How did I blow out a leg of a Bridge Rectifier(BR82D)

[V8meathead]

So I'm building your basic DC power supply using Bridge Rectifier(BR82D) 200v 2A.  When I go to test the thing with my function generator, 18v P-P at 60Hz and look at it with my scope I get half wave rectification. 

PROCEDURE - After I first assembled the thing, I checked the output voltage of the regulator with my scope which looked to be OK.  Then proceded to look at the rectification with my scope on the legs of the BR82D, to find that it's only rectifying a half wave.  I can only conclude that I blew a leg out on the thing somehow when connecting the clips.  But I haven't any clue how I could have done so.  Im guessing that it may have to do with grounding, but I am not positive.  Anyone have any ideas?  Comments?  Maybe it had to do with which clips (+ or -) I connected first from the scope.

 

[Ldanielrosa1]

Your scope leads may be causing the problem.  If the either output form the bridge rectifier is electrically grounded then the scope ground lead may be providing a current path that you hadn't planned on.

 

[V8meathead]

thanks for the help Ldanielrosa.  I found out what was happening.  My function generator could only supply enough current to turn on 2 of the diodes resulting in the other two not rectifying.  I tested it on a transformer and it worked just fine.  Just something I never thought about. 

 

[Alun]

No as Ldanielrosa says, the problem is more likely to do with the fact that the function generator and ocillosope both sare a common ground. The 0V side of the output from the function generator is connected to the metal case which is earth bonded and so is the scope's case which forms is also the 0V side of the input. The problem doesn't exist with the transformer because its output is isolated from the earth and not bonded to it.

 

[V8meathead]

thanks Ldanielrosa and Alun.

actually wait a second.  I actually didn't use a regular transormer.  I used one of those 3 prong, variable voltage transformer things that can supply more current and has higher voltage ratings than a regular function generator.(smaller boxy thing and heavy as hell) I pluged it into the wall and threw together the leads off of that.  I thought that current was the case.  But your probably right considering my explaination does sound a bit weird.  Do they share the same ground then too? the scope and big transformer thingy?  I seriously don't know.  If you wouldn't mind explaining to me a little more I'd really like to understand it.  Sry for wastin your time lol

 

[V8meathead]

http://www.stacoenergy.com/variable_transformers.htm one of these things.  The plug and cord model.

 

[Alun]

So you mean a variac!

A variac is an autotransformer and the neutral connection is the same as the 0V which is also earthbonded at the consumer unit where the power enters your home. Normally at low output voltages this is safe but if something goes wrong and there's a break in the winding the output could become directly connected to the phase thus cooking anything attached to it and this could be you. There is also a high risk of short circuit when you connect it to other grounded instruments like signal generators and oscilloscopes and earth loops can form if the neutral is connected to earth. I recommend using an isolation transformer for maximum safety when using variacs.

 

[V8meathead]

Perfect.  Thanks!