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 Forum index » DIY Hardware and Software
Be very careful when ordering resistors from china !
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Sine



Joined: Sep 10, 2007
Posts: 111
Location: Netherlands

PostPosted: Thu Jan 29, 2009 1:35 pm    Post subject:  Be very careful when ordering resistors from china ! Reply with quote  Mark this post and the followings unread

A while back I was selecting 100k resistors for the summing stage of a VCO, the most common value in my belt was something like 100.6k

when I later wanted to select from that group the values where nowhere near what I had initially measured, even worse .. the longer I measured a resistor the lower its value got.
I first thought the multimeter was at fault, but another one gave me the same readings.

So then I suspected the resistors ( having seen fake transistors I wondered if they would mess with something as cheap as a resistor )
I took a few resistors and decided to do some temperature testing on them, I picked a "suspect" resistor, a carbon film
resistor desoldered from a board from the junk box, a resistor from farnell, one from Conrad, and another one from a local shop.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

I tied them to a power resistor together with a temperature probe and plotted the resistance versus the temperature.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Pink = carbon from junk box board
purple = farnell
blue = conrad
yellow = local supplier
brown = Chinese ebay resistor

X is in degrees celcius, Y is in kilo ohms
( that is 68 to 158 degrees Fahrenheit )

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The result is quite clear, I bought two sets of resistors from two different suppliers and both where ordinary 5% carbon film resistors marked as 1% metal film.

The fake ones are fairly easy to spot
1. Most if not all fake resistors I had had iron leads ( a magnet will help you out there )
2. The leads of these resistors are VERY flimsy
3. if you heat them ( soldering iron ) the resistance drops, in a metal film the resistance increases (slightly).

So be very careful where you buy, especially for synth applications the precision and the temperature coefficient really matter !
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Uncle Krunkus
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PostPosted: Thu Jan 29, 2009 4:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for pointing this out Sine. Smile

It also shows graphically the importance of not using any type of carbon film resistors in the V->I converter of a VCO, and for the effort it's worth, a VCF either.
This is something I'm sure I over looked when putting my ASM-2 together, and I'm inspired to check out exactly what resistors I've got in there now. Cool

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Luka



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PostPosted: Thu Jan 29, 2009 4:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

other than expo converters what applications is ~50ppm/K metal film really crucial?
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scriptstyle



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PostPosted: Thu Jan 29, 2009 8:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

i just received a lot of 1000 "1% metal films" off ebay. seller was sureelectronics. i wonder if these are really 5%. if i check these with a decent DMM and they stay at a stable level, this means that they are 1%? or close?
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gubbeper



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PostPosted: Fri Jan 30, 2009 12:17 am    Post subject: Reply with quote  Mark this post and the followings unread

As I mentioned elsewhere I just ordered a pack of resistors from Sure and I've now mailed them about this matter. I'll report any response here.
I actually encouraged them to respond in this thread Very Happy

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Sine



Joined: Sep 10, 2007
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PostPosted: Fri Jan 30, 2009 2:22 am    Post subject: Reply with quote  Mark this post and the followings unread

scriptstyle wrote:
if i check these with a decent DMM and they stay at a stable level, this means that they are 1%? or close?


The best way is to measure a common value ( say 100k ) and heat the resistor with a lighter or soldering iron.

If the value increases you have a metal film ( good ) however if the value drops you have a carbon film.
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scriptstyle



Joined: Jan 22, 2008
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PostPosted: Fri Jan 30, 2009 2:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Sine wrote:
scriptstyle wrote:
if i check these with a decent DMM and they stay at a stable level, this means that they are 1%? or close?


The best way is to measure a common value ( say 100k ) and heat the resistor with a lighter or soldering iron.

If the value increases you have a metal film ( good ) however if the value drops you have a carbon film.


ah thank you! im on the mission tonight.
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LektroiD



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PostPosted: Fri Jan 30, 2009 3:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Why on earth would people make fake resistors? It's hardly going to make them millions, in fact repainting them would turn into a loss, surely? Just seems a bit odd to me.

However, I'll test mine, and will be gutted as I have about 3 untested boards with them in, as well as a stripboard soundlab which is also untested, I think finding they are fake will put me off rebuilding these, or even building anything else (alongside a bunch of mandatory profanities).

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e-grad



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PostPosted: Fri Jan 30, 2009 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
Why on earth would people make fake resistors?

It's probably not faking but using a non-state of the art manufacturing process to save money.
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Sine



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PostPosted: Fri Jan 30, 2009 3:57 am    Post subject: Reply with quote  Mark this post and the followings unread

I don't know, selling carbon film resistors marked as metal film looks a lot like faking to me.

