820 4924 taking 51 mA and not getting into S4 state

[Roan]

Sadly I dont have that much troubleshooting experience yet. Have rebuilt some backlight circuits and repaired the common iPhone errors so that's something.

The board Im working on now 820 4924 stopped working because of liquid damage and didn't turn on but with a light on the charger. Got the board out and it took around 36mA. Got the first few G3H lines as normal so went ahead to clean up the dirty corroded areas:
U3740
Q5480
Q1840
Q1842

I first was confused by the PPBUS_G3H being 12.5V for a macbook since I worked more on MBA's. Expected it to be 8.6V so looked around the ISL6259 and replaced it with a donor. PPBUS stayed the same and found out that the voltage is normal for the MBP's. Now it's starting around 44mA and working to 49-51mA after a few seconds. This after replacing the ISL and cleaning up. These are a few rails to get an idea:

PPBUS_G3H = 12.5
PPBUS_S5_HS_COMPUTING = 12.5
PP3V42_G3H = 3.42
PPBUS_S5_HS_OTHER5V = 12.5
PPBUS_S5_HS_OTHER3V3 = 12.5
PPVRTC_G3H = 3.32
PP3V3_SUS = 3.32


PP5V_S5 = 5.0
PP3V3_S5 = 3.32
PP3V3_SUS = 3.32

PP5V_S4 = 0
PPBUS_S4_X239 = 0

PPVIN_S0_CPUVR = 12.53

Looking around the web I expected that an S4_EN signal is maybe missing since I couldn't find any shorts on the S4 rails which might cause all S4 rails to be pulled to ground. Trailing back some S4_EN signals gets me to big BGA chips. When it is not reaching an S4 state, what would be some of the first useful enable signals to check? Or is there something that Im overlooking right now?

Thanks in advance!

 

[2informaticos]

First of all, welcome to the forum!

Be sure to use original 60/85W Magsafe 2 charger; forget about 1 -> 2 adapter!

Post PM_BATLOW_L, PM_DSW_PWRGD, PCH_DSWVRMEN, PM_RSMRST_L and PM_PWRBTN_L.
Trigger SMC_ONOFF_L and check for drop pulse at PM_PWRBTN_L.

Also try to start in SMC bypass mode.

 

[Roan]

Thanks alot!

The values I found are:
PM_BATLOW_L = 37mV
PM_DSW_PWRGD = 3.34V
PCH_DSWVRMEN = 2.5V
PM_RSMRST_L = 3.0V
PM_PWRBTN_L = 3.34V

When triggering SMC_ONOFF_L PM_PWRBTN_L goes to 0.36V

Looked up SMC bypass mode, suddenly it's alive! Does this mean that it looks fixable after all?

 

[2informaticos]

"PM_BATLOW_L = 37mV
----------------------
Be sure to use original 60/85W Magsafe 2 charger; forget about 1 -> 2 adapter!"
???

Check if starts with both charger and battery connected.

 

[Roan]

I've snipped this magsafe 2 which came in the box of an 2013 A1466. Now hooking it to a fully functioning an unsnipped 60W magsafe 2 and connecting the battery the device does not boot but has S0 rails. No chime no keyboard backlight or display backlight or display.

PP5V_S0 = 5.13V
PP3V3_S0 = 3.32V
PPVCC_S0_CPU = 1.85V
PP1V5_S0 = 1.5V

Cant find short so I think it's another simple thing I am overlooking. Fan is spinning but no questionmark folder.

 

[2informaticos]

"Fan is spinning"
In normal mode???
It should spin at max from the begining in SMC bypass; but fan only starts in normal mode when CPU gets really hot.
So, did you really start in normal mode?

 

[Roan]

It does not spin max, it only spins as if the CPU gets hot, so spins in normal mode and I did a start in normal mode.

I see that it probably spun because CPU got very hot. Trying it again now results in no fanspin at all. I do have Vcore. What is the thought process from here? Does the board need a battery to boot or is that a diagnostic trick? I remember reading old A1502's need a battery to start.

So far I'm thinking: ALL_SYS_PWRGD -> PPVCC_S0_CPU -> CHIME but not getting a chime

 

[2informaticos]

If you get VCORE, check PLT_RESET_L.
Also test for USB activity.

Try PRAM reset.

 

[Roan]

PLT_RESET_L = 3.32V
L4605 reads 5.13V when connecting a lightningcable with an iPhone, looks like this is normal

PRAM reset resulted in no chime no image flickering and no change as far as I can tell

 

[2informaticos]

I said test for USB "activity", no "power"; is a BIG difference.
Use a pendrive with Link LED; if flashes, activity is onfirmed...

 

[Roan]

The link LED flashes, so there is activity!

 

[2informaticos]

So no image, no backlight at this point?
Caps Lock reacts?

Test external video too.

 

[Roan]

No capslock react, sadly dont have another known good 2013-2015 Pro keyboard to test atm. No backlight, no image. When connected to an external monitor the monitor recognizes the power of the source but no further data (TV sees a hdmi being used but does not give image).

Since USB data does work, does this work towards corrupt BIOS or more CPU issues? Or does the Vcore already rule out most if not all CPU issues?

 

[2informaticos]

I'm not sure if you really have USB activity.
If you connect preinstalled OSX into pendrive, does it flash like loading OSX?

Try full known good BIOS...

 

[Roan]

oh sorry, the flashiing was only power, but since it connected poorly it flashed twice which I read as activity instead of power. Got a pendrive with link led which does not flash

 

[2informaticos]

So no USB activity, as I was expecting.
Now try BIOS.

 

[Roan]

Yep Im on it! One question, since I am just starting out I dont have a BIOS programmer I saw you recommending the Medusa programmer on the forum. The first version supports until 2017 models. Any benefit to going for the series 3 instead of the 2?

How do I go about flashing the SPI when I dont have a programmer? Desoldering and then :S? Or is the medusa mandatory for these BIOS modifications?

Thank you for helping by the way!

 

[2informaticos]

Medusa allows to read/write BIOS onboard and time is money!

You can do the job with any BIOS programmer and correct adapter.
This imply lot of time and not easy job.
Without Medusa, you need to do any mods on the BIOS file by software, in another PC.

 

[Roan]

Hi 2informaticos! I ordered the medusa and today it shipped right away. Meanwhile I was wondering if there are some videos on how to erase the current SPI ROM and how to write a full new BIOS to the chip. The manufacturer does not have many videos on that. Do you have any? I cannot seem to find any BIOS flashing videos of louis . Would like not to do it as trial and error since I heard plenty of horror stories about bricking a motherboard by installing the wrong BIOS or the right BIOS the wrong way.

 

[2informaticos]

Medusa comes with pdf manual.
You just need to connect it properly and move the switches according with the needed operation mode.