How do I identify the value of a diode for a polarity check of a 19 Volt DC circuit?

Question

I mean to replace it if it shows it is open in both directions.

Answer 1

If you are asking how to test the diode grab a Digital Multimeter DMM with a diode test built in. They are inexpensive (under $20 US) and there are many uses for them. Make sure it has a diode test setting.

With no power applied to the circuit and my batteries disconnected touch the leads of the DMM across the diode and watch the display. Now reverse the leads and repeat. You should get a high reading one way and low the other. If so the diode passes. If you get a low both ways the diode is shorted and ( or in parallel with low resistance circuitry don't worry we will test for that.) If it reads high both ways it is probably open. If the diode failed desolder one end of the diode. Repeat the test. if it passes it is good. If it fails now replace it.

Did that answer what you wanted?

Answer 2

do you mean what value will your ohmmeter read?

not relevant, and depends on the design of your ohmmeter. But it will be in the ohm range forward and the Megohm range reverse.

edit: to replace it , you need the part number which may be printed on the diode. If not, you have to look at the circuit and figure out the specs from that.

If this is a 19 volt supply, and the current is 1 amp or less, at 50 or 60Hz, then something like a 1N4002 would work.