Buying cheap parts from ebay, what's the risk ? - Page 1
Forum section: electronics / projects

author: Refrigerator
author_rank: Super Contributor
timestamp: October 23, 2014, 07:56:08 pm
content: Hey guys.I've been thinking of expanding my little workshop and wanted to get some cheap parts to mess around on the breadboard and some projects. Been thinking of just going on ebay and ordering some parts since shipping is free, parts are cheap and i have a really low budget.But after i found some parts i liked i started wondering about them being genuine or not, since i don't really have anything to compare the price with.I only need some transistors and opamps.Transistors, well nobody fakes those but opamps, on the other hand, are another story.What i'm thinking of getting are these:http://www.ebay.com/itm/50PCS-LM358-LM358N-OPAMP-DUAL-0-70DEG-C-8-DIP-NEW-GOOD-QUALITY-/290739456963?pt=LH_DefaultDomain_0&hash=item43b16c0bc3I'm kinda new to the whole electronics market, would like to know if this is one of those "too good to be true" listings, although the seller has sold quite alot of them and seems to have really good feedback.Thanks in advance.

author: wraper
author_rank: Unknown
timestamp: October 23, 2014, 08:02:11 pm
content: Did you notice FT232RL tread? Well, they likely will work but may be out of spec and not TI at all.Quote from: Refrigerator on October 23, 2014, 07:56:08 pm

author: wraper
author_rank: Unknown
timestamp: October 23, 2014, 08:11:28 pm
content: I know that I received from this seller TB6560AHQ which were rebadged TA8435HQ. I would experience some firecrackers on the first power up if actually used them.

author: rastro
author_rank: Frequent Contributor
timestamp: October 23, 2014, 08:16:04 pm
content: I've gotten quite a few of my basic part needs met throughhttp://www.taydaelectronics.com/.I believe they have an eBay store but I order from their website. I'm not sure if they will ship to your location. I've used them for about 4 years with no complaints. They also run regular discount codes if you visit their facebook account.

author: daddario
author_rank: Regular Contributor
timestamp: October 23, 2014, 08:29:50 pm
content: Quote from: Refrigerator on October 23, 2014, 07:56:08 pmActually, counterfeit power transistors are a pretty massive business, which has been a subject of discussion in several usenet groups and forums for ages.Take all the countless "professional" PA amps with a myriad of different brand names, mostly packed with 2SC5200 and 2SA1943, proudly marked with "TOSHIBA" - yeah... naah. Unfortunately, the same story is often with spare parts on the market, unless you buy them from Farnell, Digi-Key, Mouser or some other credible distributor that's, well, how can I put it... "western enough".

author: Tandy
author_rank: Frequent Contributor
timestamp: October 23, 2014, 08:37:09 pm
content: I think it is fair to say that buying on eBay is highly variable, some will tell horror stories and others will tell you eBay is mostly ok and the horror stories are overblown.Where you buy your components from is all about what is important to you.If you are a hobbyist/maker who has plenty of time but very little money then buying a bag of components from eBay instead of having to pay high prices or deal with ridiculous minimum quantities from a big distributor is likely going to be fine as long as you accept some of the downsides. Unless your project is a demanding one component quality is not exactly top priority in most DIY projects. A majority of the components you get will work and because they are cheap you will sometimes get some that end up being duds. Buying from a Chinese supplier can also take a few weeks to arrive.If you are building something to sell then you need to be sure that components are genuine and comply with relevant regulations such as RoHS, if you are building on a small scale you can probably easily substitute components if your supply dries up.If you are lucky you will get genuine parts that someone has bought in bulk and is re-packaging into smaller quantities to sell you or selling excess stock .The three main things that go on are ...1. Re-cycled components, a great deal of electronic waste is sent to China for re-cycling and many of the salvageable components are removed and cleaned up to look new. There is little to no testing of these components so they may perform poorly or die prematurely as they are already used.2. Fake parts, functionally similar parts that may not perform as you expected as they are not the actual part you ordered.3. Rejects, components that have failed quality control tests but are still functional.That seller has a lot of feedback mostly positive so I guess that is a good start.

author: Refrigerator
author_rank: Super Contributor
timestamp: October 23, 2014, 08:45:40 pm
content: Now i'm mostly just fooling around the breadboard, but it would be nice if i could continue on my power supply project, opamps give me a nice and precise voltage regulation which i really like ( not without current boost transistors, of course ).Ps: i guess i could always just pump 20kV into those parts if they turn out to be fake ( one of those things i do for fun ).

