When I test an NTE5556 SCR with a multimeter set on diode test, I get 0.6 ohms
with either the positive or negative lead on the annode or cathode. On regular
resistence, I get 55 ohms. Shouldn't I only get a low reading in one direction
as if testing a diode? The device is not failed, new one checks the same.
When I use an in-circuit transistor tester I bought at JayCar, I get open
circuit. Doesn't seem to respond like a normal SCR.

(WbSearch) writes:

When I test an NTE5556 SCR with a multimeter set on diode test, I get 0.6 ohms
with either the positive or negative lead on the annode or cathode. On regular
resistence, I get 55 ohms. Shouldn't I only get a low reading in one direction
as if testing a diode? The device is not failed, new one checks the same.
When I use an in-circuit transistor tester I bought at JayCar, I get open
circuit. Doesn't seem to respond like a normal SCR.

An SCR should test open circuit with positive on the anode, negative on
the cathode, gate open or connected to cathode. Are you sure the pinout
is correct?

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Yes, I checked it 3 times. 2 new ones check the same, confused me but I
installed one and the device now works. The one I removed checked 0.2 ohms ILO
0.6. I also tried shorting the gate to annoded with the other lead on the
cathode to see if it would stay "latched". It did not, as soon as I removed
the gate, it went open again.

"WbSearch" bravely wrote to "All" (25 Mar 04 13:59:14)
--- on the heady topic of " Testing an SCR"

Only low power SCR's can be tested reliably with an ohmmeter. An
ohmmeter doesn't have enough current to drive a high power SCR properly.
High power SCR's must be tested on a jig of some type. It can be as
simple as a 100 watt lamp on a base with a 120 volt alternating supply.
It won't test the full current but is an easy to do go/no-go test.


Wb From: (WbSearch)

Wb Yes, I checked it 3 times. 2 new ones check the same, confused me but
Wb I installed one and the device now works. The one I removed checked
Wb 0.2 ohms ILO 0.6. I also tried shorting the gate to annoded with the
Wb other lead on the cathode to see if it would stay "latched". It did
Wb not, as soon as I removed the gate, it went open again.

Thanks. That explains it as this particular SCR is 400 volt, the usual ones I
test are around 100 volt.

(WbSearch) writes:

Thanks. That explains it as this particular SCR is 400 volt, the usual ones I
test are around 100 volt.

The type of SCRs you find in consumer electronics should be able toe
test with a multimeter. He's talking about high power high current
SCR hockey pucks.

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the feedback form on the S.E.R FAQ Web sites.

WbSearch says in da message in da
phuck'n group sci.electronics.repair:
When I test an NTE5556 SCR with a multimeter set on diode test, I get 0.6 ohms
with either the positive or negative lead on the annode or cathode. On regular
resistence, I get 55 ohms. Shouldn't I only get a low reading in one direction
as if testing a diode? The device is not failed, new one checks the same.
When I use an in-circuit transistor tester I bought at JayCar, I get open
circuit. Doesn't seem to respond like a normal SCR.

There is a section on SCR testing at the Semiconductor Testing FAQ (more like an
HOW-TO, IMHO) at www.repairfaq.org .


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I found the section on testing SCR's, thanks. The one I replaced was in a
TO220 case used in a photographic flash. I thought the diode test position on
my DMM would provide enough current to test this device. Obviously not.
Thanks again for the helpful replies.