Maker Pro
Maker Pro

Testing a NPN Darlington Transistor

ADRT

Nov 25, 2014
192
Joined
Nov 25, 2014
Messages
192
I'm testing a NPN Darlington transistor to see if it is OK. Transistor is for an electronic ignition system on an ATV. Transistor marking ETD41-035. I'm using a Fluke 179 true RMS meter on the diode test setting. Here are the readings I'm getting.

B-C: .543 vdc
B-E: .639 vdc
C-B: infinite
E-B: 1.54 vdc

So going by the test procedure I should be seeing infinite E-B correct?
 

dorke

Jun 20, 2015
2,342
Joined
Jun 20, 2015
Messages
2,342
Unless...
It is not a "pure Darlington".i.e has internal B-E resistors ,TIP120 like.
 

ModemHead

Dec 2, 2010
69
Joined
Dec 2, 2010
Messages
69
The readings would be consistent with a functional Darlington that has bias resistors and a CE protection diode. Random example (2SD2014):
Darlington.png
 

ADRT

Nov 25, 2014
192
Joined
Nov 25, 2014
Messages
192
Unfortunately I can not find the datasheet or any information. Just found a thread on another forum in which the gentlemen stated the same, but was given an alternative transistor to replace with. The replacement worked in his case, and was also being used in an electronic ignition system.
 

ADRT

Nov 25, 2014
192
Joined
Nov 25, 2014
Messages
192
Personally I think the ECM is fine. I helped my cousin troubleshoot a similar problem with his ATV and it turned out to be the stator. This one was removed by a colleague and handed to me to try and fix. I can't find anything wrong with it.
 

Old Steve

Jul 23, 2015
734
Joined
Jul 23, 2015
Messages
734
Personally I think the ECM is fine. I helped my cousin troubleshoot a similar problem with his ATV and it turned out to be the stator. This one was removed by a colleague and handed to me to try and fix. I can't find anything wrong with it.
Just in case it does turn out to be bad, MJE5740 or MJE5742 are recommended replacements, according to this:-
http://www.hondashadow.net/forum/908215-post12.html
 

dorke

Jun 20, 2015
2,342
Joined
Jun 20, 2015
Messages
2,342
Since your measurements revile there is no C-E reverse diode.
A better equivalent replacement should be this one :
ST901T
 

dorke

Jun 20, 2015
2,342
Joined
Jun 20, 2015
Messages
2,342
ADRT,
good find,but...
In this case your original darlington can actually be good.
Best thing would be to build a simple test circuit for it .
like this:
closing the switch should light the led(a 20ma led) .

Voltages on the darlington should be about:
VCE=0.9V
VBE=1.4V

Darlington tester.jpg
 

ModemHead

Dec 2, 2010
69
Joined
Dec 2, 2010
Messages
69
ModemHead said that there is a reverse diode.

My bad, I used weasel words (like a politician) "is consistent with".

Strictly speaking, no E-C measurement was included, and even if there was, with bias resistors, a diode, and the B-C junction, there would be two current paths from E to C, so it would be hard to *absolutely* confirm the presence of the diode.
 

Old Steve

Jul 23, 2015
734
Joined
Jul 23, 2015
Messages
734
My bad, I used weasel words (like a politician) "is consistent with".

Strictly speaking, no E-C measurement was included, and even if there was, with bias resistors, a diode, and the B-C junction, there would be two current paths from E to C, so it would be hard to *absolutely* confirm the presence of the diode.
I was going to add that a C-E test in both directions was a good idea.

And note my weasel-words- I didn't say "there is a reverse diode". Instead I quoted you. :D
 

dorke

Jun 20, 2015
2,342
Joined
Jun 20, 2015
Messages
2,342
ModemHead,
You are correct ,there is no C-E measurement!
I jumped to the conclusion(Freudian?) that the "infinity" was of E-C :oops:.

ADRT,
can you please test the E-C bidirectionally and post?
 

ModemHead

Dec 2, 2010
69
Joined
Dec 2, 2010
Messages
69
Thinking further (a sometimes dangerous thing), if the diode is *not* present, an E-C diode-test reading should be above the reasonable range for a diode forward voltage, due to the bias resistor drop in addition to the B-C junction drop. (A Fluke 179, like many DMMs, uses an approximate 1mA test current.) So a "reasonable" diode forward voltage reading in the E-C direction should confirm the diode is there.
 

ADRT

Nov 25, 2014
192
Joined
Nov 25, 2014
Messages
192
So, E-C: .525, C-E: infinite. So there is a diode.
 

ADRT

Nov 25, 2014
192
Joined
Nov 25, 2014
Messages
192
ADRT,
good find,but...
In this case your original darlington can actually be good.
Best thing would be to build a simple test circuit for it .
like this:
closing the switch should light the led(a 20ma led) .

Voltages on the darlington should be about:
VCE=0.9V
VBE=1.4V

View attachment 22229
I'm going to try this test circuit this evening just to cover all my bases. Personally I hate working on the components of a machine without actually testing it in place myself. I think he has other problems.
 

ADRT

Nov 25, 2014
192
Joined
Nov 25, 2014
Messages
192
So tested this in circuit and it tested fine. Talked to the gentleman about it and sure enough he actually didn't check the stator coils as I suspected. Thanks for all the help guys. :)
 
Top