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Pete, Computer Engineer
Category: Mac
Satisfied Customers: 17949
Experience:  Over 16 years of computer experience, CISCO certified
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Anyone familiar with Macbook Pro 13" logic board repair?, I

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Anyone familiar with Macbook Pro 13" logic board repair?, I am having trouble making sense of a reading, At Power IC TP51125, the vreg3 reads 3.3V which according to the schematic is good, and vreg5 reads 1.52V, according to the schematic it is supposed to read 5.5V. Now does this mean the the the TP51125 IC is bad, or is it another component dragging down the voltage?, thanks please help if you can I have a copy of the schematic
I am Pete, and I'll be happy to assist with your question today.

You should always have a 5.5V reading from the TP51125 regulator. Most likely the VReg5 device has failed and will need to be replaced.
Customer: replied 4 years ago.

Hi Pete, thank you, XXXXX XXXXX provide you with the schematic and board view file can you help me locate the VReg5 device connected to the TP51125 Power IC?, thank you, XXXXX XXXXX forward to hearing from you.

Hi Mike,
Yes I'll be happy to locate it for you.
You can attach the schematics here using the paperclip icon (fastest option) or email the file [email protected] with a link to this question.
Customer: replied 4 years ago.

Hi, Peter I emailed 2 emails the schematic and board view files to you, I put Attn:Customer thanks please if you can help me, I would be much gracious.

Customer: replied 4 years ago.

The board view files wont go because justanswer thinks they are viruses, is there any way I can get them to you?

Hi Mike,
If you can't email them, try uploading to a free file-sharing website, such as, then let me know the ID number to download them.
Customer: replied 4 years ago.

Ok, I will do that shortly, thank you

Ok, let me know when ready...
Customer: replied 4 years ago.

Hi, here is the rapidshare links:''Board%20View''%20file.brd


Hi Mike,
VREG5 is located on page 60 of the schematics (titled 5V_S3/3.3V_S5 POWER SUPPLY) -
it is coming from pin 17 of the U7200 QFN device.
Rather than a faulty device, it's also possible that the solder joint under pin 17 of this device is 'dry' - these can be difficult to rework as it is not possible to get more solder under the pin without first lifting the device.
Customer: replied 4 years ago.

what do you suggest?, should I lift device U7200, then apply flux and new solder?

Hi Mike,
You could try getting some solder in under the pin first - it may just even need reheated and reflowed.
If that does not work, then the device will need to be lifted and resoldered to the board.
Hi Mike,

I'm just following up with you to see how everything is going. Did reworking the U7200 device help?

Let me know,

Customer: replied 4 years ago.

No it didn't work, should I buy and replace the U7200 device?

The VREG5 5.5V signal is set by the logic inside the U7200 device, so it does seem likely that it will need to be replaced since you are getting a lower voltage output than expected.
Pete and 3 other Mac Specialists are ready to help you
Customer: replied 4 years ago.
I ordered the part, thanks, XXXXX XXXXX anyway to always request you?, you know your stuff, unopened up another thread, I need help reballing am Xbox 360
Yes, you can put "For ElectronicsPete" at the start of the question (or "ForCustomerquot; for computer questions - I am in both categories).
You should also be able to ask me questions from my profile page.
I will have a look at your Xbox question now.
Customer: replied 4 years ago.

Parts came in today, I am going to test them

Customer: replied 4 years ago.

Hi Pete, thanks alot!, I replacd the power ic, and the reg5 and reg3 readings are back up, but it still won't power on. I went to the transistor connector to reg5 Q7220, check it out in the board view file, aat pin #1 og Q722o, I get 0.05v as my reading instand of 3.3v, what do you think?, is something elses dragging it down or is that transistor faulty, at pin numbers 2,3,and 4 I get 12v readings, please give me your thoughts and what should be done next. thanks




Hi Mike,

Glad to hear that replacing the power IC partially solved the problem.
Troubleshooting at board level can be difficult, as soon as you replace one faulty part, you may discover another one, and so on!

A low voltage output from pin 1 of Q7220 could be caused by a faulty device, or it could be caused by a short between the two pads underneath the Q7220 device.
Check for any continuity between pins 2/3/4 of Q7220 and pin 1 of L7220 - there should be no connection. If there is, this indicates a short between the two pads under Q7220 (they are identified as pins 9 and 10 on the schematics).
Customer: replied 4 years ago.
Hi, thank you for responding your help is truly appreciated. How do I check for continuity for pins 2,3&4 ?, thanks please give me details on how to perform this test.

Hi Mike,
Pins 2,3,4 on the Q7220 device are all connected to each other, so you can choose any pin to carry out the test. These pins are also connected to one of the ground pads.
You will need to check if there is a short between these pins and pin 1 of L7220, which is connected to the other ground pad.
To do this, choose any pin (2,3 or 4) and use a continuity tester to check if there is a short to pin 1 of L7220.
If you don't have a continuity tester, you may be able to use the diode meter setting on a multimeter.
Customer: replied 4 years ago.
Do I perform this test with the MacBook logic board unconnected from a power source?, and also do I only use the red positive lead in this test, please illustrate for me how I use multimeter to perform this test

Yes, the board should be completely removed from any power source.
Let me know which multimeter you have so I can check if it is capable of carrying out this test?

I am going out now for a few hours so will catch up later...

Customer: replied 4 years ago.
I am using this multimeter:¤tURL=%253FNtt%253Dmultimeter&facetInfo=
Hi Mike,
I think your multimeter does have a built-in continuity test - see the white 'audio' symbol, just to the right of the 200 ohm mark?
Try using this setting - you will need to use both probes. When you touch the red and black probes together, you should hear an audible sound. This will confirm that the tester works.
Then hold one probe to pin 2 on Q7220 and touch the other probe on pin 1 on L7220.
It doesn't matter which probe goes where - you are just checking for continuity. If you hear a sound from the meter, then there is a short.

You can also test for a short by measuring the resistance between pin 2 on Q7220 and pin 1 on L7220 - use the lowest resistance setting (200 ohms). Again, it doesn't matter which probe goes where. If you get very high resistance, there is no short. If you get low resistance, this indicates that there is a short.
Customer: replied 4 years ago.
Hi, thank you

What would characterize a low resistance between pin 1 and pin 2, since I am setting my multimeter to 200 ohms
It's hard to say, as I don't have a similar board to test.
You should just get a high resistance error, showing that the circuit is open and all is good.
If you get any low resistance reading (200 ohms or below) then there is likely a short.
Customer: replied 4 years ago.
Ok I will test everything out
Customer: replied 4 years ago.

I testEd the component I got back no reading or responsI'm would this mean that the component is defective?, I get 1 which is the default number the meter starts with, do you think the fet is defective?

Hi Mike,
Yes, if you get a 1 then no short has been detected.
Therefore this indicates that the fault is with the device itself.
Customer: replied 4 years ago.
Ok thank you I will replace the device, to clarify if there were a short I would get a reading?, and what does a short mean?
A short means that there is an electrical connection. e.g. if solder was joining the two pads under the device, they would be 'shorted' or connected.
If there was a short/electrical connection then it would give a resistance reading.
Customer: replied 4 years ago.

I think I messed up the logic board even more, I accidently touched the board while it was plugged in. Now the TPS51125 power ic only gives me the reg3 (3.27 Volts) and reg5 gives me (4.99Volts) when I plug in the battery, it doesn't show any signs of life off of charger power. Please let me know which component may have failed, thanks