Is there a way to test diodes?

[Wales]

I've gone on geo and read how to test diodes but i don't have that function on my DMM and don't have an analogue meter. Is there a way I can test the difference between diodes with a standard DMM?

The reason I ask is that i built a Violet Ram's Big Muff and put a switch to swap from si diodes to LED'S. For one set of diodes I put little yellow LED'S and for the other set little green LED's. If i put the LED's on instead of the diodes I blow Capacitor 13  after a while. I have replaced this capacitor twice now and its gone again.
  1. Can I bump up or down the value of C13 to fix this?
  2. If I change C13 will it mean i need to change other parts in the circut?
  3. Would standard red LED's work better (goin to get more today)?

Here is my original thread with all the modifications and the schematic and parts layout for the build. And voltage reading from my original problems.

http://www.diystompboxes.com/smfforum/index.php?topic=75222.msg612404#msg612404

[doitle]

You said you dont have an analog multimeter? Do you have a digital one? That's what I use to test diodes. Just set it to something like 2K Ohm mode or 20K mode. A fairly low resistance but above a thousand. Then touch one probe to a lead on the diode and the other probe to the other lead. If it reads Infinity or 1 as mine does when it is above the range, flip the diode around. It should read a small resistance now. That's all that's needed I think. If it behaves like that you've got a working diode. Just tried it out while explaining it on this .... SD333? Diode I had sitting here. Big diode looks like it was from a power supply or something. In one direction it reads 1 or infiinte resistance and the other way it reads 135 ohms. Thus it is a working diode.

>_< I sure hope this is good information and I'm not wrong and spreading wrongness...

[Mike Burgundy]

It might be a good idea to invest in a slightly "bigger" DMM - at least with diode test, continuity beep and perhaps a transistor HFE tester (although these are inherently flawd - leakage shows up as extra HFE).
That said, it might be so that your meter measures resistance at voltage levels (it needs to put voltage across whatever you're measuring to determine the resistance, no way around it) that are *too low* to turn on a semiconductor. Diodes (semiconductor!) have a threshold voltage below which they won't conduct. My meter measures resistance at such a low voltage that they don't turn on, which can be handy measuring things in-circuit.
If you don't have any possibility to test diodes with a meter, why not use a battery, resistor (1k or something, whatever lights the LED nice and bright without frying it), LED and some alligator clip leads - use the battery, resistor and LED in a normal setup as you would in a pedal and verify the LED lights. Now clip the diode under test *between* the LED and battery (or anywhere in the chain as long as it's in series). The LED should light with the diode in it's conducting direction, and not the other way round.

[Wales]

Yeah my meter has a hFE function and of course continuity but no diode test.  I got some readings off of the LED'S but i had to use the hold button cause it would flash its value and then light the LED.
LED's  Green 1.939K
         Yellow 1.895K
         Red (not used) 1.776K
Diodes 1N914  0.904K

Because the diodes I am using are 1K different voltage drop would this lead to the breakdown of C13? If so how could I stop this and keep the LED's the same? or am I missing another problem?

Thanks for any help

[sean k]

On my one the diode test is the continuity test, maybe you've already got it. One way it measures the voltage drop and the other it doesn't do anything. Try them using continuity.

[Mike Burgundy]

Strange - I see no reason why C13 would blow under normal conditions - what's it rated to? The value isn't exactly important (well, to the sound it is, not as far as staying in one piece though) but it's voltage rating is. I'd say there is another problem, though. Check wiring, take ckt voltages, post, take it from there?