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 Post subject: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 12:18 am 
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Joined: Nov Thu 22, 2007 11:31 pm
Posts: 1006
Location: Johnston, Iowa
All, I found on-line a description for an in-circuit transistor testerhttps://www.industrial-electronics.com/p-e_elec-exp-hb-1982_transistor.html . This was published in 1982 in the Popular Electronics Electronic Experimenter's Handbook. I built one but haven't tested it yet. Is anyone familiar with this circuit and will it be useful?
Thanks,
Keith


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 12:58 am 
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Joined: Jun Sun 15, 2014 5:37 pm
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Location: Montreal, Quebec
I've never tried one. From the schematic, it will tell you polarity (whether NPN or PNP) and a go/nogotest.

It won't say anything about gain or frequency response, or current capacity. It's a sorter.

You could do the same with a DMM, but this does "the lead switching" automatically.

Once I had a meter, there was never a time when that wasn't good enough. I never went through piles of transistors at one time.


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 1:08 am 
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Why bother with something like that when the little cheap Chinese multipurpose tester does the same and much more?


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 2:45 am 
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Joined: Nov Thu 22, 2007 11:31 pm
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Location: Johnston, Iowa
I've got one of those cheap Chinese testers and it works great but not in circuit. While not being able to measure gain this design supposedly can detect open or shorted transistors in-circuit. It seems like that could be useful.


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 7:02 am 
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Location: Corinth, TX
https://archive.org/details/PopularElec ... 3/mode/2up
Page 106

John


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 9:35 am 
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Location: SoCal, 91387
keith49vj3 wrote:
While not being able to measure gain this design supposedly can detect open or shorted transistors in-circuit.

A DMM, VTVM or even a VOM can in most cases do the same functions.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 11:58 am 
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Location: Stone Mountain, GA
Back in High School, I made one similar but I used a quad opamp.

Two opamps were set up as oscillators. One was at 300hz, the other was at about 1 hz. Another inverted the 300hz.
The LED's and transistor set up in series between the 300hz and inverted.
The 1Hz was fed through the resistor to the base.

The LED's would tell if it was PNP or NPN. If it flashes at 1 Hz, it is good. LEDs stay on, transistor shorted. No LED's open.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 4:14 pm 
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Location: Long Island NY
From the looks of it, all this will do is tell you if a transistor is open or shorted, NPN or PNP. It won't tell you anything about leakage or gain so it is not a complete tester in my opinion. I agree that one of those little Chinese PIC micro component testers would be more useful--and I don't even think those are as good as transistor testers which apply realistic voltages and currents to the devices being tested.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 5:20 pm 
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Joined: May Tue 30, 2006 4:46 pm
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Location: Santa Rosa, CA
I agree with Chris and other posters. My little GM328 is great for sorting transistors, and most other components. It's not a "tester" in the sense that it does not apply realistic voltages.

But NO tester can apply realistic conditions "in-circuit." Many times there are other components connected to the device-under-test (DUT) that will distort the results. Also, if the circuit uses a transistor rated for 40 Volts, but the circuit was designed around 9 Volts, applying 40 Volts might just kill other components.

It's tedious, but lifting most of the leads is the only way to get the status of a component.

Image

The GM 328 is cheap and far more informative than two blinking LEDs.

Rich


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 10:20 pm 
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Joined: Nov Thu 22, 2007 11:31 pm
Posts: 1006
Location: Johnston, Iowa
Quote:
But NO tester can apply realistic conditions "in-circuit." Many times there are other components connected to the device-under-test (DUT) that will distort the results. Also, if the circuit uses a transistor rated for 40 Volts, but the circuit was designed around 9 Volts, applying 40 Volts might just kill other components.

It's tedious, but lifting most of the leads is the only way to get the status of a component.

This is what I should have asked in the first place. So there is no way to test transistors in circuit (other than open/shorted/type)? While cleaning my shop last night I stumbled across a Hickok 217 semiconductor tester that claims to be able to test transistors in circuit. it addition to doing what the above device does the manual claims it"allows detection of most leaky devices...even in circuit". Is this a useless piece of test equipment as well?
Keith


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Mon 06, 2021 10:22 pm 
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Joined: May Tue 30, 2006 4:46 pm
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Location: Santa Rosa, CA
Sorry for the sweeping generalization.

There ARE a limited number of cases where components can be tested "in-circuit." If you have a schematic and understand which peripheral components might influence the results, you can test "in circuit."

However, in many of the above cases, a simple DMM will do the job.

