Diode Testing

Diode Testing. Testing a diode is relatively straight forward with a simple ohmmeter.

Set your ohmmeter to the highest scale. Disconnect all voltage from the diode.

Place the meter leads one on each lead of the diode. It should show either open or very low resistance it doesn't matter which just now.

Reverse the meter leads and the reading should be the oposite of the first test if it is your diode is probably fine.

Be aware that high current or excess heat can cause diodes to fail under load and test fine in this manner, however.

If you have a low ohms reading both ways then your diode has a short [or is shorted].

If you have a high reading both ways your diode is open.

A Bridge Rectifier is simply a collection of diodes arranged in a specific manner and can be either made from individual diodes or contained in one package with 4 leads. 2 input leads and 2 output leads [one + and one -]

In a schematic it looks like this:

To test a Bridge rectifier you can test it pretty much like the diode. One lead on one input lead and one lead on one output lead should show the same results as a diode test. You simply do this for each input lead to each output lead.

The output leads will show opposite behavior on each input lead from same input lead. The AC [input] leads should show infinity or very high resistance either way between the leads. The DC [output] leads should test like a normal diode across these leads, high resistance or infinity and low resistance the other way.