Testing a ZNR and other

[Uriah]

Thanks to everyone for all of the help that I have received through
this group. This one and the Pinball newsgroup are the most helpful
newsgroups there are.

I have a few components that I am having trouble finding out how to
test. One is a zinc oxide nonlinear resistor. It is labeled on the
board as ZNR1 the symbol is a Z on its side. It is has two legs and
is orange, kind of shaped like a capacitor. On it is written 10N471K
under that is 66+. It is some kind of protection device. If I test
it on a Huntron it shows a capacitor like signature. It is not
shorted. How do I know that this thing is OK. How would I test to
know that it is OK. Everything I read requires equipment I don't
have. Does this operate on AC or DC in the circuit. Is it to protect
for over voltage or reversed voltage? How is it supposed to work? Is
it a one time thing that goes short or open when it is in action or is
it something that works by keeping a voltage in check?

The other thing is a blue square two legged device. The symbol on the
board where it is mounted shows a capacitor and a resistor and is
labeled R63 which implies that it is a resistor of some sorts. But why
is there a capacitor symbol along with the resistor symbol on the
schematic and the board. Written on it is 100nM +120K, Under that is
PCRC 420 250V~2, and under that is PILKOR WK0626. What am I testing
this thing for? Resistance and capacitance? How do I know when it is
failing or has failed? All of these new components always leave me
guessing.

Thanks very much
Russ

 

[Ross Herbert]

:Thanks to everyone for all of the help that I have received through
:this group. This one and the Pinball newsgroup are the most helpful
:newsgroups there are.
:
:I have a few components that I am having trouble finding out how to
:test. One is a zinc oxide nonlinear resistor. It is labeled on the
:board as ZNR1 the symbol is a Z on its side. It is has two legs and
:is orange, kind of shaped like a capacitor. On it is written 10N471K
:under that is 66+. It is some kind of protection device. If I test
:it on a Huntron it shows a capacitor like signature. It is not
:shorted. How do I know that this thing is OK. How would I test to
:know that it is OK. Everything I read requires equipment I don't
:have. Does this operate on AC or DC in the circuit. Is it to protect
:for over voltage or reversed voltage? How is it supposed to work? Is
:it a one time thing that goes short or open when it is in action or is
:it something that works by keeping a voltage in check?
:
:The other thing is a blue square two legged device. The symbol on the
:board where it is mounted shows a capacitor and a resistor and is
:labeled R63 which implies that it is a resistor of some sorts. But why
:is there a capacitor symbol along with the resistor symbol on the
:schematic and the board. Written on it is 100nM +120K, Under that is
CRC 420 250V~2, and under that is PILKOR WK0626. What am I testing
:this thing for? Resistance and capacitance? How do I know when it is
:failing or has failed? All of these new components always leave me
:guessing.
:
:Thanks very much
:Russ


It is a 470V varistor. You'll find it mentioned in the Fairchild app note.
http://www.fairchildsemi.com/an/AB/AB-46.pdf

 

[Paul E. Schoen]

Thanks to everyone for all of the help that I have received through
this group. This one and the Pinball newsgroup are the most helpful
newsgroups there are.

I have a few components that I am having trouble finding out how to
test. One is a zinc oxide nonlinear resistor. It is labeled on the
board as ZNR1 the symbol is a Z on its side. It is has two legs and
is orange, kind of shaped like a capacitor. On it is written 10N471K
under that is 66+. It is some kind of protection device. If I test
it on a Huntron it shows a capacitor like signature. It is not
shorted. How do I know that this thing is OK. How would I test to
know that it is OK. Everything I read requires equipment I don't
have. Does this operate on AC or DC in the circuit. Is it to protect
for over voltage or reversed voltage? How is it supposed to work? Is
it a one time thing that goes short or open when it is in action or is
it something that works by keeping a voltage in check?

The other thing is a blue square two legged device. The symbol on the
board where it is mounted shows a capacitor and a resistor and is
labeled R63 which implies that it is a resistor of some sorts. But why
is there a capacitor symbol along with the resistor symbol on the
schematic and the board. Written on it is 100nM +120K, Under that is
PCRC 420 250V~2, and under that is PILKOR WK0626. What am I testing
this thing for? Resistance and capacitance? How do I know when it is
failing or has failed? All of these new components always leave me
guessing.

