Fabio421

Uhhhh? In english? How do you diagnose a short in a circuit board?

BTW, I did install it correctly.

Angel84-928

1. Lift one lead of the component from the circuit board.

2. Get a multimeter and set to read amps.

3. Connect one meter lead to the lifted diode lead.

4. Connect the other meter lead to the circuit board where you lifted the component lead. (This completes the circuit and places the meter in series)

5. Power the unit up an you'll read the current running thru that part of the circuit.

docmirror

If you're smoking diodes you've run too much current through them in the bias direction(forward bias). Unless you exceed the PIV(reverse bias) voltage for a fairly long time, you won't do any harm to the diode. You'll need to find out why so much current is being drawn in the circuit. This can get a bit daunting.

If you have an ammeter scale on your DMM, you can connect the ammeter in place of the diode, and find out what the current draw is. I would start on the 10 amp scale and see what you get. Also, note the polarity of the current flow.

Take the diode out, get a new one 1N4007 and solder one end in. Solder a small stub wire in the other hole. Connect the leads of the ammeter to the stub and the lead sticking up from the diode, and try it again. See what current you get. You need all of the current flowing through the diode and the meter.

Angel84-928

^-----^
What I said but better.

Fabio421

Wow! Thanks guys. I'll try that and get back to ya'.

Alan

In this application these diodes should have no DC current flowing. They are between a switched output and ground - reverse biased for spike protection only.

The only way they can sink DC current is if they are installed reversed or if their junctions are destroyed and start actiing like low value resistors.

If you installed it correctly and did not disturb the rest of the circuit in any way then you have surely blown it up. Its certainly possible that the PIV was exceeded by a switching spike and this fatally damaged it. Doc contrary to what you said - junction damage occurs very rapidly - it is likely there is good margin to the PIV voltage spec - but once the actual limit is exceeded the junction will be destroyed almost immediately.

I'd suggest you get a higher PIV diode - current capacity should not be an issue.

Alan

docmirror

Which is why I advised in my post to change to a 7 from a 3........

And the PIV breakdown can be rapid, or it can take it for a long time, depending on the substrate junction design. If it's a cone junction, which is very common in cheap diodes it'll take a lot of PIV for a long time, if it's planar, or sandwich, it'll blow quickly. YMMV.

Ed Scherer

I don't know if it's been mentioned yet, but when soldering in semiconductor devices like diodes, I'd recommend using a little clamp-on heat sink close to the component (between the component and where you're soldering the lead) to wick away heat while you're soldering. And don't heat any longer than you need to.

Don't want to kill the component before it ever even has a chance to power up.