Rich


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Tue 07, 2021 1:57 am 
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Joined: Jun Fri 19, 2009 6:34 pm
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Location: Long Island NY
Rich is right. If you want to know if a transistor meets the parameters on its spec sheet, it is usually necessary to remove it from the circuit and test it appropriately. There are exceptions, for example when you are evaluating the performance of a semiconductor in a piece of prototype equipment or for things like RF and microwave transistors where the most practical tester available is the equipment the transistors are used in. Then you are making specialized measurements, often with specialized test gear.

But more often in repair work we don't really need to know every parameter of a transistor. We just need to know it isn't open, shorted, or excessively leaky, and it has a reasonable amount of gain. These tests can be done with the transistor in-circuit in many cases. The traditional way is to use a VOM or DMM to measure the forward and back resistance of the B-E and B-C junctions, then from C to E which should be open circuit either way. Finally you can forward bias the B-E junction with the meter and then short the collector to the base which should produce a decrease in the resistance reading if the transistor has gain. Many small in-circuit testers put the transistor into an oscillator circuit; it if has gain it will oscillate; a dead transistor won't. Modern PIC component testers feed AC voltages into the various leads of the transistor and attempt to identify it by the results. But the instructions for nearly all transistor testers will tell you that if a device tests bad in-circuit, you should remove it and test it again out of circuit to make sure nothing in the circuit was shunting the transistor too heavily to get a reading.

As for the Hickok 217, there don't appear to be any freebie manuals online and I don't know the instrument myself, but from available pictures it appears to be a tester very similar to the circuit at the top of the thread where they use alternating pulses to identify NPN or PNP, shorted or open, and they go a little further and look at the voltage drop to tell you if it is silicon or germanium. Presumably they are doing something in there to guarantee the transistor has some gain too. But you will notice that they tell you right on the front panel that leakage tests have to be done out of circuit. So the 217 would be fine on a service bench where the purpose is to ferret out dud transistors without unsoldering the whole PC board, but an engineer looking for measurements with hard numbers would not be happy with it.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Tue 07, 2021 2:05 pm 
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Joined: Mar Sat 03, 2007 12:53 am
Posts: 900
Here is a low cost kit which functions in a similar fashion to the popular electronics transistor circuit. https://www.ebay.com/itm/161383317929


Last edited by Alan S on Sep Wed 08, 2021 2:21 pm, edited 1 time in total.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Tue 07, 2021 5:49 pm 
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Joined: Nov Thu 22, 2007 11:31 pm
Posts: 1006
Location: Johnston, Iowa
From what folks say I suppose the Hickok 217 in-circuit tester is also worthless. I'm unable to make sense of the schematic but here it is.
Keith


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HICKOK 217 SCHEMATIC.jpg
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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Tue 07, 2021 6:58 pm 
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Holy MILE WIDE text string. Can someone fix this?? lol.

No the Hickock is not worthless. But no tester can reliably test every transistor while wired into any circuit.
I'd never trust it for more than go-no go that way, and even then they can lie.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Thu 09, 2021 5:27 am 
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Joined: Aug Wed 31, 2011 11:23 pm
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Location: Tucson, AZ
I use a B&K 530, seems to be at least tell good/bad in circuit transistor testing. I have used it several times, I also have other out of circuit semiconductor testers. You use to be able to pick up a working B&K 530 for $60-70, and the 520 for half that. But prices seem to have doubled or tripled.


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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Thu 09, 2021 7:52 am 
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I have a B&K model 960 Transistor Radio Analyst that can test Transistors in circuit to determine if they are functioning, and out of circuit for leakage and beta.

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 Post subject: Re: Transistor tester circuit
PostPosted: Sep Thu 09, 2021 2:33 pm 
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Joined: Mar Sat 03, 2007 12:53 am
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Quote:
I use a B&K 530, seems to be at least tell good/bad in circuit transistor testing. I have used it several times, I also have other out of circuit semiconductor testers. You use to be able to pick up a working B&K 530 for $60-70, and the 520 for half that. But prices seem to have doubled or tripled.


I have a B&K 530 and a B&K 510. The AC powered 530 is good for testing in circuit type and pass/fail and out of circuit for non darlington transistor/fet gain, leakage, and ft. The battery powered 510 is good for testing in circuit type and pass/fail. The AC powered 520 adds leakage testing to the 510; however, the reverse voltage is fixed at 2 volts which will not detect transistors which exhibit excessive leakage at higher voltages.


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