Why is a transistor testing as a thyristor ? - UK Vintage Radio Repair and Restoration Discussion Forum

Jolly 7 · 27th Sep 2022, 7:44 pm

Amongst a batch of 2N2219A transistors I ordered recently, one is testing as a thyristor on my component tester. I repeated the test and got the same results. The others are correctly showing as NPN transistors. Could this be a manufacturing defect ?

duncanlowe · 27th Sep 2022, 7:48 pm

I guess it depends where you sourced them from. There's a lot of fakery around where unscrupulous sellers relabel things in the same package as something desirable, that is similar enough to avoid immediate detection. Maybe a thyristor in the same package got relabelled like the others as something it isn't?

Jolly 7 · 27th Sep 2022, 8:28 pm

These were sourced from an eBay seller in China. Also, on closer inspection, only the thyristor has 'Korea' embossed on the side. The remaining transistors also have a wide range of gains.

vidjoman · 27th Sep 2022, 9:15 pm

I’ve just repaired an amplifier with germanium output transistors in the output stage that read as JFET’s. This is caused by the high leakage between electrodes. Multipurpose testers often give misleading results when leakage is present. If you don’t get a result that is recognised then the device is faulty.

TonyDuell · 28th Sep 2022, 4:49 am

I had the reverse, some thyristors (bought from a usually reputable company) that turned out to be PNP transistors.

Caused a lot of confusion as due to the resistor values, the 'pull down' on the gate was enough to turn on the PNP transistor for all the emitter was -ve and collector +ve. So I was wondering why the 'thyristor' was always on...

Jolly 7 · 28th Sep 2022, 8:17 pm

Thanks for all the replies. I guess I won't use this particular transistor for anything too critical and maybe just keep it for breadboard projects.

orbanp1 · 3rd Oct 2022, 1:05 pm

Hi Jolly,

Go back to the basics, do test the transistor in the "conventional way".
Test for C-E short, for C-B and E-B diodes, for Hfe on a multimeter.
You could also check for Ice0.
There are links in the "Sticky Thread" section on how to test a transistor.
Compare your test results with a transistor that test OK on your tester.

I am guessing you have one of those eBay component testers.
As that tester tests so many type of components, it sometimes has trouble identifying the component when the measured parameters do not fall into the expected range.
It does not necessarily mean that your transistor is faulty.

Here is an engineering document on such a tester, it has a section in it that describes how the tester tries to measure and identify a component.
That might give you some clue to the test results that you see.
https://raw.githubusercontent.com/lo...sh/ttester.pdf
(There might be a newer version of that document.)

Here is the original web-site of the tester project:
https://www.mikrocontroller.net/arti...ansistortester

Regards, Peter

Jolly 7 · 5th Oct 2022, 4:46 pm

Thanks Peter. I will follow your suggestions and provided links.

27th Sep 2022, 7:44 pm	#1
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Why is a transistor testing as a thyristor ? Amongst a batch of 2N2219A transistors I ordered recently, one is testing as a thyristor on my component tester. I repeated the test and got the same results. The others are correctly showing as NPN transistors. Could this be a manufacturing defect ?

27th Sep 2022, 7:48 pm	#2
duncanlowe Nonode Join Date: Jan 2016 Location: Stafford, Staffs. UK. Posts: 2,532	Re: Why is a transistor testing as a thyristor ? I guess it depends where you sourced them from. There's a lot of fakery around where unscrupulous sellers relabel things in the same package as something desirable, that is similar enough to avoid immediate detection. Maybe a thyristor in the same package got relabelled like the others as something it isn't?

27th Sep 2022, 8:28 pm	#3
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Re: Why is a transistor testing as a thyristor ? These were sourced from an eBay seller in China. Also, on closer inspection, only the thyristor has 'Korea' embossed on the side. The remaining transistors also have a wide range of gains.

27th Sep 2022, 9:15 pm	#4
vidjoman Dekatron Join Date: Jun 2013 Location: East Sussex, UK. Posts: 3,326	Re: Why is a transistor testing as a thyristor ? I’ve just repaired an amplifier with germanium output transistors in the output stage that read as JFET’s. This is caused by the high leakage between electrodes. Multipurpose testers often give misleading results when leakage is present. If you don’t get a result that is recognised then the device is faulty.

28th Sep 2022, 4:49 am	#5
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Why is a transistor testing as a thyristor ? I had the reverse, some thyristors (bought from a usually reputable company) that turned out to be PNP transistors. Caused a lot of confusion as due to the resistor values, the 'pull down' on the gate was enough to turn on the PNP transistor for all the emitter was -ve and collector +ve. So I was wondering why the 'thyristor' was always on...

28th Sep 2022, 8:17 pm	#6
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Re: Why is a transistor testing as a thyristor ? Thanks for all the replies. I guess I won't use this particular transistor for anything too critical and maybe just keep it for breadboard projects.

3rd Oct 2022, 1:05 pm	#7
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Why is a transistor testing as a thyristor ? Hi Jolly, Go back to the basics, do test the transistor in the "conventional way". Test for C-E short, for C-B and E-B diodes, for Hfe on a multimeter. You could also check for Ice0. There are links in the "Sticky Thread" section on how to test a transistor. Compare your test results with a transistor that test OK on your tester. I am guessing you have one of those eBay component testers. As that tester tests so many type of components, it sometimes has trouble identifying the component when the measured parameters do not fall into the expected range. It does not necessarily mean that your transistor is faulty. Here is an engineering document on such a tester, it has a section in it that describes how the tester tries to measure and identify a component. That might give you some clue to the test results that you see. https://raw.githubusercontent.com/lo...sh/ttester.pdf (There might be a newer version of that document.) Here is the original web-site of the tester project: https://www.mikrocontroller.net/arti...ansistortester Regards, Peter

5th Oct 2022, 4:46 pm	#8
Jolly 7 Octode Join Date: Feb 2018 Location: Southampton, Hampshire, UK. Posts: 1,061	Re: Why is a transistor testing as a thyristor ? Thanks Peter. I will follow your suggestions and provided links.