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: October 23, 2014, 08:46:03 pm
content: Quote from: Refrigerator on October 23, 2014, 07:56:08 pm2N3055

author: Refrigerator
author_rank: Super Contributor
timestamp: October 23, 2014, 08:49:38 pm
content: Quote from: Alex Eisenhut on October 23, 2014, 08:46:03 pmWell, i had the TO-92 kind of transistors in mind.

author: wraper
author_rank: Unknown
timestamp: October 23, 2014, 09:50:29 pm
content: If they sell fake/recycled smt ceramic capacitors, why wouldn't they bother with transistors

author: grumpydoc
author_rank: Super Contributor
timestamp: October 23, 2014, 09:58:58 pm
content: The bottom line is that buying from ebay, especially from far east vendors. You might get OK stuff, you might not and it's hard to tell which sometimes.

author: ignator
author_rank: Regular Contributor
timestamp: October 23, 2014, 11:00:12 pm
content: If I wanted quality op-amps, I would not purchase TI PERIOD.Their copy of the National semiconductor LM124N did not meet spec. And caused serious production problems for me. It was interesting that our specification that dated from when the part was first available had clear instructions to not ever purchase TI parts. Purchasing had created some across the board purchase deal of TI, and ignored the warning.At any rate the product failed factory test. I had to create a new part number that called out the original part. So lot's of cost of creating specifications, and design changes to the existing drawings.

author: wraper
author_rank: Unknown
timestamp: October 23, 2014, 11:14:15 pm
content: Quote from: ignator on October 23, 2014, 11:00:12 pmGood luck purchasing National semiconductor parts as now they are part of TI. What a ridiculous requirements should have your schematic to use such a low end opamp and fail with it. Which specs particularly it didn't comply? IMO your design was fucked up or specified the inadequate part in the first place.

author: timb
author_rank: Super Contributor
timestamp: October 23, 2014, 11:49:39 pm
content: Yeah, TI make some of the best parts in the industry, Op Amps included. In fact, I'd rate Op Amps like this: Linear, Analog, TI.Sent from my Smartphone

author: dannyf
author_rank: Super Contributor
timestamp: October 24, 2014, 12:28:40 am
content: QuoteJust exactly what 'properties' your design relies so critically on?Sounds to me like a design problem than a part problem.

author: marshallh
author_rank: Unknown
timestamp: October 24, 2014, 12:34:56 am
content: I never buy parts from ebay. EverOnly exception is long-EOL'd parts that are completely unavailable elsewhere, and I vet/test the parts closely.

author: ignator
author_rank: Regular Contributor
timestamp: October 24, 2014, 12:50:04 am
content: Quote from: wraper onTodayat 07:14:15 PM>Good luck purchasing National semiconductor parts as now they are part of TI. What a ridiculous requirements should have your schematic to use such a low end opamp and fail with it. Which specs particularly it didn't comply? IMO your design was fucked up or specified the inadequate part in the first place.It was Vol, the output drove the base of an open collector switch (2n2222). 20mv is the guaranteed max. Typical parts from TI were 200-300mv, not even near correct (and put the transistor in linear mode). Design worked for 20 years without issue. When TI became contract purchased vendor, we had problems with many of their parts. The products were aerospace, Business and regional aircraft, jets and turbo props. Costs lots of money to support documentation changes. And as there were so many damn layers in the company with component engineering, purchasing, all of which had to find FAA approved process vendors. And the quality of the component engineers (application engineers is the newest title), these are the guys who couldn't get a job doing design work, as they can't read schematics, or know which end of the soldering iron to hold. Didn't use to be that way, previous generation knew the physics of the components they were cognizant of. When I pointed out the existing specification prohibiting TI as a vendor, the 'kid' said he'll revise that note out of the company spec.

