Hello guys,

I have been playing around with some pcb's and since my knowledge in electronics is very limited I had some questions. I hope someone can sheet some light on these for me.

Ok, I now have gotten somewhat comfortable when looking at a pcb so that I know what most of the IC's do. I noticed that the Maxtor and WD PCB's are pretty good at labeling components with a value or number. Unfortunately Seagate does not provide that luxury.

I could not hepl but notice the R, C, labeling on Maxtor and WD PCB's and I assume that
anything labled with an R = Resistor
anything labeled with an C = Capacitors
Can someone please confirm this for me?

Also when I measured what I believe to be the resistance with a mulimeter I received different values then expected. I measured R22 and I thought It should be 22Ohm, but it turned out to be somewhere around 650 Ohms. I measured this both on a fully functioning Caviar SE and on a faulty one. I must add that the multimeter that I was using is not state of the art , but I know it's functioning.

Ohh, also before I forget, what does the E label mean on the backside of the PCB?

Thanks allot!

Well, you are right about the labeling. It isn't a law, and it sometimes changes over the years, and by country, but in general:

R = Resistor
C = Capacitor
IC = Integrated Circuit
L = Coil
D = Diode

As for measuring in-circuit, other components can affect what you measure. If you learn Electronics in more depth, you will come across something called Ohm's Law. It's really a pretty simple equation, and it explains how a part in parallel with the measured part can affect your measured value. As always, if you need to check the exact value of a component, you need to remove it from the circuit, or if possible, lift one lead. Usually, you don't need to know the exact value. If a 220 Ohm resistor measures 218, it is probably within tolerances, and the circuit should work fine. If you measure less, like 100 Ohms, it's probably another part in parallel. If it's actually more, then it might be open, or defective.


I'm not sure why you're measuring 650 Ohms across a 22 Ohm resistor. One of the big rules about measuring a resistor with a multimeter is to measure it with the power off. If the drive isn't powered, it could be a charge left in a capacitor. Waiting, and/or shorting the resistor should let you measure it properly. It could also me your meter. If you touch the leads together, you should measure 0 Ohms.

Then again, if you think the resistor is 22 Ohms BECAUSE It's labeled R22, you'd be wrong. The parts are just numbered more or less sequentially.

Hello rchadwick,

Thanks for the quick reply!

Now that you mention it, I do recall being drilled in Ohm's Law some long, long time ago. I guess my mistake was that I assumed the label would include the value, but now that you mention it the sequential order makes sense. I was wondering about the odd values
I remember from long time ago, that the Resistors used to be color coded, but these resistors that I have seen locked a bit different. Do you know how to determine the supposed ohm value of the resistor without any color coding?

Thanks again!

get a metter, take the resistor out of the PCB, and messure its value.

regards
Pedro E.

Markings are limited due to the size of the surface mount parts. I've never seen color codes used on SMT parts. Some are completely unmarked. Most small value capacitors are unmarked. Resistors sometimes have numbers. A 472 would mean 4700 Ohms, or 4.7K (a 4, a 7, and 2 zeroes)

Pedro,
Thanks for your reply. I actually was trying to find a way to know the resistors ohm value and the compare it to the resistor real ohm value by measuring it.

Rchadwick,
Thanks for the reply. Yeah, I have not seen any color codes on the PCB either. I will watch out for the part numbers. But I guess the resistors probably don't go defective that often on the PCB's. It was mainly for my research and better understanding of the PCB. Thank you again for shedding some light on this.