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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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12th Jan 2022, 2:13 pm | #1 |
Heptode
Join Date: May 2015
Location: Chatham, Kent, UK.
Posts: 947
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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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12th Jan 2022, 2:27 pm | #2 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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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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12th Jan 2022, 2:52 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,549
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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. |
12th Jan 2022, 3:15 pm | #4 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
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Re: Fake transistors.
These devices are NPN silicon RF power transistors.
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14th Jan 2022, 1:20 pm | #5 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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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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14th Jan 2022, 6:44 pm | #6 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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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. |
14th Jan 2022, 6:56 pm | #7 |
Guest
Posts: n/a
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Re: Fake transistors.
What is a "Capstan transistor"?
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14th Jan 2022, 7:06 pm | #8 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Fake transistors.
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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14th Jan 2022, 11:27 pm | #9 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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Re: Fake transistors.
That transistor is just weird not seen anything like that. Is it a dual gate mosfets ?
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15th Jan 2022, 12:20 am | #10 |
Heptode
Join Date: Jul 2016
Location: Portland, Dorset, UK.
Posts: 870
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Re: Fake transistors.
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15th Jan 2022, 12:36 am | #11 | |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
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Re: Fake transistors.
Quote:
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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15th Jan 2022, 1:13 am | #12 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
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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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15th Jan 2022, 9:49 am | #13 | ||
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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Re: Fake transistors.
Quote:
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15th Jan 2022, 10:43 am | #14 |
Nonode
Join Date: Jun 2010
Location: Spalding, Peterborough, Cambridgeshire, UK.
Posts: 2,851
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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. Rob
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15th Jan 2022, 11:37 am | #15 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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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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15th Jan 2022, 12:23 pm | #16 |
Hexode
Join Date: Nov 2009
Location: Cambridge, Cambridgeshire, UK.
Posts: 489
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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. |
15th Jan 2022, 12:33 pm | #17 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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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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15th Jan 2022, 2:14 pm | #18 |
Dekatron
Join Date: Jun 2005
Location: Warnham, West Sussex. 10 miles south of DORKING.
Posts: 9,145
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Re: Fake transistors.
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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15th Jan 2022, 3:25 pm | #19 |
Heptode
Join Date: Dec 2003
Location: South Yorkshire, UK.
Posts: 900
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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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15th Jan 2022, 6:33 pm | #20 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Fake transistors.
Quote:
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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