Fake VOM1271 photocouplers - Page 1
Forum section: electronics / general

author: JackJones
author_rank: Regular Contributor
timestamp: November 16, 2018, 07:46:48 am
content: I got some VOM1271 photocouplers from aliexpress. Yes, I know, buyer beware when it comes to aliexpress, but this was from a seller I considered trustworthy. I've bought from them before, they've got 99+ rating. The price wasn't suspicious either, about €10 for 5pcs.As it turns out they were duds. First clue was that the physical dimensions don't match. The package was white, which isn't mentioned in the datasheet but all the photos I've seen have been black. And the package should be square, not rectangular like these traditionally are.Electrically they perform pretty oddly. The positive going waveform looks fine. But at turn off.. I have no idea what's going on there. I tested 3 separate chips, all look the same. I've attached a scope picture of the output, the light blue waveform is a TLP3906 from a reputable seller as a reference.Naturally I opened a dispute but aliexpress decided to give only partial refund. I've had some funny decisions from them lately. Like ordering a double sided A4 copper clad, receiving a single sided A6. Partial refund. Another incident was that a seller demanded I pay them extra after I placed an order and refusing to cancel it. I sent aliexpress three messages and their reply was to ask them nicely. The seller eventually shipped the order, with a fake tracking number. At least that time I did get my money back eventually.Just my small rant to start the day off nicely!

author: Mr. Scram
author_rank: Super Contributor
timestamp: November 16, 2018, 07:58:06 am
content: Can you use Paypal and reclaim the money that way?

author: JackJones
author_rank: Regular Contributor
timestamp: November 16, 2018, 08:01:55 am
content: I paid with a credit card, I don't think they even support paypal.The refund I got was about €7, so not sure if it's worth the hassle to do a chargeback with them for just €3.

author: amyk
author_rank: Super Contributor
timestamp: November 16, 2018, 01:03:35 pm
content: Quote from: JackJones on November 16, 2018, 07:46:48 amWhat picture did the seller have?One thing I like to do with possibly-suspicious sellers is to ask them to provide actual pictures of the product for closer inspection.A lot of them buy from someone else, and otherwise have little knowledge about what they're selling.

author: JackJones
author_rank: Regular Contributor
timestamp: November 16, 2018, 01:15:46 pm
content: Quote from: amyk on November 16, 2018, 01:03:35 pmI have never seen any other picture of this IC than the black square, and that is the picture the seller had too.Quote from: amyk on November 16, 2018, 01:03:35 pmIt was a dedicated electronics supplier, I have bought from them before and didn't really have a reason to be suspicious.One thing I noticed that it took them a week to post it from marking it shipped. Possible they didn't have it in stock after all and they just bought some from the cheapest supplier?Other thing is that this particular part doesn't seem to be available from any reputable seller, I don't know if it's been discontinued or what.

author: jaromir
author_rank: Unknown
timestamp: November 16, 2018, 01:54:12 pm
content: Quote from: JackJones on November 16, 2018, 01:15:46 pmNot sure if digikey is reputable enough, but they seem to have some on stockhttps://www.digikey.com/product-detail/en/vishay-semiconductor-opto-division/VOM1271T/VOM1271TCT-ND/3588699

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 16, 2018, 02:18:22 pm
content: Speculation of mine based on your waveforms and the following description. Italics are mine for emphasis."TheVOM1271Tis available in a small footprint andincludes an integrated active turn off circuit,to decrease MOSFET power dissipation."So what I think you got is a device whoseintegrated active turn off circuitis defective, sold on the Chinese gray market anyways, and then sold to you as a legit component.As you wisely mentioned, "Caveat Emptor" when dealing with AliExpress.

author: JackJones
author_rank: Regular Contributor
timestamp: November 16, 2018, 04:05:40 pm
content: Quote from: schmitt trigger on November 16, 2018, 02:18:22 pmI'm still curious about the package size. The datasheet lists it as 4.42 +/- 0.25, yet what I have is ~3.5mm. If it's a fake it's a pretty bad one. Then again, I've received MCP6002 opamps that weren't rail to rail so I guess you can expect anything.I'm not really bummed out about receiving fakes, mostly it's aliexpresse's response to this. Only a partial refund for an obvious case like this, I will really have to consider twice before trusting them anymore.Quote from: jaromir on November 16, 2018, 01:54:12 pmOops, didn't check digikey! But it does seem to be out of stock on many sellers.

author: jaromir
author_rank: Unknown
timestamp: November 16, 2018, 05:15:25 pm
content: Yes, for example mouser has empty stock with indicated lead time 57 weeks, similar with farnell. Unfortunately, this isn't uncommon in last one-two years. Components are simply disappearing for many months, just to reappear later. Often with increased price.So, buy the parts - as many you can consume in 2019 - at digikey while you can.

author: thm_w
author_rank: Super Contributor
timestamp: November 16, 2018, 10:34:31 pm
content: I see your photo on alix, the silkscreen clearly doesn't match other legit parts and doesn't match the drawing in the datasheet (no space between V and 503).There are other sellers with good reviews, so you might try your luck with them. I would probably trust a particular part from a particular seller, but not the seller themselves, due to the amount of dropshipping/etc involved, unless they are a part manufacturer.I'm also disappointed with disputes lately, not sure if its due to the number of disputes I have reached or a general rule for them to be tougher on arbitration. Its likely they are dealing with a lot of false/perceived false disputes, for customers to scam free parts. I always get asked to provide "video evidence", as they know this takes more effort than a photo.Also I had a seller be verbally abusive to me, and they did nothing, I suspect they don't even read the comments sometimes.