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Old 18th April 2005, 06:16 PM   #1
Giaime is offline Giaime  Italy
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Default MJ15003: counterfeits?

Hello! I've tried some times ago fixing a Marantz 1060. It blew all the new MJ15003 I put in. After changing them to 2N3442, it worked fine.

So I thought about counterfeit transistors, and read that MJ15003 are probably the most commonly faked.

I decided to open up a shorted MJ15003 from the amp and a new 2N3442 that left over because I broked a leg of it.

The cover of the MJ went off easily in a vise, the 2N required the use of a saw. The die in the MJ was covered in white silicone, and it measures 4x4mm, under it there was a little copper disc (I read that the disc must be large about the size of the entire transistor, this one was very small). In the 2N, a device rated for less than the powerful MJ, the die was identical in dimensions, no silicone, and a big copper disc under it. I also become surprised when I saw the little wires connecting the MJ collector to the die. And these can carry 16A? I'm not sure about that... 2N had bigger wires, still giving a reduced max Ic.

Chances that I get counterfeits? They gave me much trouble, as Anatech knows...

(sorry, no pictures of them)
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Old 18th April 2005, 08:13 PM   #2
jaycee is offline jaycee  United Kingdom
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Check em against the pictures on http://sound.westhost.com/counterfeit.htm (at the bottom) - it is highly likely you got fakes though.
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Old 18th April 2005, 08:49 PM   #3
Giaime is offline Giaime  Italy
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Yes, I checked. My die is about the same size of the 2N3055, a bit larger maybe. Still not comparable to the original MJ. But the copper plate under it... it looks funny for a 250W device
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Old 18th April 2005, 09:03 PM   #4
Netlist is offline Netlist  Belgium
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Genuine MJ150xx:

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Old 19th August 2005, 03:32 AM   #5
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This counterfeit transistor problem is becoming a real epidemic.

I propose testing any newly obtained transistors with a jig that would separate a real from a fake.

For example, for an MJ15003 I would test the one thing that sets this transistor apart from others and makes it expensive: the SOAR curve.

Subject the part to simultaneous voltage/current combinations which are just inside the DC SOAR curve of the geniune part. The good will survive, the fake shouldn't.

You need to choose V/A combinations which lie in the moderate current/moderate voltage region (rather than hi V lo A or vice versa.) The near-axis extremes are often well handled by many devices, but it's in the middle of the graph that cheap 3055's will have difficulty. Because the MJ15003 has a more "bulging" SOAR curve in the middle, and cheaper parts are more shallow in that area.

Let me know what you guys think, maybe we can come to a concensus as to a "standard" screening test for fakes.

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Old 19th August 2005, 02:13 PM   #6
EUVL is offline EUVL  Europe
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In my experience, fake (OnSemi or Motorola) MJ15003s or MJ15003 from unknown manufacturers measure totally differently to genuine parts- The latter has a much more linear Ib vs Ic curve.

You would need a high current power supply, function generator, oscilloscope, base and emitter resistor (say 100 ohm and 1 ohm) and a buffer (e.g. BUF634) to perform the test.

The best way to ensure you get genuine parts is to buy direct -- from OnSemi, Fairchild, Linear, ......

Most difficult to locate reliable souce are Toshiba FETs and BJTs. I have also had fake Toshiba's; but they did not escape the linearity test.

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Old 19th August 2005, 03:48 PM   #7
Apex Jr is offline Apex Jr  United States
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I'm trying to locate some of these MJ 15003/4 or
MJ 15015/16 for a customer and have located
some MEV as the manufacturer, just followed the
link to Rod Elliot's page and saw there were fakes
of the 2N 3773 with the MEV name on it. Before buying
these I'd like to know about the company MEV and if
these could be fake. Or experiences with usage of MEV items.
Steve @ Apex Jr.
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Old 19th August 2005, 05:08 PM   #8
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In my part of the world, I am unable to buy direct from the mfr, (unless I buy 1000).

They will send me to a distributor.

One of their most trusted distributors, however, Digi-Key, has been reported to ship counterfeit MJ15003/4 to a reader who was writing about this in a counterfeit semi forum.
So I don't know what to think any more.

Digi-Key will accept returns on semiconductors, if you claim they are fake, so there may be no money loss there, but it still puts the burden of testing on the buyer.

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Old 19th August 2005, 05:44 PM   #9
pdq is offline pdq  United States
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I've always used Allied Electronics


...don't know of any connterfeits from them, but I guess anything's possible.
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Old 20th August 2005, 07:24 AM   #10
Enzo is offline Enzo  United States
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I have been buying all my big MJ series xstrs from Allied for years and never got a bad one. And for you little guys, Allied no longer has a minimum order.
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