# Need help identifying these resistors!

Discussion in 'Electronics Resources' started by bobbyrae, May 14, 2009.

1. ### bobbyrae Thread Starter Active Member

May 14, 2009
42
1
I've been searching all over the internet, found lots of conflicting defintions, and so still feel a bit confused when it comes to identifying some of these resistors. I have heard some folks saying that 5-band just means more accuracy, less tolerance and the 5th band is tolerance, but others have said the 4th band is tolerance and the 5th is temp coefficient, still others say that the blue resistors are metal oxide, therefore automatically have a 1% tolerance and there is no band for tolerance; the 5th one is temp coefficient.

On top of all this, I can't even be sure which end to start on with some of these! The ones I am really frustrated with are R2, R4, R10, R12. And R12 - why is it GREEN? I heard someone suggest that might mean that it is actually an inductor!!!

Here it is:

http://xs.to/xs.php?h=xs839&d=09204&f=schbd_top817.jpg

Apr 5, 2008
19,173
3,836
3. ### bobbyrae Thread Starter Active Member

May 14, 2009
42
1
Bertus,

Thanks for the links, BUT ...

Which THEY are you talking about? Like I said, there many CONFLICTING definitions out there! Someone said that the blue ones are all 1% tolerance and do not have a tolerance band at all. Is that true?

Apr 5, 2008
19,173
3,836
Hello,

I can not see the picture anymore.
You can also directly upload the picture using the "manage attachments" button.

Greetings,
Bertus

5. ### DonQ Active Member

May 6, 2009
320
14
When the resistors get to 1%, you need a third significant digit, thus the extra band. Then a power of ten band. Then there can be, depending on other factors, either temperature or tolerance, or other things, sometimes even more than 5 bands.

They (the big they) say different things, because there are different answers, depending on a lot of variables. Fortunately, most of them pretty much follow just a few different standards. You just have to know how to read it... not just what color is what, but what combination of colors puts you into which standard.

For example:
You can also have a 5% or 10% resistor with 5 bands. For example: 2 digits, a power of ten, a tolerance, and a temperature band. You tell this from a 1% resistor by certain rings being certain colors that don't work for the 1% scheme, i.e. there is no power digit that is colored gold. This is the same way that you tell what end to start counting from on some of those where it is not clear. One way works, the other way doesn't.

Once you get past the 3 or 4 value bands, you generally have all of the information you need. After that, you almost to have done it enough (by looking through the references) to know by experience.

Fortunately, most of your components are marked on the board as R1, R2, etc. Another factor is that not all components that look like resistors are resistors (even some that are sometimes marked as resistors). At least some small inductors are also marked this way, and I've also seen pico-fuses and small axial capacitors that looked like resistors and were marked with colored bands. Any others?

6. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
104
Try this one.

2M2 1% or 214Ω 2%?

File size:
21.2 KB
Views:
267

Apr 5, 2008
19,173
3,836
8. ### DonQ Active Member

May 6, 2009
320
14
An example of exactly why I say things like "sometimes", "most of the time", "pretty much", "some of those", and so many more that I feel like I start to repeat myself.

This one gets into the area where you have to start considering that it might not even be a resistor, or maybe not a value from the standard available values.

I can not see the whole board, but it looks like the empty component below it might have been a trim-pot. Components around it look like it might be in the power-supply section. An ohm-meter check could tell if it was not a low value (e.g. if you read 3.9k, you would know that it was not 214Ω, but reading something low could just be some parallel path). All clues to the actual value.

As a last resort, one lead could be lifted and then read with a meter.

What is it really?

Apr 5, 2008
19,173
3,836
Hello,

It is 2M2 , 1 % , 50 PPM.

214 does not exist in the E-series.

Greetings,
Bertus

10. ### DonQ Active Member

May 6, 2009
320
14
That would have been my guess, but I would have done something to back it up first.

I also think that there is some sort of convention about thicker bands at one end or the other, but I've seldom seen this work since the bands are often not consistent widths. And sometimes it's hard to tell the difference between red and orange, especially if only one of these colors are on the particular resistor. If the resistor has gotten too hot, lots of other colors start to merge.This is a problem because a lot of resistors need to be replaced because they got too hot, and a multimeter may not help because many of them will have changed, or even be open-circuit.

At that point, it's an art.

And, oops!... I said that "there is no power digit that is colored gold" and did not use one of my "cover my a**" phrases like "generally" or "hardly ever". Your chart shows that there can be such a thing (I knew that once upon a time), but out of thousands of resistors in my part drawers, I only have two or three such things and I think they are from the stone age.

11. ### eblc1388 AAC Fanatic!

Nov 28, 2008
1,543
104
That's the point exactly. Why would user has to guess at the value if there is a simple way to remove the ambiguity all together. The manufacturers are to blame.

See the following image, it leaves no doubts as to what the value should be, i.e. 2M2.

File size:
21.2 KB
Views:
207
12. ### bobbyrae Thread Starter Active Member

May 14, 2009
42
1
Can you tell me what R4 is and how you came to that conclusion? R4's label is covered by a sticker, but it is a blue one right there in the middle between two light brown resistors. (BTW, I can see the whole pic fine at this point and there ARE scroll bars)

I think it is brown, orange, black, green, brown. And the brown is either tolerance or temp coeff. I read it that way because there seems to be SLIGHTLY more space between the green and top brown band than between any of the other bands.

That makes it 13M 1% or 100ppm.

13. ### Wendy Moderator

Mar 24, 2008
21,500
2,961
I would start from the end that is clustered, which reads red red black yellow brown (or gold).

220 (red red black) is a standard value.

I have to admit though, it's a tough call.

14. ### beenthere Retired Moderator

Apr 20, 2004
15,808
294
In this and similar cases, use a meter. If you know the resistance, then the additional bands make sense.