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How read apple schematic and take measurements

Hi everyone,

this is the first time that I m asking something on this forum and

I found a lot of useful things already but this time I have a question...

I m new with everything that comes about electronics and circuits and I m trying my best to learn in order to do some "small" board repair.

Recently I learned more about how to read a logic board schematics (along with a board viewer software), but what it's not that clear to me is that on the PDF are not shown all the values of voltage and current that all the pins are supposed to have...

My question is, how do you know if by taking measurement with a multmeter a pin (resistor or capacitor and so on..) has the right value or not?




I m using a software called Landrex Test link, downloaded from here

, would be nice to have a software that tells you all the properties of each pin


Hi guys! first of all thank you for you answer ..

I took some measurements and I could trace some power rails such as PPBUS_G3H and some more. Then, I decided to choose a random pin on the board view which is the R9720, Net: BKL_ISEN4 (logic board K29). The values for this pin using my multmeter are Ohm 0.07, V 0.01. Looking on the schematic I can not determine the right values that this resistor has to have, most probably I m looking in a wrong way but I will be more then happy if you guys teach me.

Is it the POWER ALIASES another way to call the POWER SYSTEM ARCHITECTURE?

I m using a dead logic board that I bought to practice with the multmeter

PS: John I m in this forum thanks to the youtube school ;)


Hi John,

On the motherboard it says w89190EB56GCA K24 2.26G BETTER and it s a 2009 apple macbook pro motherboard. My intention is not to definitely fix the motherboard, first because it’s old and second because I bought it online as a motherboard that has backlight problems and I don t have the rest of the computer. I want to learn how this board circuit work and how to reveal damaged chip/R/C/L/F, hopefully, without be annoying but enjoying with you in this useful forum.

In the meanwhile I bought a damaged macbook air that I should get in this days, in this way at the end if I ll be able to fix it I will be much more self motivated to keep doing that.

I m trying to attach a screenshot so you can see where this resistance is located in the circuits .. I m not sure if I did well.

Back to the question, how do I know what is the right ohm of this resistance R9720?


Answered! View the answer I have this problem too

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thats a hard question to answer, what board view software are you using?


What is the model number of the board. No the power system architecture shows you how the travel powers around the board and Power aliases are the different power rails at R9720 your looking for it's ohm measurement so you put both leads on opposite sides . Important ----Anytime you checking on both sides of the resistor with both leads testing unplug all power from machine including battery. When power is present in some form you need at least one lead on ground screw to not short the component or chip, it will arch on you too if your probes are to close to another component you need fine pin test leads and steady hands, regular probes can cause problems on board if your not skilled. Whats the problem of the board ?


The schematic will tell you do you see at bottom of R9720 on schematic ? there is a 0 or a 10 and the line squiggles? That is the measurement it should be in Ohms the % below means it can be in the in a tolerance of that higher or lower is ok within that. Measure R9717 through R9722 they should all be at 0ohms .


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Spread the Fixmas cheer.


Spread the Fixmas cheer.

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I don't understand exactly what your getting at? Open the board view open the schematic go to POWER ALIASES use nets to locate where ppbus_g3h is hanging on the board and with the other rails , and so on down the line. The schematic does give voltage, see whats off and track that area. This type of stuff can take a month to learn its best to do some youtube school :) for yourself. And just to let you know once you learn to how read a schematic it does'nt matter if its apple or not.

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PP5V, hmm, maybe 5 volts should be there.

47 ohms, hmm, maybe that should measure 47 ohms.


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The question is how to tell the voltage that pins are supposed to have. It says pp5v_s5 on a pin . that means 5 volts is supposed to be there. It says ppbus_g3h. that means 12.6v is supposed to be there. It says pp5v, 5v is supposed to be there.

It is listed on page three, a list of voltages and the numbers they are supposed to be. It says next to the resistor the number representing the resistance of the resistor. The question asks how you should know what is at the pins, and it is my answer that they are listed right there.

No one told me PP5V is supposed to be five volts. I had to figure it out by measuring and reading. I type here so you do not have to figure it out on your own. Posts like this inverter board for a1466? are step by step diagrams on not just how to repair complex problems, but how to troubleshoot and think through them.

I agree, I shouldn't be posting here. Figure it out on your own. Best of luck.


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patriziopanelli will be eternally grateful.
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