MBP A1502 820_3476A S0 Enable issues (total beginner)

[rodgsilva]

Hello, just a quick disclaimer... I'm a total beginner at logic board repair, just got my hot air station few weeks ago, so forgive if I'm missing something really obvious here.

I have a A1502 board here (820_3476A) that show green than orange light on the charger and fan spin, but no chime or image. (tried all the key combos resets)

No sign of liquid damage, only some minor corrosion on a couple of 201 resistors the I already replaced.

Seems like all the main power rails are present but there're issues with the S0 1.05v enables.

A1502_S0_Enable.PNG
I took the following measures:
P1V05S0_EN - 3.35V
P3V3S0_EN - 3.3V
P1V5S0_EN - 3.35V
P5VSO_EN - 3.35V

I'm don't know what could cause the higher voltages on the 1v lines.

The other area that I believe could be related and also have some weird values is the U7600
A1502_S0_U7600.PNG

Here's some readings:
IN
Pin - Name - voltage read
12 - V5IN - 5.16v
2 - PP1V05_S0 - 1.04V
17 - P1V05_S3 - 0V
16 - P1V05_S0 - 3.35V
6 - VREF - 1.8V
8 - REFIN -1.05V
19 - MODE - 0V
18 - TRIP - 0.16V

OUT
15 - VBST - 6.16V
14 - DRVH - 1.36V
13 - SW - 1.05V
11 - DRVL - 3.5V
20 - PGOOD - 3.35V
9 - VFFQSNS - 1.05V
5 - VTTREF - 0.52V

Well, that's all the data I gather so far, unfortunately I don't have a known good board or even donors to take as reference, also don't have a power supply yet so I can't tell how much current is taking.

I would appreciate any input for what I could look or try to replace.

This is just a fun learning experiment for me so no pressure if I make worse but I would be very glad if I could fix.

[reformatt]

So you have fan spin? Check voltages on L7630 and L7310. Be extremely careful probing around the +1.05V converter while it's on as that's a great way to kill a PCH. Logic levels for enables are supposed to be 3.3V BTW.

If you are getting Vcore, then it's something beyond G3 to S0 state.

[guruji]

checlk load switches they are tiny 8pin ball chip like glass top they are the cause.3.3_s5 to 3.3_s0 5v_s5 to S0 and so on for other voltages.

[rodgsilva]

Originally Posted by reformatt

So you have fan spin? Check voltages on L7630 and L7310. Be extremely careful probing around the +1.05V converter while it's on as that's a great way to kill a PCH. Logic levels for enables are supposed to be 3.3V BTW.

If you are getting Vcore, then it's something beyond G3 to S0 state.

Hi thanks for the input.
Yes I do have fan spin and Vcore voltages.
L7630 = 1.05v
L7310 = 1.7v

So if the enables are correct than I'm not sure what I could check next...

Originally Posted by guruji

checlk load switches they are tiny 8pin ball chip like glass top they are the cause.3.3_s5 to 3.3_s0 5v_s5 to S0 and so on for other voltages.

The only "glass like 8 pin ball chip" I could find was u2940
And I have the following...
Pins 1 2 3 4 5 and 6 = 0.9v
Pin 8 = 3.3v

[reformatt]

He's referring to the switches on Pg60 of the schematic. Like U8030 for example (3.3V S0 switch). Often with these boards its some kind of shorted cap on switched power rail.

I normally go through the output of each one and check resistance to ground (with power off of course). If you have fan spin, then it's easy to check the output of each one for voltage.

A very close examination of the board under a microscope usually presents some kind of corrosion somewhere. It can be quite minor too. Had an insect die on top of a cap once on one of these boards, and the cap went short as a result.

[rodgsilva]

Originally Posted by reformatt

He's referring to the switches on Pg60 of the schematic. Like U8030 for example (3.3V S0 switch). Often with these boards its some kind of shorted cap on switched power rail.

I normally go through the output of each one and check resistance to ground (with power off of course). If you have fan spin, then it's easy to check the output of each one for voltage.

A very close examination of the board under a microscope usually presents some kind of corrosion somewhere. It can be quite minor too. Had an insect die on top of a cap once on one of these boards, and the cap went short as a result.

Ah got it, thanks for the clarification.
I just checked the switches and they seem to be fine.

I was able to get a working board of the exact same model so now It makes a lot easier since I take references. With that said I guess I found at least part of the problem...

SPI U6100 (Bios)
On the good board I have:
Pin 2 - SPI_MLB_MISO = activity from 0 to 3.3v
Pin 5 - SPI_MLB_CLK = from 0 to 20v (maybe 0.40v)
Pin 6 - SPI_MLB_MOSI = from 0 to 20v (maybe 0.40v)

Dead board:
Pin 2 - SPI_MLB_MISO = Static 3.3v
Pin 5 - SPI_MLB_CLK = 0v
Pin 6 - SPI_MLB_MOSI = 0v

All the other pins are fixed at 3.3v on both boards.
No shorts and the resistors around the area seem the match values with the good board.

I guess this narrow down to bad SPI chip or PCH right?

There's any other thing I could do to try isolate the culprit?
In any case reprograming the BIOS chip or BGA work for the CPU is way beyond my league at the moment.

So after all the correct term would be "brain dead board", since I've learned that all the Enables were just fine

[reformatt]

For a bad PCH, check resistance to ground on L7630. The value will vary downwards when the CPU is hot, so check it at room temperature. About 150 ohms or so on some boards I have here. Anything under 50 ohms here would be suspect.

First thing to try would be a donor BIOS. You can transfer U6100 from the other board to test, bear in mind the boot process will be slower due to a dirty ME. But it's useful to at least see if the board boots. I also use a USB-C power meter connected to 85W brick charger, and a USB-C to Magsafe 2 adaptor to check current. This can reveal a lot of what a board is doing once you have a bit more experience.

Check the Repair wiki for this board for some pointers. You can also use this to troubleshoot beyond S0 state

https://logi.wiki/index.php/Bootup_Signal_Order

Again, look really closely at the board for corrosion. Macbook boards have plenty of unprotected copper test points, any that are discoloured can often be found to be open circuit when you scratch at them.

[rodgsilva]

I'll check the resistance later today and report back.
I got confess I'm a little afraid with the idea of removing the BIOS from the good board and end up with two bricked A1502 haha So I guess I'll try to find another donor first.

I already got the USB-C power meter to deal with newer models but I did not know i could use with an adapter to check current on the magsafe, I'll try to find thanks for the info.

I don't have a proper microscope but my setup its pretty good for close inspection, with a Sony A7 camera combined with macro lens and a HDMI out to a 20" monitor.

So the board its pretty good looking overall it was just "dusty", however I did find a ugly looking 201 resistor next to the Bios and I replaced already, so this could also indicate that the SPI chip got corrupted or just dead I guess.

[rodgsilva]

Originally Posted by reformatt

For a bad PCH, check resistance to ground on L7630. The value will vary downwards when the CPU is hot, so check it at room temperature. About 150 ohms or so on some boards I have here. Anything under 50 ohms here would be suspect.

Just checked and I have 153ohms from L7630to ground, so pretty close to your reference.