In circuit transistor tester

[mixos1]

This circuit i build from a kit , that i brought some time ago from dicksmiths electronics, really has it uses the circuit may work by shorting out the leds, so some one tells me, and so i posted this for all to share.

by Steven (received via e-mail)

 

[steven2]

here is the in circuit transistor tester

View attachment 35772

 

[hotwaterwizard2]

NICE

 

[audioguru2]

Hi Steven,
Yeah, that's a good one.
Is that a solid metal case?

I have heard that many transistors have some gain when their emitter and collector leads are backwards. What does your tester do then? Does the LED dim only a bit or completely?

 

[steven2]

thanks hot water wizard and audio guru its a nice pastic box with metal pannel at front with the 2 leds and switch the circuit box has the leads runing out the top end for the base ,emmitter and collector. so with the push down clips its easy to attach to the transister legs . at the top end of the plastic circuit box where the wires run out, the b for base and e for emmitter and c for collector are there so youll know which wires with the push clips go to what legs of the transister.

 

[steven2]

audio guru the leds blink acording to the condition the transistor is in. look at the panel on the on the picture of the in circuit transister tester. it will show you . the white dots are for when the leds blink to indicate , wheather there npn or pnp and which legs are faulty arcording to the blinking lights. something like that.

 

[audioguru2]

Hi Steven,
Yes, I understand that a transistor that is good will turn-off its blinking LED. But I think that your transistor tester will also show that a faulty transistor with a very low gain is good.
To simulate a transistor that has a very low gain, please test a good BC548, 2N3904 or 2N2222 with its emitter and collector leads reversed. Then let us know if its LED dims a bit or turns-off completely. Please try it with a PNP transistor too.

 

[hotwaterwizard2]

Here is my little (OUT OF CIRCUIT) Collection.

View attachment 35778

 

[steven2]

hotwater wizard cool. im planing on getting another transister tester soon , this one allso dose scrs to acording to the info on it in my altronics catalouge.

 

[Dido]

Look at that one The design shown will test PNP and NPN transistors, diodes and SCRs both "in-situ" (equipment of course de-energised) and also by direct connection to a stand-alone component. It is a simple GO/NOGO test which can identify diode and transistor action and will indicate diode polarity and transistor type PNP/NPN, if this is unknown.

View attachment 35780

 

[audioguru2]

Hi Hotwaterwizard,
Your 1st and 2nd transistor tester circuits are great and easy to make.
Sorry, but in the 3rd one, it tests the two transistor junctions separately, not like a transistor that normally has a reversed-biased C to B junction. Without any current-limiting, the transistor's base and/or the LEDs may blow. If the transistor is shorted, the LEDs will blow. If you accidently press both buttons without a transistor connected, say goodbye to all LEDs. ;D It uses a lot of batteries.
The 4th tester has an emitter-follower for the PNP, but a common-emitter for the NPN. Maybe both should be the same.