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820-4924-A Water damage, PPBUS_G3H fluctuate

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PatricF

New member
I have a Macbook Pro 13" Retina 2015 (A1502) with a 820-4924-A board. It got water damage and I got if for free from work to play around with.
I've watched many of Louises videos and I'm very interested to learn board repair as a hobby.

I get a green light (turns orange after a couple seconds) when connecting power. If I put my multimeter to VDC and measure PPBUS_G3H on F7140 it fluctuate from 3.2V to 11-12V with 5 seconds-isch between the highs and lows.

If I put it in diode mode (with no power to the board) and put the red probe on ground and black on F7140 I get 132 on the multimeter on both sides of the fuse.
I measured the same on F7700 and got 127 on both sides. I don't know if this is to any help since I don't have a know good value for this.

What can make it fluctuate like that? I've never heard Louise mention anything like that in the videos I've watched.
Or is it my multimeter? It's a cheap ass multimeter for like $15 that I borrowed from my step dad.
 
2informaticos

2informaticos

Administrator
Staff member
$10 should be good too.
Is not multimeter problem; you have a problem on the board.
Check if voltage on big coils fluctuate too.

Also try to start in SMC bypass mode.
 
P

PatricF

New member
No Title

JohnB8812 said:
Resistance between pins 17/18 and 27/28 of the ISL? Where was the original corrosion?
Click to expand...

Is the ISL the U7100 or U7200?
If I look in the schematics I only find these two with the name ISL that have up to 28 pins.
And by 17/18 and 27/28 do you mean resistance between 17 and 18 or 17 and 27?

My probes on my multimeter are two thick so can't seem to get an accurate reading. I tried to file them down but the only "accurate" reading I could get was from 17-27 on U7200 and it was somewhere around 10.6 Kohm

I'm gonna get some new probes tomorrow that will let me test this properly.

I've attached two pictures where the corrosion was. There might have been small drops outside the marked area.

2informaticos said:
$10 should be good too.
Is not multimeter problem; you have a problem on the board.
Check if voltage on big coils fluctuate too.

Also try to start in SMC bypass mode.
Click to expand...

By big coils do you mean the inductors?
I'm kind of new to this so sorry if I ask dumb questions.

I measured the voltage on L7130 and it fluctuate the same between 3.2-11V
L7520: 0-5V
L1295: 0-1V

I can't seem to find out how to start in SMC bypass though but I have done a SMC reset and that didn't do anything.

I just noticed that if I have the battery connected at the same time as the powe cable it stops fluctuating and PPBUS_G3H is 10.6V
I only tried this when putting it back in the chassi to try restting the SMC.

Does this narrow it down?
 

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2informaticos

2informaticos

Administrator
Staff member
Does it start with both charger and battery connected?
You only need board, charger and battery.
Just connect an USB mouse and see if gets light.

You can measure direct on the caps close to pins 17/18 and 27/28; ISL6259, of course.
Be sure there are good traces to ISL...

Press power button, connect charger and maintain pressing 5-10s (SMC bypass).

BTW, search for "fine multimeter probe".
 
P

PatricF

New member
2informaticos said:
Does it start with both charger and battery connected?
You only need board, charger and battery.
Just connect an USB mouse and see if gets light.

You can measure direct on the caps close to pins 17/18 and 27/28; ISL6259, of course.
Be sure there are good traces to ISL...

Press power button, connect charger and maintain pressing 5-10s (SMC bypass).

BTW, search for "fine multimeter probe".
Click to expand...

If I do this correctly I get 5.2 Kohms on 17/18 and on 27/28 I get 20 ohms
I measured 17/18 on C7150 and 27/28 on C7120 if that is correct.

I plugged in the mouse and it lights up both when power+battery is connected and also lights up when only power or only battery connected. When only battery was connected it took a couple of seconds for it to light up.

Also tried SMC bypass but it wouldn't boot.
I never get any fanspin.
 
2informaticos

2informaticos

Administrator
Staff member
"If I do this correctly I get 5.2 Kohms on 17/18"
There is your problem; you should get 3 ohms aprox!
Check R7051/52 ans their traces to R7050.

"I never get any fanspin."
Fan will start after looong time on this machine; CPU must get hot first.

BTW, do NOT quote an entire post from few cm above...
 
J

JohnB8812

New member
Ok so your issue is 17/18. One of a few things is true:
1. R7051 and/or R7052 are blown.
2. R7050 is blown (less likely)
3. The traces between R7051/2 and the ISL6259 are bad or the traces between R7051/2 and R7050 is blown
 
P

PatricF

New member
Ah thanks.
I can't find R7051 and R7052 in boardview though. I can find R7050 and that is exactly where the corrosion happened.
I'm at work at the moment but I will check this when I get home tonight.
 
2informaticos

2informaticos

Administrator
Staff member
"Check R7051/52 ans their traces to R7050.
----------
I can't find R7051 and R7052"
Sorry, I should write R7151/52...
 
P

PatricF

New member
R7152 2.4 ohm
R7152 5.8 Kohm

So I'm guessing R7152 is shorted to ground/faulty here?

When trying to measure R7152 I just touched C7150 and it broke of. So I will need to get replacements for at least R7152 and C7150

Is it possible to order these parts online somewhere like Mouser or do I have to get a donor board for these parts?
 
J

JohnB8812

New member
Just replace them from a donor board so much easier. Replace R7152 and C7150 and this should be fine would be my guess
 
2informaticos

2informaticos

Administrator
Staff member
C7150 is not critical...
You can test without it and should work.
However, is better to solder it, just in case.
 
P

PatricF

New member
Thanks. I just ordered a donor board.
Will replacing these components fix the fluctuating voltage when the battery is not connected?
 
P

PatricF

New member
Great. Thank you for all you help.
I guess I can try to put wires there if it will work. Is it magnet wire that I should use or could I use any copper wire for this since it only a replacement for a component?
 
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PatricF

New member
I bought a soldering iron and a hot air station to try and put wires in place of R7152. I ended up screwing up U7100 with the soldering iron and couldn't get the pins to connect to the board again and then I fucked up the pads on R7152 as well. The hot air station couldn't even get a resistor of the board so I guess it was a cheap piece of crap.

Thank you for all you help. To bad I suck at soldering so I couldn't fix it.
 
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