Jump to content
Sign in to follow this  
Save Old Iron

How To - Test a Diode

Recommended Posts

Please note the position of the "band" on the diode and what color lead (positive / red or negative / black) is connected banded lead of the diode. Diodes are the equivalent of check valves in the world of plumbing or hydraulics. Current should only flow in one direction thru the diode. Current flow should be present when the negative / black lead of the multimeter is connected to the banded lead of the diode and the positive / red lead is connected to the opposite lead. 

 

(click on image to enlarge)

diodetesting_zpsfb82f8c3.gif


The diagram below shows a defective diode that has an internal short circuit in the body of the diode. The diode no longer has a "one way" characteristic and acts as if it were a piece of wire - current will flow in either direction thru the shorted diode so meter lead orientation makes shows no difference. In the world of plumbing or hydraulics, the check valve would be "stuck open".

diodetestingshorted_zpsca06286e.gif


The defective diode below is the equivalent of a burned out fuse. No current can flow thru the diode in either direction. The meter readings show a high resistance to current flow in either lead orientation. The hydraulic equivalent would be a check valve was "stuck closed".

diodetestingopen_zps50f158bd.gif

  • Like 1

Share this post


Link to post
Share on other sites

Just think of a diode as a one way check valve for the flow of electrons.

Share this post


Link to post
Share on other sites

Great post!  and to add...

 

...which is why LED's are polarized (only work when hooked in correct polarity). ( Light Emitting Diodes. :-)  )

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By diddy78c
      Last week I was hauling the c-121 back from my daughters softball practice (I used it to drag the diamond) and I made a right hand turn and stopped at the stop sign. As I made the left onto a non busy county road I watched in my right mirror as my horse decided it didn’t want to be trailered any longer. It rolled over 1 completely time and sat on its wheels. Unfortunately it broke some parts and tweaked the hood and deck lower-lift handle. I did manage to put it back on the trailer as a tripod and get it home. Always check your straps and rigging. Found the ratchet failed in my case. And unfortunately i cannot download a picture for this🤨

    • By S.J.
      Hello! I have a 1975 C-100 lawn tractor, and it's in pretty decent shape. Only problem is the mower deck is shot. I've been browsing for used decks, but I'm not seeing any of the original part number, s-0622. So I'm wondering, what other decks would be compatible with this model? 
       
      Thanks! 
    • By MS GENERAL REPAIR
      Part 1 of John Deere STX Lawn Tractor Repair Video Series.
      The Engine won't crank.
       
       
    • By stonecottage227
      Wanted - 1975 C100 Seat - I would also consider a cover as well
    • By Sarge
      Has anyone found a fuel gauge type cap to fit the 2-1/4" threaded neck on the plastic tanks in the C-series? My current cap leaks at much over 3/4 tank, would love to get a better-sealed unit with a gauge on it. I did find a Kelch to fit the D, it's a bit short but works great and doesn't leak, while still vented correctly.
       
      Sarge
×