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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Jan 2022, 2:13 pm   #1
mickm3for
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Default Fake transistors.

Hi i have taken to testing all new transistors as so many fakes on the market esp RF power types ie 2x mrf485 from uk dealer one reads oc c to b and b to e but 4.6k c to e, the other reads c to b 3.1k and b to e 9k, returning for seller to test . i am glad i did not fit them as i am sure it would have been "you damaged them" ? this is why i always check new transistors if i can Mick
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Old 12th Jan 2022, 2:27 pm   #2
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Default Re: fake transistors

Yes, the MRF transistors are long since out of production by Motorola so are prime candidates for being faked.
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Old 12th Jan 2022, 2:52 pm   #3
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Default Re: fake transistors

If they are MOSFETs they store charge from your meter probes or fingers in the gate capacitance.
They literally "remember" what way your meter probes were last connected between G and S.
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Old 12th Jan 2022, 3:15 pm   #4
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Default Re: Fake transistors.

These devices are NPN silicon RF power transistors.
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Old 14th Jan 2022, 1:20 pm   #5
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Default Re: Fake transistors.

As above there are quite a lot of fake transistors and RF modules in circulation right now. I have been caught several times recently and nearly got totally scammed buying a large quantity from China. I suspect a lot is due to the global electronics shortages. If you don't work in manufacturing you probably wont believe quite how bad things are right now. I have recently gone from paying £4.50 to £45 for a device and this is driving the counterfeit market. So as they say lets be careful out there!
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Old 14th Jan 2022, 6:44 pm   #6
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Default Re: Fake transistors.

Even 10 years ago they were reprocessing pulls to pass off as new.
Capstan transistors with milling lines on the leads and bruising of the mounting holes...
New they were not. Good they were not.
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Old 14th Jan 2022, 6:56 pm   #7
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Default Re: Fake transistors.

What is a "Capstan transistor"?
 
Old 14th Jan 2022, 7:06 pm   #8
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Default Re: Fake transistors.

Quote:
Originally Posted by merlinmaxwell View Post
What is a "Capstan transistor"?
Term usually applies to the type which have 4 leads sticking out from the package at 90-degree intervals and a central stud to attach the thing to its heatsink.

Because it has a passing appearance to an old-fashioned marine capstan used for raising anchors...
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Old 14th Jan 2022, 11:27 pm   #9
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Default Re: Fake transistors.

That transistor is just weird not seen anything like that. Is it a dual gate mosfets ?
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Old 15th Jan 2022, 12:20 am   #10
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Default Re: Fake transistors.

Quote:
Originally Posted by ChristianFletcher View Post
That transistor is just weird not seen anything like that. Is it a dual gate mosfets ?
Don't know what type they are but they are generally to be seen in RF/high frequency devices.
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Old 15th Jan 2022, 12:36 am   #11
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Default Re: Fake transistors.

Quote:
If you don't work in manufacturing you probably wont believe quite how bad things are right now
and in the repair industry!

RS have changed alot of their 'expected in stock in July 2022..' etc dates to 'we are not accepting back orders for these items at the moment'.

There's also a global shortage of electrolytic capacitors
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Old 15th Jan 2022, 1:13 am   #12
emeritus
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Default Re: Fake transistors.

I was using that type of transistor in the early 1970's when designing broadband UHF RF power amplifiers. Two of the opposite leads were soldered to the ground plane, the other two were the input and output, and were soldered to microstrip transmission line sections dimensioned to provide impedance matching from 50 Ohms to the very low complex input and output impedances of the transistors. They often used Beryllium Oxide insulation for good thermal conductivity, safe enough as long as not damaged so as to release dust.
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Old 15th Jan 2022, 9:49 am   #13
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Default Re: Fake transistors.

Quote:
Originally Posted by McMurdo View Post
Quote:
If you don't work in manufacturing you probably wont believe quite how bad things are right now
and in the repair industry!

RS have changed alot of their 'expected in stock in July 2022..' etc dates to 'we are not accepting back orders for these items at the moment'.

There's also a global shortage of electrolytic capacitors
RS have been a dead loss for me. I got a dispatched notice for some ICs that I ordered when the order didn’t arrive I chased them to find out the goods were not dispatched and were out of stock. The apologies I got was a joke. There is so much unavailable right now. I am regularly buying from Didikey and mouser. In fact all my ICs are now coming from mouser in the US.
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Old 15th Jan 2022, 10:43 am   #14
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Default Re: Fake transistors.

Maybe good news for me, as I have a large amount of assorted rf power transistors, mostly bipolar and dating as far back as late 1960s. A few high power fets as well. Definitely not fakes!
Must get round to sorting them out one day.

10 years ago, at work, QA had a right job sourcing genuine semiconductors. They needed to take great care, as even a big supplier could get caught out sometime.
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Old 15th Jan 2022, 11:37 am   #15
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Default Re: Fake transistors.

It’s still not clear to me what’s causing the problem certainly water shortages in the Fab countries is having a major impact. Personally I think it’s just that the manufacturer are choosing to follow the money and supply higher margin product lines. I work in industrial electronics so I’m a bottom feeder of the electronics world.
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Old 15th Jan 2022, 12:23 pm   #16
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Default Re: Fake transistors.

Has anyone ever bought a fake/counterfeit component from a reputable source? Eg: RS , Mouser, Farnell, Digikey etc... not Ebay or Someblokesellstufffromhome Components Ltd.

I would say probably not.

Warning people that "there are fake components out there" is like saying "you can buy bread from Tescos".

Just my opinion.
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Old 15th Jan 2022, 12:33 pm   #17
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Default Re: Fake transistors.

I take the point about reputable sources and of course you are less likely to have problems. But there is also a reputable gray market in electronics and second tier suppliers. I know my contract manufacture has had many issues quite recently with fake chips that work to a fashion and we’re from known suppliers. A lot of us have been accessing the gray market recently as I said I’m paying £45 pounds for a chip that was £4.50 when I bought the last batch 6 months ago.
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Old 15th Jan 2022, 2:14 pm   #18
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Default Re: Fake transistors.

Quote:
Originally Posted by McMurdo View Post
Quote:
If you don't work in manufacturing you probably wont believe quite how bad things are right now
and in the repair industry!

There's also a global shortage of electrolytic capacitors
I'm not surprised there is a shortage of electrolytic capacitors. The shocking failure rate of the miniature aluminium type, writing off millions of pounds worth of equipment has probably got something to do with it. Things can only get worse. John.
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Old 15th Jan 2022, 3:25 pm   #19
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Default Re: Fake transistors.

Only based on discussion with my contract manufacturer last week they told me things are indeed getting worse and no end in sight for now! I suspect like the bog roll buy out there is a lot of panic buying going on. I certainly am panicking buying anything I can right now, no build no company no job it’s that simple. So I have ordered two years stock if and when it ever comes available.
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Old 15th Jan 2022, 6:33 pm   #20
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Default Re: Fake transistors.

Quote:
Originally Posted by ChristianFletcher View Post
That transistor is just weird not seen anything like that. Is it a dual gate mosfets ?
No, it's just a normal bipolar RF power-transistor. Such things have been commonplace since the late-60s days of the Pye Westminster/Europa/Whitehall; the overall design provides two 'legs' at 180-degrees-to-each-other in order to get minimum emitter-impedance-to-ground; the base and collector being the other two legs.

The stud-mounting was to the heatsink. I learned that it was always good to use a torque-wrench when tightening the nut on the stud; over-do it [as one of my competitors was prone to do] and the stud would be stretched-beyond-yield-point, meaning insufficient clamping to the heatsink and sub-optimal heat transfer.
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