First Board Repair 820-2936 - quater fan spin.

[DataQueue]

Hi all,

This is my first board repair, I am not a professional and just a hobbyist. Possibly some typos as I am going off my written notes from a week ago.

History:
Corona free macbook.
I was gifted the machine. It had a bullet hole through the screen and was crusty with dirt and pubes on the inside. Cleaned up nicely, no obvious corrosion. I spend an hour examining under the magnifying glass before I cleaned it up, after testing.

I have the screen if anyone wants to see a pic of the hole (bullet hole to be clear).

Board symptom:
Quater fan spin, no vcore. some voltages pulsing with the fan (see further down)

What I have done:
I replaced C1724 +1723 and R7005. I measured the resistor incorrectly, but I did a passable replacement job, not completely new to soldering and heat gun work. Essentially replaced as I am a moron.

Measurements:
PPBUS_S5_HS_Computing - 12.6v (good?)
CPU Vcore - dead, no pulsing with the fan.
All_sys_PWRGD - Pulses with fan spin.
PPVCORE_S0_CPU - Dead
PPVCORE_SO_AXG - Dead
PP1V2-S3_ENET_INTR - Pulses with fan.
PP1V05_S0 - Pulses with Fan
PP3V42_G3H - 3.48V
PPBUSG3H - 12.6V
PP3V3_S5 - 3.32V
PPVCCSA_S0_CPU - Dead
PP1V8_S0 - Pulses on fan spin
PP5VS3 - Pulses on fan spin

I Probably over measured, but I wanted the practice on the book of mac.

Assumption (probably wrong - noob):
Thinking I need to concentrate on U2800 or U7400 any ideas how I test these better?
U7000 I see 3.1 ohms between 17 & 18 i did see elsewhere that it probably should be 2.2ish.



Need tips on where I go next, please. I really am a noob at this.

Thanks
DQ from Australia.

 

[2informaticos]

First of all, welcome to the forum!

Do not bother more with U7000, as you have correct PPBUS_G3H voltage.

"PPVCCSA_S0_CPU - Dead "
This is a problem, if you don't get pulse at least, like in other points.
It is required before VCORE appears.
Check diode mode to ground at L7100 and some voltages at U7100; pins 7, 15, 19, 20.
Try to catch any pulse, if possible...

 

[DataQueue]

Hi, you were right @2informaticos . My initial measure of PPVCCSA_S0_CPU was a regular spike with the fan, with my crappy multimeter was reading a 1.5vish spike with the fan.

Diode mode to ground on L7100 gives me 0.016

Caveat; I need better optics, I have a magnifying glass with a light, but I have something better on the way. Nothing like what the pros use though, but it should give me better vision.
U7100
Pin 7 - VCCSAS0_SREF - pulses to about 1.5 . again a slow multi.
Pin 15 - PVCCSA_EN - Looks like it pulses to about 3.8
Pin 19 - PP5V_S0_VCCSAS0_VCC - Pulses 80-100mv and over and then slowly (ish) drops back to 0 before the next pulse, again.
Pin 20 - PP5VS0 - Pulses with the fan and drains. Again seeing about 90mv on average.

And thanks..

 

[2informaticos]

Surelly no pulse at all at VCORE?
Check R7402 ohm value.

 

[DataQueue]

r7402 is 90.8k ohm, checked it 3 times to be sure. Vcore is not pulsing, at least at the few multiple points I have tested at.

Vcore at c1682, c1680 and c1683 no pulse at all. I also checked r7510 pin 1 for good measure (not necessarily in that order).
Note: I'll have to learn how to read (and understand) the board docco PDF better.

 

[DataQueue]

This is the screen, a trophy in my work space.

 

[2informaticos]

Test the board aione on the desk; nothing connected, apart of Magsafe and fan.
Check fot pulse at coils; pages 67, 70/71.
Also check for pulse all the power rails at pages 71/72.
Check for short, where no pulse detected.

Did you try to start in SMC bypass mode?

Inspect all SPI Bus Series Termination resistors and their traces.
Try known good BIOS too...

 

[DataQueue]

Hi,

Yeah it was already out. I'll do all of this tonight.

I'll have to google the SMC bypass mode etc whilst I am at it. I am new to Macbooks.

Thanks again. for all your help.

 

[DataQueue]

Hi , not finished yet, just keeping a log.

If I am reading right the output voltages from page 71
PP1v8_S0 - pulses
PP1V2_S3_ENET_INTREG - pulses
PP1V05_SUS - a nice and good 1.06v steady
PP1V05_S0_PCH_VCCSADPLL - pulses
PP1V5_S0 - Pulses

From Page 72
PP3V3_S4 - solid 3.33v
PP3V3_S3 - pulses
PP1V5_S3RS0 - pulses
PP3V3_S0 - a bit sus, it wiggles and pulses a bit but not high. I either can't get a reading on it at multiple points... OR..... something is wrong. not pulsing very high at all (90mv), and showing Open Line briefly.
I went to q7830/c7830 same result. I am getting 10k at c7830 for PP3V3_S0
PP3V3_SUS - 3.3v
PP5V_SUS - 5.00v

At this point going to call it a night as it's late. Will pick it up tomorrow and continue. Am I onto something with PP3V3_S0? Feel like such a noob with this stuff.