Fake *******ING "MOTOROLA" Transistors - Page 15 - diyAudio
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Old 3rd April 2006, 04:23 AM   #141
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Just forgot !

Read this and cry... heheheh

I was in a components store, and just to play with those fools I asked for 2N3055... They brought to me a TOSHIBA hahahaha... Then I said,

Dude, its FAKE !

Nooooo, it's NOT !

God... Toshiba do not manufacture this transistor since year 2000 !!

You're completely wrong... You BORN YESTERDAY... I know if the transistor is fake or not at first sight !

IT IS FAAAAKEEEEEEEEEEEE !!!! You don't know anything about transistors !!


Then I left the store
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Old 3rd April 2006, 06:20 AM   #142
ECS21 is offline ECS21  Canada
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Nando,
if you have a capacitance meter,you can check the capacitance between the transistor's B and E. Capacitance should be around
2 to 3 nanoFarads because of their larger die size.Good luck hunting.......

Ecs21,
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Old 3rd April 2006, 01:46 PM   #143
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nando:

The capacitance test is probably the simplest and most portable you can do.

When we discussed hfe, it was the ability of a genuine transistor to maintain a high hfe (20-30) up to high currents. That test is not portable because you'd need to carry around with you the ability to drive 10 or 20 A into the part.

The cap test has its pitfalls though. For my MJ15003's fake parts had between 1500 and 2100 pf, while good parts were between 3400 and 4200pf.

I think instead of setting screening rules based on absolute capacitance, you'd be safer to bring a KNOWN good part along and compare relative cap. The fake should have about half the cap or so of the good one.

And you need to make sure youconnect the + of cap meter to Emitter for an NPN part and vice versa, so as not to forward bias the transistor. If your cap meter doesn't indicate its + lead you have to determine with a voltmeter.

PS. you cannot conclusively condemn the merchant who has Toshiba 2n3055's, since it's not unusual for semiconductors to float around in the market for 5 years, 10 years, or more.

And what exactly are you trying to accomplish by confronting the merchant with an accusation?
I would think that if you take your cap meter in there and get a bad reading, you'd say " I'm sorry, this part doesn't match my requirements, do you have any other batch?" He might then bring out some good ones. It's probably more useful than banning yourself from that store (and many others) forever.



Andy
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Old 3rd April 2006, 01:56 PM   #144
anatech is offline anatech  Canada
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Once you get to know the "norms" of your parts, testing Hfe and capacitance will be a very good indicator. General package appearance will be your first clue, and the manufacturer. Finally, once you know your sources are reliable you will run into very few fakes

-Chris
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Old 3rd April 2006, 02:10 PM   #145
sam9 is offline sam9  United States
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Quote:
General package appearance will be your first clue, and the manufacturer.
Yes, but just to add some irony to the situation -- for some transistors the fakes have a nicer looking package and more legible markings than the real ones.
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Old 3rd April 2006, 02:12 PM   #146
anatech is offline anatech  Canada
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True, but they are still different. that's my point.

-Chris
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Old 3rd April 2006, 09:33 PM   #147
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For those who need a reference range for Cbe values, here's what I tested on a few transistors ( in nF, 5 devices of each ).

MJL4281
11.45
11.03
11.81
11.07
12.08

MJL4302
10.94
10.95
10.94
10.99
10.92

MJ15004
3.67
3.62
3.66
3.68
3.66

MJ15003
3.82
3.65
3.98
3.87
3.84

MJ21193
8.40
8.39
8.40
8.43
8.29

MJ21194
6.42
6.03
5.91
6.40
6.05

MJ21294
13.18
11.73
12.14
12.55
12.62

Looks like every audio power transistor that came out after the 15003, has grossly greater capacitance. Must be the newer technology, higher hfe, and better SOA that's doing this to the Cbe, by imposing a larger die size. Eva did say at one time that Motorola devices have obscenely high cap.


Quote:
General package appearance will be your first clue, and the manufacturer.
Differences in package "look" can and often do occur as a result of devices being made in different periods or different mfr. plants by the same manufacturer. IMHO, not very wise to use that for screening.

Andy
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Old 3rd April 2006, 11:11 PM   #148
Eva is offline Eva  Spain
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Yes, newer On-Semi devices with wider SOA have higher B-E capacitances, and that makes much easier the job of telling genuines from fakes
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Old 3rd April 2006, 11:44 PM   #149
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Ok, ...I'm getting e-mail from people asking for specific part number Cbe values...

1.
What I posted is what I had on hand. I may be able to find others at work, but I can't promise anything.
If anyone else has common audio power transistors available, then maybe they can post Cbe on what they have.
Perhaps we can make a Wiki with this info.

2.
No, there is no complementary to the MJ21294 (although ONsemi has keenly reserved the MJ21293 part number).

The MJ21294 is a dual-die device, two 21194 dies slapped together in parallel. It's in there just for comparison, and it indeed shows exactly twice the cap of the 21194. Complementary symmetry is not the only way to build amps. This device is for quasi-comp designs.


Andy
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Old 4th April 2006, 12:36 AM   #150
ECS21 is offline ECS21  Canada
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pic of fakes motorola transistors
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