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Transistor testing

R

RobH

Guest
I have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see “OL” (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V.4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.

Are mine no good and should I bin them. I have had them for a couple of
years or so now, and only used 1 of them.
 
R

Ralph Mowery

Guest
In article <hca5oiFtbctU1@mid.individual.net>, rob@despammer.com says...
have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see ?OL? (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V.4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.
If you are seeing .02 v it is as if the transistor is shorted. Try
testing in both directions with the meter set as an ohm meter. I assume
you are using a digital meter which usually will not have enough
current/voltage to bias the transistor into conduction. It will
probably show shorted or very near zero ohms in both directions. An
analog meter will usually bias the transistor into conduction so it will
show low resistance in one direction and if the leads are reversed , a
high resistance.

Seems that you are using the meter like a diode tester. That is fine.

For any type of a a bipolar transistor put one lead on the base. Then
put the other lead on the emitter, then the collector. It should show
around .2 to .4 volts if the older germanium and .6 to .9 if silicon.
Then reverse the leads and do the same . The meter should show an open
circuit or OL . Then put the leads on the emitter and collector.
They should show open OL on in both directions.

A common transistor will test like 2 diodes in series or back to back
with the base as the common connection point.
 
R

RobH

Guest
On 04/03/2020 19:22, Ralph Mowery wrote:
In article <hca5oiFtbctU1@mid.individual.net>, rob@despammer.com says...
have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see ?OL? (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V.4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.



If you are seeing .02 v it is as if the transistor is shorted. Try
testing in both directions with the meter set as an ohm meter. I assume
you are using a digital meter which usually will not have enough
current/voltage to bias the transistor into conduction. It will
probably show shorted or very near zero ohms in both directions. An
analog meter will usually bias the transistor into conduction so it will
show low resistance in one direction and if the leads are reversed , a
high resistance.

Seems that you are using the meter like a diode tester. That is fine.

For any type of a a bipolar transistor put one lead on the base. Then
put the other lead on the emitter, then the collector. It should show
around .2 to .4 volts if the older germanium and .6 to .9 if silicon.
Then reverse the leads and do the same . The meter should show an open
circuit or OL . Then put the leads on the emitter and collector.
They should show open OL on in both directions.

A common transistor will test like 2 diodes in series or back to back
with the base as the common connection point.
The meter I am using is an old Fluke77 digital from RS about 30 or 35
years ago, and I have tried x5 BC547 tansistors.
Using the voltage selection, I get 0.0v with negative lead on the
collector and positive on the Emitter, and swapping round I get 0.25v
Using the Ohm selection, I get OL in both directions, and the same using
the diode selection with the negative lead on the base of the transistor

I don't have an analogue meter now.

Thanks
 
A

Arie de Muynck

Guest
On 2020-03-04 21:40, RobH wrote:

The meter I am using is an old Fluke77 digital from RS about 30 or 35
years ago, and I have tried x5 BC547 transistors.
Using the voltage selection, I get 0.0v with negative lead on the
collector and positive on the Emitter, and swapping round I get 0.25v
Using the Ohm selection, I get OL in both directions, and the same using
 the diode selection with the negative lead on the base of the transistor

I don't have an analogue meter now.

Thanks
Well, then your transistors look fine as far as you could test them.

The voltage test is useless, a transistor does not generate a voltage.
What you might see is the diode of the B-E (or C-B) rectifying noise
from the environment. Useless as an indicator.
The ohms range test is also useless, it normally test with 0.2V which is
not enough to bias the diode and will give an OL reading in both
directions. As you properly described.

You _MUST_ use the diode testing range!
The B-E test should be about 0.55V with + on B side, and OL in the other
direction.
Same for the B-C test: about 0.55V with + on B side and OL in the other
direction.
The C-E test should be OL in both directions.

Regards,
Arie
 
R

Ralph Mowery

Guest
In article <hcai1iF1cqgU1@mid.individual.net>, rob@despammer.com says...
The meter I am using is an old Fluke77 digital from RS about 30 or 35
years ago, and I have tried x5 BC547 tansistors.
Using the voltage selection, I get 0.0v with negative lead on the
collector and positive on the Emitter, and swapping round I get 0.25v
Using the Ohm selection, I get OL in both directions, and the same using
the diode selection with the negative lead on the base of the transistor
I may have misunderstood what you said about using the voltage
selection. The diode selectionis what I would have thought you were
using. That puts a voltage on the probes, then reads how much voltage is
dropped across the leads so to speak. The way I remember the first
posting was 0.025 volts. It could have been a typo and you ment the
0.25 which sounds more reasonable.

If you get a voltage (number showing up on the meter readout) with the
leads in one direction and the OL in the other direction while in the
other direction going base to emitter and then base to collector, and OL
in both directions emitter to collector, the transistor is probably
good.