And they clearly are carbon. Look art the pink and brown lines in the graph, one is a known carbon, the other a chinese supposed to be metal film

Last edited by Sine on Fri Jan 30, 2009 12:22 pm; edited 2 times in total
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ericcoleridge



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PostPosted: Fri Jan 30, 2009 11:43 am    Post subject: Reply with quote  Mark this post and the followings unread

I've used these resistors on everything I've ever built!!! Just like the ones you've described. I've had many problems that could potentially be attributed to this, such as VCO tracking issues, etc...

What a drag.

On the other hand, they are dirt cheap, and most everything I've built works OK. But still...
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StephenGiles



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PostPosted: Fri Jan 30, 2009 12:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do these resisters find their way into Behringer products? Laughing
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mono-poly



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PostPosted: Fri Jan 30, 2009 12:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

No only Doepfer i guess.

Laughing
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JohnLRice



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PostPosted: Fri Jan 30, 2009 2:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thank you for the valuable and detailed information, Sine!
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bitmonkey



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PostPosted: Fri Jan 30, 2009 6:35 pm    Post subject: Re: Be very careful when ordering resistors from china ! Reply with quote  Mark this post and the followings unread

Sine wrote:

The result is quite clear, I bought two sets of resistors from two different suppliers and both where ordinary 5% carbon film resistors marked as 1% metal film.


I hear the fake ones contain melamine... Rolling Eyes

Nice job, Sine. Thanks!

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scriptstyle



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PostPosted: Fri Jan 30, 2009 8:34 pm    Post subject:   Reply with quote  Mark this post and the followings unread

seems like the ones from sure are fake Sad
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Sine



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PostPosted: Sat Jan 31, 2009 9:35 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, I heard that before, thanks for confirming.
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Tim Servo



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PostPosted: Sun Feb 01, 2009 11:07 pm    Post subject: Be very careful when ordering resistors from china ! Reply with quote  Mark this post and the followings unread

Wow, thanks for the info and careful analysis! It's amazing that someone would even bother, with something as cheap as a resistor, but I guess you always have to be a little careful. To tell you the truth, I don't even bother with 5% resistors anymore, and I only get 1% parts from Mouser or Futurlec. You can get them for about two cents each, and I've never had a problem. Thanks again for sharing the info.

Tim (cheap, and worth every penny) Servo
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Sound



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PostPosted: Mon Feb 09, 2009 6:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Sine, thanks for post it. Good to know it.
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Ypsi_Synth



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PostPosted: Mon Feb 09, 2009 9:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I bought from SURE and some other china ebay seller. All I can say is I WILL NEVER BUY FROM A CHINA SELLER AGAIN!!! I will stick with mouser or Allied Elec.

I have found that just about ALL goods made in China that do not have a US or Euro (or some rep. company) quality control have no quality at all.

I only use these crappy resistors in a pinch. Other than that.. support your local economy and buy known quality items.

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LetterBeacon



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PostPosted: Tue Feb 10, 2009 12:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

I bought a whole bunch of 100K potentiometers from Hong Kong a few months ago. Do you think they'll be of questionable quality too? Pots have quite a large tolerance anyway, don't they?
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Ypsi_Synth



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PostPosted: Tue Feb 10, 2009 3:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
I bought a whole bunch of 100K potentiometers from Hong Kong a few months ago. Do you think they'll be of questionable quality too? Pots have quite a large tolerance anyway, don't they?


Well.. look at it this way, even if there not great its not like you bought a KIA... you wont be out much, just learn a lesson like the rest of use.

PS(the Kia coment is my opinion. Donkt let it offend anyone Wink

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EdisonRex
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PostPosted: Tue Feb 10, 2009 4:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

I rented a KIA last summer for 5 weeks while we were back in the states. That's what you get for a minivan from Enterprise now. It was a good rental, but I don't think I'd buy one. So I see your point.

I use Alpha pots. So far so good.

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Ypsi_Synth



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PostPosted: Tue Feb 10, 2009 10:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

I love alpha pots!!!
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v-un-v
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PostPosted: Wed Feb 11, 2009 2:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Ahh China bashing time again eh?

Did you know that Alpha pots are made in Taiwan? I bet you if you guys were to look around enough in the USA, you too would find resistors made at a similar calibre to those crappo ones you bought in the land Chairman Mao? Remember China is a big place- hell, even my Mac and Dell laptops are made in China, so are most of my tools, and my Tektronix oscilloscope- and erm, my multimeter! Are you getting the picture?? Wink

We're entering one of the deepest recessions the world has seen in years. China and India (even, dare I say it, Iran and Iraq) are the very countries that we will need to turn to if we are to kick-start our manufacturing industries (not that we really had much 'industry' in the first place!- but that alas, is another story Very Happy ).

So the moral of this is;- Be very careful when ordering anything from anywhere folks, as cheap and cheerful usually means lame and shite- and that can be from anywhere in the world! Wink Very Happy
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