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Charger is green, then off, then green, no boot

Hi all.

I’m quite new at trying to troubleshoot logic boards, and have very little knowledge, but I’m trying to learn. So, I received a MBP 13” Early 2011. I don’t even know the conditions of the battery as it’s clearly drained and it won’t charge.

If I disconnect the battery, keep the power button pushed, connect charger, connect battery, release and push again the power button, the machine turns on, the display as well (white screen, no apple no nothing, chimes, fans spinning like crazy and that’s it. Reset SMC, machine dead again. Repeating the procedure and resetting PRAM after the chime also leads nowhere.

I removed the board. Upon connection of a magsafe (Apple original 85W), the light is green for some seconds, then goes off, then returns green and so on looping. Fans: same behaviour. When the green light appears, fans spin. Then they stop spinning (and the green llight goes off) and so on forever.

Following Louis Rossman’s videos and reading a few forums I started taking some measures, and here they are:

F6905 - 16.8V

U6900

  • Pin 1 - SMC_BC_ACOK_VCC - reads 3.48
  • Pin 4 - SYS_ONEWIRE - reads 2.91
  • Pin 5 - ADAPTER_SENSE - reads 2.90

U6901

  • Pin 1 - SMC_BC_ACOK - reads 2.36
  • Pin 2 - SMC_BC_ACOK - reads 2.36
  • Pin 4 - SMC_BC_ACOK_VCC - reads 3.48
  • Pin 5 - PP3V42_G3H - reads 3.48
  • C6908 - Pin 1 - PP3V42_G3H - reads 3.47

U7000

  • Pin 2 - CHGR_DCIN - reads 16.5
  • Pin 3 - CHGR_ACIN - reads 3.9

L7030’s reading goes up and down from 12.5 to 3.4, continuously

I then started taking some measures of a bunch of resistors and really got puzzled. I’ll explain why.

R7012 - 0.99 (should be 1)

R7010 - 28,3 (should be 30.1)

R7011 - 9.22 (should be 9.31)

R7013 - missing (should be 1)

R7015 - 100.2 (should be 100)

The issue here is the missing R7013. On the schematic there’s a row of 8 components (caps and res), but on the board… instead of said resistor I find two spots, and no trace of solder. It’s not the only case. R7002 seems to be missing as well, and R5011 too. It actually looks as if they were never there so I’m really puzzled. Here are a pic and a screen of the schematic.

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Any help is really appreciated.

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I wouldn't focus this deep on diagnostic process!

When you have resistors mounted you can't properly measure them this way! Let's not worry about these R7012, R7010, R7011, R7015.

Missing components is always tricky! R7013 is a no stuff. You can tell by the pads are bare. So that too is a red herring as well for R7002 & R5011. If you saw a pile of solder on the pads or burn marks then it might have been a component that failed or was pulled off, not the case here.

完成的

Thank you Dan. So where do I focus? And the L7030 giving me fluctuating readings instead of a steady 12V, what does that tell me? It seems that green light blinking at the same pace of the spinning/stopping fans and fluctiation of that inductor (I think it's an inductor, right?) are related. By the way, I have the same fluctuation in voltage when I measure F7040 as well

完成的

I was still writing my answer so I didn't see your update. Fluctuating values is a good clue! So how does this part of the logic board work? How does a voltage get created in the DC realm? Look over the schematics. Go back to your basic digial electronics.

Review the answer below first!

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So lets go through the diagnostic process:

Phase-1: What is the symptoms the customer is encountering. What happened to the system just before the failure and and additional background like liquid spills or alterations (RAM or Storage). Review the MagSafe charger being used is it a real Apple charger OEM MagSafe Chargers vs Cheap Imposters: Teardown for Truth & Real vs Fake Magsafe 2 Charger Macbook Pro is the cord and the connector in good shape? Apple Portables: Troubleshooting MagSafe adapters Also make sure its the correct wattage for the system. What is the color of the MagSafe LED a bright Amber or Green? Is the LED a dim Green?

