reliably testing diodes in circuit ?

Certainly. Your meter can't tell the electrons to *only* to through the diode. They will go through whatever else is in the vicinity.

A diode by itself is not .567 one way and 0 the other. It is .567 (or so) one way and infinity ("overload") the other way, indicating that there is no path for the electrons.

In this case the electrons are finding a path through other components.

Why would you expect 0V ? That would indicate a short !

0.567V is about the right forward voltage for a diode check.

That's the non-conducting direction for the diode. The 1.897 V will come from other components in parallel with it. It's hardly unexpected !

I think you need to practice measuring some diodes before drawing incorrect conclusions as at present.

Graham

Yes.

Best regards, Spehro Pefhany

--
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LOL !

That's an unusually terse response from you there Spehro.

Graham

"robb"

** You meant the meter shows over-range, not " 0.000 " - OK ? ** As it will with a resistor of about 10 - 20 kohms ** It is generally not possible to make "reliable " tests on diodes that are still in circuit - certainly not with a DMM set to " diode test".

I find an old fashioned analogue multimeter to be far more useful ( since its has a test current of circa 50mA), but even it will not reliably find leaky diodes in circuit.

...... Phil

DMM

V) in

i

through the

.567 (or so)

that there is no

components.

Thanks for help and explanation.

regards, robb

DMM

V) in

apology, i mistyped. i meant to type 0L, at least that is what the meter displays when i use diode test on the DMM

Thanks for help.

(1.897 V) the other .

thanks Spehro.

DMM

V) in

OK ?

apology, yes, 0L on DMM display not 0V .

diodes that are

test".

useful ( since

reliably find

thanks for helpful explanation Phil.

I ran into a situation like that when trying to figure out what a little four-leaded device was. Turns out it's a diode ring - four diodes connected anode-to-cathode - intended for use in a balance mixer/modulator. For any two adjacent leads, it would read about .5 volts with the leads in one orientation and three times that voltage in the other direction... I was actually reading the forward voltage drop of either one or three diodes.

In your case, I expect that you're probably reading the forward voltage drop of the diode in one direction, and reading the effect of other components (diodes with the opposite orientation, shunt resistors, etc.) in the other. Since you're reading in-circuit, you cannot be certain that either reading is due solely to the diode you think you're measuring, and the actual number displayed is going to depend somewhat on the measurement technique used by the meter.

--
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Hi, Robb. When on diode check, the DMM typically puts out a current of a couple of mA, and then measures the voltage across the probes.

As mentioned elsewhere, doing a diode check on a diode in-circuit also measures everything else in parallel with the diode. The readings may have little or no meaning.

One exception -- if you're measuring a diode's forward voltage drop in- circuit, the reading has to be less than or equal to the diode drop out of circuit. If the reading is greater, that reliably indicates a problem with the diode. Since diodes do sometimes fail open, that data point can be of some use.

Cheers Chris