An MOV (ZNR1) can be tested by applying a variable DC voltage through a
limiting resistor of about 100k. You can read the leakage current with a
DVM across the resistor. When you see the current start to rise quickly
with increased applied voltage, that will be close to the rated breakdown
voltage of the device, which is in this case is about 470V although the
actual breakdown may be about 600VDC.

R63 is a snubber which has a 100nF capacitor and probably a 120 ohm (not
120k) resistor in series with it. You can test it with an RCL meter that
gives ESR, or apply an AC current and observe the phase shift with a scope.
At low frequencies it will act as a capacitor, and at high frequencies it
will act as a resistor, so you can test it that way as well.

Paul

 

[Russ]

Thanks for the help. Could you clarify a few things?

which is in this case is about 470V although the

actual breakdown may be about 600VDC.

Do I need to get a 400-600 volt DC source to do do this test? Lets
say I have this device. Would I need a meter to handle this voltage
also right? Then I would put a DVM in line with it to monitor the
current. Should it not allow any current to flow at lower voltage and
then when it gets to 600VDC I would see a rush of current flow at its
breakdown point. Does that then fry the device? All of this makes
sense. Could I use a Megger type tester to do this?

You can test it with an RCL meter that
gives ESR,

With the Snubber, I have a RCL meter, one of those smart tweezers.
Would that 120 ohm resistor always show up when reading ESR? Would
that interfere with the low ohm leakage that ESR usually reports? If
it was only a cap, and I got something like 4 ohms with an ESR meter,
would this device then add the 120 ohms to that? I am not sure I
would know what is a correct reading would be when using a scope to
watch the phase. I don't have a known working one of these to compare
with. Same with the ZNR. I would have to order a few of them to be
able to compare a known working one to the ones I have.

Thanks for the help
Russ

 

[whit3rd]

I have a few components that I am having trouble finding out how to
test.  One is a  zinc oxide nonlinear resistor.  It is labeled on the
board as ZNR1 the symbol is a Z on its side.   It is has two legs and
is orange, kind of shaped like a capacitor.  On it is written 10N471K
under that is 66+.  It is some kind of protection device.  If I test
it on a Huntron it shows a capacitor like signature.  It is not
shorted.  How do I know that this thing is OK.  

Don't bother. In normal operation, this kind of protection device
passes
little or no current, and you've already verified that behavior.
Like a fuse, it does very exciting things when a power surge comes in,
but
if you DO apply such a surge, it (like a fuse) might change behavior.

Low-power testing is possible, but that takes (at minimum) a HV
transformer and appropriate safety precautions, and your test
will only cover a small subset of the specification sheet behaviors.

 

[Paul E. Schoen]

Thanks for the help. Could you clarify a few things?


Do I need to get a 400-600 volt DC source to do do this test? Lets
say I have this device. Would I need a meter to handle this voltage
also right? Then I would put a DVM in line with it to monitor the
current. Should it not allow any current to flow at lower voltage and
then when it gets to 600VDC I would see a rush of current flow at its
breakdown point. Does that then fry the device? All of this makes
sense. Could I use a Megger type tester to do this?

Yes, a Megger should work. Or a hipot. As long as the current is limited,
the device should not be damaged or degraded. You should be able to apply
the rated working voltage plus a bit more and see a high resistance and no
breakdown. These devices usually fail shorted or leaky at lower voltages,
so you should be able to detect a bad one. It will usually test as a
capacitor.

With the Snubber, I have a RCL meter, one of those smart tweezers.
Would that 120 ohm resistor always show up when reading ESR? Would
that interfere with the low ohm leakage that ESR usually reports? If
it was only a cap, and I got something like 4 ohms with an ESR meter,
would this device then add the 120 ohms to that? I am not sure I
would know what is a correct reading would be when using a scope to
watch the phase. I don't have a known working one of these to compare
with. Same with the ZNR. I would have to order a few of them to be
able to compare a known working one to the ones I have.

It may depend on the specs of the LCR meter to see if it will discern a 120
ohms resistance in series with the capacitance. The ESR of the capacitor
should be in milliohms. You could use a known good capacitor and resistor
in series and compare the waveforms. The Huntron tracker would work well,
or a Lissajous pattern on a scope.

Thanks for the help
Russ

You're welcome,

Paul