM 03:04:17 EST
> To: <[email protected]>
> Subject: RE: [Elecraft] How to check a diode?
> 
> First be sure it is a "multimeter" designed for solid state gear. Older
> "multimeters" use a voltage source for resistance checks that often far
> exceeds the allowable limits on solid state devices, including some
> diodes. 
> 
> I had an old "VOM" that had a 22.5 volt battery for resistance
> measurements! Fine for vacuum tubes, but a disaster around anything more
> sensitive than a power rectifier diode! 
> 
> As for checking a diode "in circuit" you can learn a lot by taking
> resistance and voltage measurements. First, recall that a diode conducts
> current in the "forward" direction  - positive lead to the anode (end
> with the arrowhead on the schematic) - and will not conduct current in
> the "reverse" direction. 
> 
> Of course, resistance is done with the power off.  If the resistance is
> much lower in the "forward" direction than it shows when you reverse the
> leads, the diode is probably good. I say "probably" because there might
> be ANOTHER diode somewhere in the circuit that is showing up, provided
> the diode being checked is open, not shorted. 
> 
> Reverse the leads and see if the resistance is much, much higher,
> indicating that the diode is "reverse biased" now and not conducting.
> It's very likely good if you see those readings. If the resistance is
> the same in either direction, it may well be shorted out. In that case
> I'd lift one end and test it "isolated". 
> 
> If the circuit has a d-c current flowing through the diode, you can
> check it with the power on by measuring the voltage to ground on both
> sides of the diode. Silicon diodes show, typically, a 0.6 volt drop
> across them. So the voltage on the anode side should be 0.6 volts higher
> than the other side. If the diode has a d-c reverse bias on it, the
> cathode end will show a positive voltage that is higher  - should be
> much higher - than the cathode side. 
> 
> In either case, it is very likely good if you get those readings.
> 
> Of course there are no "moronic" questions...
> 
> Ron AC7AC
> K2 # 1289
> 
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of [email protected]
> 
> If your only equipment is a multimeter, what is the proper way to check
> if a diode is good as an isolated component? What is the proper way to
> check if its shorted out when installed? I know, moron questions. Thanks
> guys. 73/Tim NZ7C
> 
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