author: timb
author_rank: Super Contributor
timestamp: October 24, 2014, 02:06:18 am
content: That doesn't make any sense.Sent from my Smartphone

author: aroby
author_rank: Regular Contributor
timestamp: October 24, 2014, 03:44:00 am
content: I'm just an (ad-hoc) hobbyist. I loaded up on common parts from eBay and probably spent $75 for 100s of pieces - I doubt I'll ever use most of them. Pretty much all of them have worked. A good few are out of tolerance, some by a wide margin, but if you're just playing around you can do some testing and find the parts that have the specs you need. The only failures I've had have been two LED drivers. The boards themselves were fine, but the voltage adjustment pots on both the original and the replacement were shorted. I had a pack of those pots from the same vendor an only half of them work (but at 10c piece, what do you expect?).If I'm building something serious (for me), I generally just order the parts I need from Mouser or Digikey.

author: Refrigerator
author_rank: Super Contributor
timestamp: October 24, 2014, 04:37:03 am
content: Those opamps do seem rather cheap, maybe i should order them and make a little test jig to see how they compare with each other ?

author: SeanB
author_rank: Super Contributor
timestamp: October 24, 2014, 04:51:20 am
content: Quote from: ignator on October 24, 2014, 12:50:04 amI see the issue, but did you have the 10k resistor to the negative rail as required to get them to pull down enough. The PNP pull down will never get to the negative rail without this.

author: StefanHamminga
author_rank: Contributor
timestamp: October 24, 2014, 08:24:43 am
content: I buy plenty of parts on eBay, which works pretty well so far. My strategy is to buy only easily diagnosable and replaceable parts.A 0603 resistor complies with the first, but not the second: If I have to diagnose and replace just one faulty resistor on a moderately dense PCB I lose more time/money than I gained by using eBay for any resistor ever bought there.Switches, batteries, motors, servos, etc are easily checked and replaced, so I buy those from eBay.The mentioned op-amps are a pain in the *** to diagnose and replace in a completed design.Maybe I should mention: All my designs are reflow soldered smd as much as possible and pretty densely populated (to save on PCB costs and for project demands), making replacement more difficult.

author: wraper
author_rank: Unknown
timestamp: October 24, 2014, 09:08:56 am
content: Quote from: ignator on October 24, 2014, 12:50:04 amSo which specifications it violated? If your design relies on undocumented feature specific to one particular manufacturer of the opamp, blame only yourself that you didn't use pull down resistor (conditions in the datasheet for 20mV).

author: dannyf
author_rank: Super Contributor
timestamp: October 24, 2014, 11:09:51 am
content: QuoteThat 20mv figure is given under certain conditions - the OPS is a complimentary emitter follower so the load must be very light. Your circuit has to satisfy that first for the 20mv to be valid.As to the TI figures, you are saying that either TI doesn't produce a product in spec (of its own datasheet), or its datasheet for that product is off.Neither is a credible scenario.

author: larsdenmark
author_rank: Regular Contributor
timestamp: October 24, 2014, 01:25:18 pm
content: Quote from: rastro on October 23, 2014, 08:16:04 pmI often use taydaelectronics. They have a lot of parts with very low prices. Tayda has the nicest packaging that I have ever seen. Shipping from Thailand to Denmark (Europe) is usually only 7 days with the cheapest shipping option (only 5 days for the last shipment!). In comparison free shipping from China/Hong Kong normally takes 3-4 weeks.I also shop on Ebay, but make it a rule that I check every shipment. When something is wrong then either the supplier or Ebay is helpful with refunding the money.

author: daddario
author_rank: Regular Contributor
timestamp: October 24, 2014, 11:31:15 pm
content: http://www.telemaster.ru/fuflo/Here's a nice a collection of counterfeit components.