The main thing is not the total number,but a large difference in each
direction with the exception of collector-emitter which should be very
large resistance in both directions or OL in the diode poaition.
 
J

Jasen Betts

Guest
On 2020-03-04, RobH <rob@despammer.com> wrote:
I have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see “OL” (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V. 4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.
You must put your meter in diode-test mode, (on the fluke 77 it looks
like that's also continuity beeper mode) it should say OL with the leads
unconnected and 0.00V with them toucheing eaco other. then do the above
measurements.

Are mine no good and should I bin them. I have had them for a couple of
years or so now, and only used 1 of them.
I'm guessing operator error, they should still be good after only a few
years.

--
Jasen.
 
R

RobH

Guest
On 05/03/2020 05:21, Jasen Betts wrote:
On 2020-03-04, RobH <rob@despammer.com> wrote:
I have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see “OL” (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V. 4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.

You must put your meter in diode-test mode, (on the fluke 77 it looks
like that's also continuity beeper mode) it should say OL with the leads
unconnected and 0.00V with them toucheing eaco other. then do the above
measurements.

Are mine no good and should I bin them. I have had them for a couple of
years or so now, and only used 1 of them.

I'm guessing operator error, they should still be good after only a few
years.
Putting the meter in diode-test mode,it reads OL when leads are
unconnected and 0.00v when touching each other.
Then connecting the positive to the Emitter and negative lead to the
Base the meter beeps, then reads 0.666, the same reading when the
positive is connected to the collector.
 

Guest
On Thursday, 5 March 2020 09:34:30 UTC, RobH wrote:
On 05/03/2020 05:21, Jasen Betts wrote:
On 2020-03-04, RobH <rob@despammer.com> wrote:
I have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see “OL” (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V. 4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.

You must put your meter in diode-test mode, (on the fluke 77 it looks
like that's also continuity beeper mode) it should say OL with the leads
unconnected and 0.00V with them toucheing eaco other. then do the above
measurements.

Are mine no good and should I bin them. I have had them for a couple of
years or so now, and only used 1 of them.

I'm guessing operator error, they should still be good after only a few
years.



Putting the meter in diode-test mode,it reads OL when leads are
unconnected and 0.00v when touching each other.
Then connecting the positive to the Emitter and negative lead to the
Base the meter beeps, then reads 0.666, the same reading when the
positive is connected to the collector.
that means the tr is dropping 0.666v as each junction conducts. Black lead is +ve on diode test so you have an npn tr behaving normally.


NT
 
R

RobH

Guest
On 05/03/2020 10:39, tabbypurr@gmail.com wrote:
On Thursday, 5 March 2020 09:34:30 UTC, RobH wrote:
On 05/03/2020 05:21, Jasen Betts wrote:
On 2020-03-04, RobH <rob@despammer.com> wrote:
I have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER (E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see “OL” (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V. 4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a few of
what I have, and not 0.45V.

You must put your meter in diode-test mode, (on the fluke 77 it looks
like that's also continuity beeper mode) it should say OL with the leads
unconnected and 0.00V with them toucheing eaco other. then do the above
measurements.

Are mine no good and should I bin them. I have had them for a couple of
years or so now, and only used 1 of them.

I'm guessing operator error, they should still be good after only a few
years.



Putting the meter in diode-test mode,it reads OL when leads are
unconnected and 0.00v when touching each other.
Then connecting the positive to the Emitter and negative lead to the
Base the meter beeps, then reads 0.666, the same reading when the
positive is connected to the collector.

that means the tr is dropping 0.666v as each junction conducts. Black lead is +ve on diode test so you have an npn tr behaving normally.


NT
Thanks, and by accident I found that the transistor is working correctly.
I have put together a IR circuit with transmiter led and and photo
diode, using x2 transistors and a 555. I couldn't get to work until a
wire from the ground rail of a breadboard touched a leg of a 220ohm
resistor. Then, for some unknown reason, it works in reverse!!
 
R

RobH

Guest
On 05/03/2020 11:17, RobH wrote:
On 05/03/2020 10:39, tabbypurr@gmail.com wrote:
On Thursday, 5 March 2020 09:34:30 UTC, RobH  wrote:
On 05/03/2020 05:21, Jasen Betts wrote:
On 2020-03-04, RobH <rob@despammer.com> wrote:
I have some BC547 transistors which I want to use in a circuit, but
according to this:

Hook the positive lead from the multimeter to the to the EMITTER
(E) of
the transistor. Hook the negative meter lead to the BASE (B) of the
transistor. For an good NPN transistor, you should see “OL” (Over
Limit). If you are testing PNP transistor, the meter should show a
voltage drop between 0.45V and 0.9V. 4 May 2017

None of the BC547's give the those readings, as I get 0.02V on a
few of
what I have, and not 0.45V.

