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When I looked up how to measure varistors, I found that the varistor's value should be 0L ohms (Over range, infinite resistance) when measured by a DMM set to test resistance, to indicate its validity.

When I tested the varistor (INR 14D681S) with my DMM (Set on resistance test mode), the result was 0.650 MOhms (Knowing that both its legs are attached to the PCB).

It's at the gate of receiving the VAC to protect the entire circuit (I point at it with red arrow.) One of its legs is connected to the ground terminal & the AC terminal, when the relay is engaged via a parallel connection with a capacitor (470n K275V~ 436D MKP X2,) the blue box above it.

There's no sign of burning or explosion on it as I saw in demo videos when it receives higher voltage than its value.

Do I need to detach one of the varistor's legs as regular resistors to get a right reading?

Do I need to detach it & test it with DMM if there's no visible sign of damage on it?

enter image description here

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  • \$\begingroup\$ "When I looked it up I found that Varistor's value should be 0L Ohms." Please post a link to the datasheet. Please also explain why you think it needs investigation. \$\endgroup\$ – Transistor May 2 '20 at 11:49
  • \$\begingroup\$ @Transistor I edited the question and added the link to its datasheet. The reason that when I measured other varistors (blue ones), their values were 0L, so why it's different. Thank you in advance. \$\endgroup\$ – Ashraf Alshahawy May 2 '20 at 11:59
  • \$\begingroup\$ What does 0L mean to you? It means nothing (as in nothing springs to mind) to me. \$\endgroup\$ – Andy aka May 2 '20 at 12:03
  • \$\begingroup\$ (1) "When I looked it up I found that the varistor's value should be 0L ohms." The word 'ohm' doesn't appear to be in the document you linked. (2) You say 'when I looked it up' but your comment is discussing measurement. Which is it? '(3) OL' usually appears on a multimeter to indicate over-range on a measurement. For resistance it means that it is higher than the meter can measure - effectively an open-circuit. \$\endgroup\$ – Transistor May 2 '20 at 12:05
  • \$\begingroup\$ It means to me that its resistance is so high to be measured by my DMM which is limited by 40M Ohms. \$\endgroup\$ – Ashraf Alshahawy May 2 '20 at 12:06
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The varistor (INR 14D681S) reads 0.650 MOhms while it is attached to the PCB.

That seems about ball-park correct

enter image description here

The data says that the DC voltage that produces 1 mA current is 680 volts (as per the "681" in the part number. 680/1 mA = 0.68 Mohms.

Your meter read 0.65 Mohms so it's about right. If you pulled a leg out it might read a few Mohms BUT, the important thing here is that you haven't found a problem with the MOV with your test.

Do I need to detach it & test it with DMM if there's no visible sign of damage on it?

If it's failed then your multimeter test will not show this whether it's in-circuit or sat on your bench. At the moment, it looks OK but, importantly what are the symptoms that caused you to suspect this component?

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  • \$\begingroup\$ Thank you for such detailed answer, really appreciated and I learned a lot from it. As for the symptoms to suspect it, it's my despair to find the problem in the circuit that causes it not to function appropriately LOL. Plus when I found the others readings are 0L while this one is 0.650 and in this guidance it says "If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown." ourpastimes.com/test-varistor-7675090.html \$\endgroup\$ – Ashraf Alshahawy May 2 '20 at 12:29
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    \$\begingroup\$ If I went to the doctor and told him I am unable to function appropriately and offered no other words, do you think he could explain what was wrong with me LOL!!! \$\endgroup\$ – Andy aka May 2 '20 at 12:35
  • \$\begingroup\$ I didn't wanna take advantage of you and burden you with the details of the problem, which's simply that the PCB belongs to a Washing Machine that powers up normally but when I press the Start button, it makes a different sound than it used to be, and it doesn't start the program, as in this video youtube.com/watch?v=52NltT5C8Es. Which left me under a heavy load of dirty cloths LOL \$\endgroup\$ – Ashraf Alshahawy May 2 '20 at 12:50
  • \$\begingroup\$ Ah that's unfortunate (especially with covid 19). I don't think I'll be able to assist further given what the circuit board is from. Worth a shot though. \$\endgroup\$ – Andy aka May 2 '20 at 12:53

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