counterfiet sa1943's ??

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#83
Since there's such a counterfit problem with the Toshiba transistors, wouldn't it be wise to replace them with On-Semi transistors of similar rating. Like MJL 4281/4302 or MJL 21196/95 because you can get them right from On-Semi and be 100% sure they are real devices.
 
#86
sam9 said:
Oh yes, I've read of counterfeit Onsemi's turning up too. Eastern Europe I think.

This suggests you can't just assume one brand or another is safe. You really have to consider the source.
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I see, it's the source.

Wonder why the die is so small in the bad ones. DId they take a To-220 Transistor die or something and put it in the TO 247 case? Makes me wonder how they even expect them to pass as a real one when they blow up when you first put them in the amp. I guess just a quick buck on a one time purchase is what these counterfeiters are trying to achieve.
 
#87
They will pass a simple low voltage go-nogo test. They may even pass a more sophisticated test such as you might administer with a Sencore Cricket although there are things to look for. An output BJT with a beta of 200+ should make you suspicious -- but of course the crooks my get smart enough an use chips from lower perfomance small sig device.

Makes me wonder how they even expect them to pass as a real one when they blow up when you
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The bad guys are long gone before this happens. The distributors smaller distributors who make a living buying reselling excess inventory from from unverified sources are part of the problem. They will either not return calls or e-mails or just claim it must have been something you did. I've dropped a couple from my list of vendors I deal with for such BS.
 
#88
A photo of 100% genuine 2SA1943 & 2SC5200 >>>
Sorry about the bad quality of the photo-increase the brightness of your monitor to see it as well
 

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#89
Eva said:
Obtaining different capacitance values depending on the polarity means that your capacitor tester is applying some DC

Try to filter out the DC using something 10uF in series with the capacitor tester a 1Megohm in paralell to the junction of the transistor

The other problem may be your capacitor tester using a too high test voltage [>500mVpp]. This is harder to circumvent but placing 1nF or 2.2nF in series with the juction to attenuate te measuring signal may work, but then you have to calculate the effective capacitance of the juction based on the measurement [for series capacitors : 1/C_measured = 1/C1 + 1/C2]

My capacitor tester [Monacor LCR-4000] works fine for transistors and diodes because it uses no DC [internally AC coupled] and the test signal is a 600mV p-p sine wave [not enough to turn on the juction diodes]

EDIT : You made a little mistake when measuring, the capacitances you have to measure are C-B and E-B, not C-E
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Hi Eva,

I bought some 2SA1302 and 2SC3281 (4 each) last June (2005). I had eMail communications with a few people suggesting I had to crack open or blow the device to see if they were fake. I bought these devices after researching what I could find at time not knowing about the capacitance based testing for die size I discovered of this thread with your comments to check capacitance.

Sadly due to circumstances beyond my control my phone line (internet with it) went dead for 3 months starting 26 Jul 2005. I clearly had no internet access, but also chaling the Bell company to fix this problem of no 51V on my line was a full time job. The aftermath has kept me in a backlog ever since.

I have now just started finding the articles and threads with your comments I had seen just before my internet died with my phone line last July. I know I had the same experience with different capacitance depending on polarity and also observed one needed to let the stored charge disapate before taking a second or different pair of lead capacatance. That was what I knew as of last July.

Fast forward to tonight and I took my capacatance meter and checked for DC based on your comments of aonter person's experiences. A number of rangers have over 1V DC and another set of ranges vary from 0.8VDC to 0.4VDC. I tried a HP 973A for DC and it does as well, about 600mVDC if my memory recalls correctly. I have a HP digital function generator. Is there a simple circuit I can make to use the HP function generator to measure capacitance for these devices? If you feel your suggestions you made to remove DC are perfered, can you post a simple schematic of what you were describing? I did not understand what the words were describing so I could translate what seems a very simple circuit to use with a capacitance meter that has DC.

Thanks in advance.

Regards,

John L. Males
Willowdale, Ontario
Canada
27 April 2006 02:00
27 April 2006 02:07 As usual typo corrections. Sorry
 
#90
more fakes and capacitance

well my good forum friends check this out ....
my cap meter is a cheap kt cap meter

with black on C of 2sc3281 which i know for sure its original and red on B i mesure 19.7nf

performing the same test to a 2sa1943 which i thing is a fake i get 785pf!!!!!!!!

reverrsing the polarity on the fake 1943 has just a few more pf .....thanks for the info sounds good!!!!


once ive met one amp made in germany using 2x bd249 and 2x bd 250 per chanel ...very stable 100w@8ohm it sounded very musical but at the times i was to inexpirienced to tell more about the quality ......GOOD OLD TIMES ....
 
#92
I know this is probably a worn out thread but my curiosity got the better of me when I came across the method used to determine a fake from a genuine transistor. I decided to test 10 of each 2SA1943, 2SC5200 and OnSemi devices that I bought directly from OnSemi and tabulated my results.

You will notice 2SA1216 and 2SC2922 results as well. These two are known fakes that I never bothered using after checking out the ESP article on counterfeit transistors.

The device I used for testing is a Toptronic T24 LCR meter that test caps in the range 200pF - 2uF @1kHz and is claimed to be accurate to 1%.

Comments anyone?
 

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