You must put your meter in diode-test mode, (on the fluke 77 it looks
like that's also continuity beeper mode) it should say OL with the
leads
unconnected and 0.00V with them toucheing eaco other. then do the above
measurements.

Are mine no good and should I bin them. I have had them for a
couple of
years or so now, and only used 1 of them.

I'm guessing operator error, they should still be good after only a few
years.



Putting the meter in diode-test mode,it reads OL when leads are
unconnected and 0.00v when touching each other.
Then connecting the positive to the Emitter and negative lead to the
Base the meter beeps, then reads 0.666, the same reading when the
positive is connected to the collector.

that means the tr is dropping 0.666v as each junction conducts. Black
lead is +ve on diode test so you have an npn tr behaving normally.


NT


Thanks, and by accident I found that the transistor is working correctly.
I have put together a IR circuit with transmiter led and and photo
diode, using x2 transistors and a 555. I couldn't get to work until a
wire from the ground rail of a breadboard touched a leg of a 220ohm
resistor. Then, for some unknown reason, it works in reverse!!
Update:
The circuit works correctly now, as I swapped another transistor, and
put in the wrong way round, Doh!
 
B

Bob Engelhardt

Guest
For 8 bux, one of these component testers would be good for your fooling
around ... er ... experimenting:
https://tinyurl.com/t4dbroz
 
R

RobH

Guest
On 06/03/2020 01:01, Bob Engelhardt wrote:
For 8 bux, one of these component testers would be good for your fooling
around ... er ... experimenting:
https://tinyurl.com/t4dbroz
Thanks, but we don't do bux in the UK.
 
J

jfeng@my-deja.com

Guest
On Friday, March 6, 2020 at 12:41:09 AM UTC-8, RobH wrote:
On 06/03/2020 01:01, Bob Engelhardt wrote:

For 8 bux, one of these component testers would be good for your fooling
around ... er ... experimenting:
https://tinyurl.com/t4dbroz

Thanks, but we don't do bux in the UK.
It is also available on eBay. Some are Chinese sellers, so if they ship to the US, they probably also ship to the UK.

Do you get PE (formerly Everyday Practical Electronics)? Available from your favourite bookshop for ₤5. For the past few years, they have had a series of articles on how much they like the cheap electronics modules that are coming out of China; they may even have reviewed this tester. Also, the March 2020 issue has an article on how to build your own Arduino-based graphical diode tester.

Having said all that, I suggest that you rig up your own with a 9v battery and a 10K resistor (values not critical, and +/- 50% will work OK). Wire in series and apply to your diode (or two of the transistor leads) and measure the voltage across the DUT. This is simple enough that you will eventually learn what to expect and why. After you have some e practice, try changing the resistor value and/or the battery voltage to see how that changes the answer. To me, the fancy test devices are like using the OBD when the check engine light comes on: the diagnostic may be meaningful to those with skills and experience, but can be gibberish to the uninitiated.
 
R

Ralph Mowery

Guest
In article <c1fd1d6a-920c-48d8-80a4-af35ff292a32@googlegroups.com>,
jfeng@my-deja.com says...
Thanks, but we don't do bux in the UK.

It is also available on eBay. Some are Chinese sellers, so if they ship to the US, they probably also ship to the UK.

Do you get PE (formerly Everyday Practical Electronics)? Available from your favourite bookshop for Ł5. For the past few years, they have had a series of articles on how much they like the cheap electronics modules that are coming out of China; they may even have reviewed this tester. Also, the March 2020 issue has an article
on how to build your own Arduino-based graphical diode tester.

Having said all that, I suggest that you rig up your own with a 9v battery and a 10K resistor (values not critical, and +/- 50% will work OK). Wire in series and apply to your diode (or two of the transistor leads) and measure the voltage across the DUT. This is simple enough that you will eventually learn what to expect and
why. After you have some e practice, try changing the resistor value and/or the battery voltage to see how that changes the answer. To me, the fancy test devices are like using the OBD when the check engine light comes on: the diagnostic may be meaningful to those with skills and experience, but can be gibberish to the
uninitiated.
Here is one for 12.49 pounds or what ever that funny looking L is in the
UK. It is in a nice caes and has leads . You can get them for about 7
pounds out of the case and probably no leads.


https://www.ebay.co.uk/itm/1-8-Rechargeable-IR-Decoder-TFT-Transistor-
Tester-Electronic-Component-LCR-TC1/274263027966?
hash=item3fdb59b0fe:g:G-sAAOSwsCdeQ83Q

They are mainly the same as the Peak testers that sell for around $ 100
US. Not sure what that would be in Pounds or Euros. Probably somewhere
in the general price range.