If you have any question on the MagSafe try a known good unit {FYI: I have five different units just for testing). You could also get a good power supply and take a MagSafe power cord wired up for testing. But thats mostly useful after you’ve taken the board out.

Phase-2: Inspection & basic clean - Inspect the MagSafe connector on the system (DC-In board)are the pins clean and shiny?

Pop the bottom cover off, do you see any staining or wet areas, is there a lot of dust on the backside of the cover and the logic board. Use a 1” soft paint natural brush to scrub the surfaces to loosen the dust and dirt, use can’ed or compressed (oil-less) air to blow out the dust (don’t forget the fans) use care not to over power the fans (short blasts). Do you see any damaged components? Look for corrosion or off color solder joints.

If nothing is visible at this point fully remove the logic board to inspect the other side. Again, look for staining on the uppercase (liquid seepage) dust off the board, look for damaged components. Make note of areas impacted. Remount logic board and cables (not the battery). If needed replace the DC-Inboard before mounting logic board.

Phase-3: Power - With the battery disconnected connect the MagSafe charger. Did the system boot up? What is the color of the MagSafe (it should be Amber). Did the Fan startup?

So what did you find following this process? At this point you should have an idea where you need to focus in on.

Given the age of the system the battery will likely need replacing but without having a working system it’s not possible to test. You could create a power extension cable so you could leverage another working MacBook Pro as a test bed. This could be useful if you plan to work on a lot of this series.

From what you’ve described I would focus on the power logic. Focus on the MOSFET’s first, did you test them? Is the voltage on the power rails correct?

If they are correct then you know what the issue is don’t you ;-}

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Thank you for your help. Some info were included in the original post. I don't know the story of this machine. When I received it, I pushed the power button and all I got was a white screen without chime. The battery is empty, doesn't charge. Charger is an original apple 85W, the light is solid green but it stays on for some seconds, then it switches off, and after 1 or 2 seconds it gets solid green again, and it cycles so forever. I also tried a different original charger, also 85W.

I also tried to use a brand new DC-IN board, to no avail. The light never turns amber. All contacts are perfect, no sign of troubles there.

By removing the logic board I couldn't notice anything wrong (stained areas or signs of liquid) but I believe this board has seen other hands before, so someone could have cleaned it. Not sure.

完成的

The system doesn't boot, whether with nor without battery. Like I said in the original post, the behaviour is: green light appears, stays there for some seconds, then switches off, then reappears (solid, it's not dimmed), fans spin and after some seconds they turn off in obvious relation to the green light disappearing. When the green light reappears, fans start spinning again without pushing power button or anything.

I took some measures of U6900 and U6901, both belong to the MagSafe DC Power Jack on the schematic of board 820-2936-A. Values on the original post.

完成的

I also found clues on a different forum recommending the measure of U7000, pin 2 and 3 corresponding to CHGR_DCIN and CHGR_ACIN. Readings are 16.5 and 3.9, which seem correct to me.

完成的

Test the MOSFETs! Your look too far down stream of the problem.

Go back to the start of the power entering into the system. How does the system switch power from the DC-In Board to the logic board circuitry Vs charging the battery and how does the power from the battery go to the logic board circuity?

完成的

Yes, I tested the first components already, all those appearing in the MagSafe DC Power Jack scheme, page 63 of the schematic pdf. Page title: DC-In & Battery Connectors. I get the 16.5 V from the magsafe, fuse F6905 reads 16.8 which should be correct AFAIK, then there are two mosfets: U6900 and U6901. It's the first circuitry, including the 1-wire overvoltage protection. I posted all the readings in my first post. I am too inexperienced to understand whether all the readings are correct. I assume the 3 and 16 V are correct, I have doubts about those readings of 2.90 and 2.36. Dan, you keep asking me to test things I have already published readings of...

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