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Dimmed green light on 820-2915

Yustina

Yustina

New member
Im new to this, been studying and researching hard to become familiar with what the components on the logic board do and I understand I have endless miles and years to go but, I will keep at this and keep learning because I absolutely love the field so, with no further ado, I have an 820-2915 that has a dimmed green light, I have an original magsafe (16.5 V) and get this reading down the line following the 1-wire circuit however, all goes to shit at the beginning, on U6901, dont get SMC BC ACOK, and no PP3V42_G3H, not knowing better and being extremely impatient I replaced U6901 along with U6900, when plugging back to charger I got a solid green light for about 20 secs then slowly dims to a barely seen green. I have been messing around with this board for a while now, all resistors seem to be reading as per the schematic, and when I get the solid green light I get all the appropriate readings on the various components but I am not fast enough to follow down the line before the light dims. There seems to be no signs of liquid whatsoever, this is my personal computer that out of the blue decided to not turn on any longer. Any ideas highly appreciated!
 
Alan.L

Alan.L

Member
Hi, first you need a 85w charger (18.5v) to troubleshoot all 15" macbooks pro. This is only charger you will ever need to fix any macbook boards.
 
Yustina

Yustina

New member
TCRScircuit said:
PP3v.42 voltage and diode mode readings to ground?
Click to expand...
Hhmm, on pin 5 of u6901 right? (Again, im new to this and my understanding is that PP3V42_G3H gets generated at pin 5 of U6901, of course I might be wrong. Im at work right now, will measure and post once I get back home).
thx for your help!
 
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dukefawks

Administrator
3V42 is needed and the first thing that needs fixed. Measure resistance to GND on L6995 and measure voltages on all pins of D6990.
 
Yustina

Yustina

New member
dukefawks said:
3V42 is needed and the first thing that needs fixed. Measure resistance to GND on L6995 and measure voltages on all pins of D6990.
Click to expand...

OK! the resistance to ground of the inductor L6995 measures .4-.5 Ohms, voltages of D6990 pin 1: .9mV , pin 2: 16.33 to 16.67V , pin 3: 16.43 V (I am using a 16.5V magsafe, my 18.5 is on the way!)

Thanx!

(I have taken off the inductor previously (L6995) and I still had that dimmed green light, so when placing it back on the board there was no change)
 
Yustina

Yustina

New member
Correct, I only get 16V. I am wonderig what could have caused the green light to be present for around 20 secs then slowly dimmed to a barely noticeable one and lost my readings.
 
Yustina

Yustina

New member
So, please correct me if im wrong, it is my understanding that 3.42V gets generated at U6901 so, if it is not being generetaed there and I have already replaced that chip a few times (with a known good chip), could it be that any component in the 3.42V line is preventing it from being generated at U6901?
 
Yustina

Yustina

New member
dukefawks said:
You get 16V on 3V42 rail?...I doubt it.

Measure voltage on L6995.
Click to expand...

No no, I get 16V on D6990 pins 2 and 3, Im sorry for the confusion, i thought we were still talking about the measurements from the previous post. Ill measure L6995 and will more than likely use a power supply at this point

thank you
 
D

dukefawks

Administrator
So 16V getting to U6990 which should be making 3V42 on L6995. Like mentioned before you claimed there was a low resistance to GND on L6995. So we can assume 3V42 rail is shorted to GND. Inject voltage on pin 2 of L6995 and see if anything heats up. Start with low voltage and don't go over 3V of course.
 
Yustina

Yustina

New member
ok, after a long work schedule I finally have one day off to mess around with this board, I checked my pp3v42 circuitry and EVERYTHING is checking out, with the exception of R8798, when testing in V DC I get minus 18mV and goes down slowly to minus 13mV, the resistance of this component is 00.4-00.2 when its supposed to be 0 and I am thinking its fine. I am still getting a solid strong green light that slowly becomes dimmed and barely visible. And I just noticed today that there is a buzzing sound coming from the board when its plugged in, it is slightly high pitched. No part of the board is getting hot to the touch. I see that R8798 is related to SMC_GFX_OVERTEMP_R_L and that is making me think there is a problem with the SMC, possibly GPU? I am going to keep researching on the schematic and explore different approaches, if anybody has any ideas please pitch in.
Thx in advance!
 
Yustina

Yustina

New member
I have replaced the SMC, reballed utilizing Jessa Jones pyramid method, surprisingly I still get all of my pp3v42 and again, same issue as stated, R8798 is measuring low, it is NOT on the minus any longer and goes up higher, around 23mV, but still same situation with the strength of the light on the charger, same buzzing. At this point either bad SMC chip (highly likely) or GPU. Of course, it is also highly likely that I am missing something since I have zero experience besides watching Louis R.and Jessa J. videos.
 
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dukefawks

Administrator
Did you use a known good SMC? Reballing it that way is not really suitable for an SMC and now has introduced another uncertainty factor. I also don't see what R8798 would have to do with the green light....
 
Yustina

Yustina

New member
dukefawks said:
Did you use a known good SMC? Reballing it that way is not really suitable for an SMC and now has introduced another uncertainty factor. I also don't see what R8798 would have to do with the green light....
Click to expand...

no, I dont know if the smc is good or not, it did not make a difference so , it seems im in the same boat.... Im here to learn so, I dont know if R8798 has anything to do with the green light, I was under the impression that pp3v42 is needed for the green light and I get all measurements except for the one at R8798.........
 
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