If one can not understand what these testers display, they should
probably not be messing with the electronics at the component level.
All you do is hook up any of the 3 leads to a device and look at the
screen. It will tell you what leads are connected and the value of the
component.

That is a lot different than the car computers. They do not actually
test a specific component to see if it is good or bad or the parameters
of it. Just like the tire pressure sensor on some of the cars. The
warning light will come on,but not tell which tire or what the pressure
is or if the sensor is bad or not. Some cars do tell the pressure of
the individual tires, but will not tell if the shown pressure is
accurate or not.
 
R

RobH

Guest
On 06/03/2020 15:29, Ralph Mowery wrote:
In article <c1fd1d6a-920c-48d8-80a4-af35ff292a32@googlegroups.com>,
jfeng@my-deja.com says...

Thanks, but we don't do bux in the UK.

It is also available on eBay. Some are Chinese sellers, so if they ship to the US, they probably also ship to the UK.

Do you get PE (formerly Everyday Practical Electronics)? Available from your favourite bookshop for Ł5. For the past few years, they have had a series of articles on how much they like the cheap electronics modules that are coming out of China; they may even have reviewed this tester. Also, the March 2020 issue has an article
on how to build your own Arduino-based graphical diode tester.

Having said all that, I suggest that you rig up your own with a 9v battery and a 10K resistor (values not critical, and +/- 50% will work OK). Wire in series and apply to your diode (or two of the transistor leads) and measure the voltage across the DUT. This is simple enough that you will eventually learn what to expect and
why. After you have some e practice, try changing the resistor value and/or the battery voltage to see how that changes the answer. To me, the fancy test devices are like using the OBD when the check engine light comes on: the diagnostic may be meaningful to those with skills and experience, but can be gibberish to the
uninitiated.



Here is one for 12.49 pounds or what ever that funny looking L is in the
UK. It is in a nice caes and has leads . You can get them for about 7
pounds out of the case and probably no leads.


https://www.ebay.co.uk/itm/1-8-Rechargeable-IR-Decoder-TFT-Transistor-
Tester-Electronic-Component-LCR-TC1/274263027966?
hash=item3fdb59b0fe:g:G-sAAOSwsCdeQ83Q

They are mainly the same as the Peak testers that sell for around $ 100
US. Not sure what that would be in Pounds or Euros. Probably somewhere
in the general price range.

If one can not understand what these testers display, they should
probably not be messing with the electronics at the component level.
All you do is hook up any of the 3 leads to a device and look at the
screen. It will tell you what leads are connected and the value of the
component.

That is a lot different than the car computers. They do not actually
test a specific component to see if it is good or bad or the parameters
of it. Just like the tire pressure sensor on some of the cars. The
warning light will come on,but not tell which tire or what the pressure
is or if the sensor is bad or not. Some cars do tell the pressure of
the individual tires, but will not tell if the shown pressure is
accurate or not.
That same tester is Ł20.59 on Amazon uk with nearly 500 reviews.

Thanks
 
J

Jasen Betts

Guest
On 2020-03-06, Ralph Mowery <rmowery28146@earthlink.net> wrote:
In article <c1fd1d6a-920c-48d8-80a4-af35ff292a32@googlegroups.com>,
jfeng@my-deja.com says...

Thanks, but we don't do bux in the UK.

It is also available on eBay. Some are Chinese sellers, so if they ship to the US, they probably also ship to the UK.

Do you get PE (formerly Everyday Practical Electronics)? Available from your favourite bookshop for ÂŁ5. For the past few years, they have had a series of articles on how much they like the cheap electronics modules that are coming out of China; they may even have reviewed this tester. Also, the March 2020 issue has an article
on how to build your own Arduino-based graphical diode tester.

Having said all that, I suggest that you rig up your own with a 9v battery and a 10K resistor (values not critical, and +/- 50% will work OK). Wire in series and apply to your diode (or two of the transistor leads) and measure the voltage across the DUT. This is simple enough that you will eventually learn what to expect and
why. After you have some e practice, try changing the resistor value and/or the battery voltage to see how that changes the answer. To me, the fancy test devices are like using the OBD when the check engine light comes on: the diagnostic may be meaningful to those with skills and experience, but can be gibberish to the
uninitiated.



Here is one for 12.49 pounds or what ever that funny looking L is in the
UK. It is in a nice caes and has leads . You can get them for about 7
pounds out of the case and probably no leads.


https://www.ebay.co.uk/itm/1-8-Rechargeable-IR-Decoder-TFT-Transistor-
Tester-Electronic-Component-LCR-TC1/274263027966?
hash=item3fdb59b0fe:g:G-sAAOSwsCdeQ83Q
Ha! That's a different sort of "Tube" circuit in the background.

--
Jasen.
 
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