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Transistors - faked or failed ones?

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 27 June, 2012 » Transistors - faked or failed ones? « Previous Next »

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atferrari
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Username: atferrari

Post Number: 1237
Registered: 05-2005


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Posted on Saturday, 26 May, 2012 - 09:45 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

There is a lot of 40 transistors marked as:
BC550
C K7A

(no logo)

I spent part of the morning matching them in pairs of similar Vbe for a constant current.They were all tested diode-connected (collector to base). No news here.

When trying to measure Ic for a constant Ib of 0,107 mA, found that no mater what Vb I applied to Rb (or leaving in the air), Ic was a steady 34 mA and transistor was rather warm.

After two hours checking everything, and contradicting what the datasheet shows, I reversed the pins (easy because base is the middle pin) and everything started to be "normal" with an Ic of 25 mA only when +9 V was applied to the base resistor. Otherwise, Ic = 0 mA.

Recalling that my DMM has hFE measurements, I got some credible value of 210 appr only when reversing the pins as above.

Further tests with a LED confirmed that something is going wrong: in the datasheet condtion, if I apply +9V to Rb and then leave it in the air, the LED stays dimly ON.

Reversing pins, LED switches ON and OFF as expected.

Last tests I did just for few of them. I had enough for he day.

Faked or failed ones sent to market expecting an idiot like me buying them?
Agustín Tomás - Buenos Aires - Argentina
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boris
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Username: boris

Post Number: 630
Registered: 05-2005


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Posted on Sunday, 27 May, 2012 - 01:39 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Where did you get them? Did they have a 'CE' mark :-)
Thank you for not breeding.
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terrym
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Username: terrym

Post Number: 1160
Registered: 05-2005

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Posted on Sunday, 27 May, 2012 - 04:35 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

If memory serves me correctly, a lot of the BC series came out in TO-92 and TO-92h configurations.

The difference was that the C-E leads were swapped. It used to be that the transistor with all the legs in line were one type and the ones with the leads in a triangular pattern were the other, all though I think that changed some time ago and it is now pot luck as to which type you get.

TM
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bowden_p
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Username: bowden_p

Post Number: 116
Registered: 01-2006

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Posted on Sunday, 27 May, 2012 - 12:44 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Agustin,
I'm sure I have had TO92 transistors marked the same type, but had different pinouts from different manufacturers. Anyway, now I always check with a meter before using them. Why manufacturers can't agree on a common pinout is odd, after all there are only 3 leads to consider!
I hope you can use the lot you have, regardless of the "datasheet" contradictions.
With regards, Paul.
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atferrari
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Username: atferrari

Post Number: 1238
Registered: 05-2005


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Posted on Sunday, 27 May, 2012 - 01:51 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

After 24 hours of posting about this, I have mixed feelings:

Shame: I should have checked first (but nothing suggested it was necessary not even convenient!).

Relief: further testing showed that they seem to be OK; even a batch of good 2N3904 behave the same as these.

Frustration: I am a faithful believer of RTFM. This time, after reading no less than six or seven datasheets (all showing one same layout) have these with the terminals swapped.

Concern: In my box I have now BC550's with two layouts.

If my life goes so complicated, I will consider growing water lilies instead. OMG, yesterday I felt angry, because I believed they were really faulty.

Gracias to all for replying!!

(Message edited by atferrari on 27 May, 2012)
Agustín Tomás - Buenos Aires - Argentina
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vlf
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Username: vlf

Post Number: 325
Registered: 10-2005


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Posted on Sunday, 27 May, 2012 - 02:02 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Interesting... I recently had a batch of BC550C PH58: and too found this problem, but only some were reversed from the normal configuration, these had pre-formed leads C/E spaced out in-line with the Base... not sure who these were purchased from now.

Regards, Brian L.
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basementboy
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Username: basementboy

Post Number: 6
Registered: 05-2012

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Posted on Monday, 28 May, 2012 - 11:21 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I've had exactly the same issue with 2n2222. I was repairing a UPS which had toasted about 10. Bought the replacements from farnell, and for some reason decided to test them before install. C/E reversed. The datasheet for the toasted ones was correct, the datasheet for the new ones from farnell, different manufacturer, was also correct.
I think I'll be paying more attention and test everything in future.

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