• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Non genuine components

Status
Not open for further replies.

dr pepper

Well-Known Member
Most Helpful Member
I just spent ages on a simple part of my project using an Lm358 op amp, its just a voltage follower, on a dc signal from 0v to +10v, to buffer & divide this signal by 2.
Couldnt get the bloomin thing to work, it would perform ok, then as soon as the i/p of one of the amps on the ic went below 1.2V the o/p would saturate at +vcc, had this before on a 741 op amp which isnt spec'd to go to ground on the o/p unlike the Lm358 which does go to ground, with this in mind I tried a '358 I had salvaged and it works perfect so it looks like these I have are fakes.
Maybe I should have known better for a quid for 20 of the,.
Anyone else had anything like this?
 

audioguru

Well-Known Member
Most Helpful Member
A TL071 and TL081 and the dual and quad versions have a problem called "Opamp Phase Inversion" where the output would suddenly go as high as it can when an input voltage became lower than the input common mode voltage range which is about 3V above its negative supply voltage that would be 0V in your circuit. Other opamps might have your 1.2V problem so yes your opamps are the wrong kind maybe marked wrongly as an LM358.
 

dr pepper

Well-Known Member
Most Helpful Member
Thats a pretty indepth site for Cf parts, I'll bookmark that one.

The marking on top is texas instruments, and theres the first suspicion, they came from a china seller, I havent had look with my microscope, might do that tomoz.
The markings look fine with a x3 lens.
And these Ic's are amplifiers, they do work but not as I'd expect, and not as the salvaged one I'm using, which is an St.
I suppose with my humble equipment and non expert knowledge I could be wrong, however I'd expect an amp designed to run from a single supply and have an o/p rated to go to ground, to actually do that, and not go nuts when you try to drive the o/p close to ground.
 

JonSea

Well-Known Member
Most Helpful Member
I made a piezo beeper replacement with a Linear Technology LTC6904 I2C-controlled square wave oscillator chip and an I2C digipot.

I built 10 of them and they worked as expected. I had 60 more built by a turnkey Chinese assembler. My test program should have generated a series of tones at different volumes but instead generated random beeps separated by periods of silence. Long story short - the LTC6904s were counterfeit and responded to aok commands on the I2C bus no matter what the address.

The counterfeit chips looked virtuly identical to the real thing I got from a known supplier. I don't blame my assembler for this problem; I believe they got cheated by their supplier.
 

tomizett

Active Member
A while back I had a power supply in which had a failed all-in-one flyback controller/switch, in a 3-pin TO220 package. Could have been from Power Integrations or someone similar... Anyway, we couldn't find it anywhere from the usual suppliers - only from one specialist who wanted about £15 GB for a single part. The other option was a tube of five for a fraction of the price from the far East, so we ordered some.
You've already guessed: none of the parts we received worked properly. Interestingly, they all failed in different ways - don't know if they where counterfeit, seconds, something else or what.
Long story short we forked out the £15 like we should have done in the first place and she was right as rain. Lesson learned.
 

schmitt trigger

Well-Known Member
Counterfeit devices are the scourge of the electronics industry.

If one has been working on it long enough, one must have been bitten at least once.

Depending on the quantities involved, it could cost a couple hundred millions of dollars. Google "Counterfeit Dell capacitor problem".
 

dr pepper

Well-Known Member
Most Helpful Member
This is a first for me noticing trouble with counterfeit electronic parts, however I repaired a piece of equipment last year, a plasma paper treater which involved fitting new bearings to a ceramic roller, well the ones I fitted didnt 'seem' right, and one cracked fitting it, they were £600 bearings, I'm glad I found out they were counterfeit before handing the machine back and wrecking an expensive piece of kit, and my supplier being reputable where gobsmacked and replaced them immediately.
Back in the days when there were electronic component shops here in the Uk, the owner of one was telling me he heard a tale that a rogue component seller supplied the M.o.d. with some T03 transistors rebadged as something else much more expensive, they all failed and the bloke in question never sold components again, messing with the inland revenue or the government isnt a good idea.

Edit: The Lm258's from Rs just arrived, these are On semi parts and hopefully are genuine, there are no signs as pointed out from the above article, and Rs are reputable.
 
Last edited:
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top