NEC 2SC3840/2SA1486 Possible fakes ? - Page 1
Forum section: electronics / general

author: M4trix
author_rank: Frequent Contributor
timestamp: November 04, 2022, 08:30:32 pm
content: Hi guys.I know, the rule of thumb is to avoid Alitard when it comes to obsolete transistors !But ! The picture on sellers site is showing NOS NEC 2SC3840/2SA1486. Well, you know the typical transistors from that period, plastic black/green TO-126 case with silverish painted markings on a rough/mat surface. Something like this -->But what I received is this -->As you can see. Markings are made with a laser on a shiny surface. The NEC logo on 2SA1486 is missing ! Mind boggling situation. The back plate is a typical NEC transistor shape. You probably already know that Renesas took over NEC business back in 2010 and they continued to manufacture 2SC3840/2SA1486 for some time. You can even still buy them at Digikey but the minimum order is 345 pieces. Does anyone have a picture of these transistors made by Renesas btw ? I also did some hfe and Vceo (breakdown voltage) tests -->2SA1486Vceo - 730VDChfe - 60hfe category - L2SC3840Vceo - 720VDChfe - 90hfe category - KSo, according to NEC datasheets, these values are in the specified range. So guys, would you be so kind and share with me you opinions. Cheers.

author: wraper
author_rank: Unknown
timestamp: November 04, 2022, 08:52:35 pm
content: Terminals of A1486 are suspicious. Looks as if they could be used parts with new terminals welded on. Green plastic usually is an indication of pre-90's Japanese components. Later they transferred to black plastic.QuoteHow did you measure hfe? Sticking into some cheap meter will not give you a proper reading to compare with datasheet. It needs to be done with specific conditions written in the datasheet to be directly comparable.Overall the vast majority of transistors an Aliexpress are counterfeits, especially from cheap deals. But paying as much as from reputable distro, does not guarantee a genuine part either.

author: wraper
author_rank: Unknown
timestamp: November 04, 2022, 08:57:32 pm
content: QuoteIt's a marketplace item from Rochester which sells obsolete components.

author: M4trix
author_rank: Frequent Contributor
timestamp: November 04, 2022, 09:41:52 pm
content: Hi,I did the quick tests with ermm...cough.... DY294 transistor tester. Not high end equipment but it's doing a fair job for the price.The problem is that all manufacturers ditched the high voltage (Vceo 600-700V), high speed transistors in a TO-126 case. These transistors are quite good for VAS and pre-drivers in audio amplifiers. Yamaha used them in their TXn series. Btw, ON Semi is still making KSA1156/KSC2752 but the hfe differences is huge, almost useless for pre-drivers in amps. Btw, Diodes Incorporated has its SMD versions, FZT558TA / FZT458TA. So, to be or not to be, the question is.Edit: Hmm, I didn't notice the transistor leads. They really look weird, like they have been attached by soldering. And btw, what 5X stands for ? Production year, month ? Nothing in the datasheets about those markings.

author: wraper
author_rank: Unknown
timestamp: November 04, 2022, 09:58:43 pm
content: Datasheet says hfe tested at 100mA. So if you switch it to 100mA, you should get proper measurement.

author: M4trix
author_rank: Frequent Contributor
timestamp: November 04, 2022, 11:04:01 pm
content: Unfortunately with this instrument you can't do that. But here are the values for the 2SA1486 (heatsink mounted) when in 10mA (Ib) position :Test voltage 5VIb - 7.3mAIc - 236mAhfe - 32 (instrument is showing 30)It looks like hfe (L category) is ok. Am I missing something or should I ditch the whole thing cuz expensive equipment is in stake.

author: wraper
author_rank: Unknown
timestamp: November 05, 2022, 12:04:02 pm
content: Oh, I thought 100 mA (Ic) was for hfe, but it's not. Maybe do some dynamic test with oscilloscope and compare with a known genuine part. Also try bending the leads of A1486 to front and back and see if they don't snap about 1.5mm away from the package. Or do something simpler like measuring CE capacitance and compare with a known genuine part.

author: M4trix
author_rank: Frequent Contributor
timestamp: November 05, 2022, 05:24:51 pm
content: Well, the problem is I don't have a genuine part to compare.The only solution left is to try them under real working conditions. I have a built rig for that. It's basically an 600W audio amplifier where I can easily attach/detach drivers and output transistors under test.Btw, B+D Enterprises is a reputable seller of obsolete parts. They are selling 2SC3840/2SA1486-AZ and the picture shows 2SA1486 with markings same as mine. I will send them a message and ask them the source of these transistors. I hope they will be honest with me.https://www.bdent.com/2sa1486-az-nec-switching-power-transistor.htmlCheers.