Fan stopps spinning when I'm trying to measure voltage.

[RioRio]

I have a 820-3476-A with fanspin but the CPU remains cool. When I try to measure ALL_SYS_PWRGD the fan instantly stopps spinning and the multimeter shows 0V.
When I disconnect the power cable and reconnect it, the fan spins again. But when I measure the resistors R8169, R8165 or R8168 at their pin 1 the fan always stops spinning. But not when I measure R8164, that one shows 3.3V at pin 1.

What could be the reason for the fan stopping when voltages are measured?

 

[2informaticos]

PM_SLP_S3_BUF_L is steady high?
If not, check U8180 voltages.
If yes, check R8167 value (ohm scale).

 

[RioRio]

PM_SLP_S3_BUF_L is constantly 3.35V, all U8180 voltages are 3.35V (except GND of course) and R8167 is exactly 10 K Ohm.

 

[2informaticos]

Post voltage on big coils of the board.

Check U1950 for corrosion.

 

[RioRio]

While waiting for your answer I have removed Q8150, to see if that's what's causing the problem. Then I measured ALL_SYS_PWRGD without Q8150 and the fan still stopped spinning. So I soldered Q8150 back. When I reconnected the board to do further measurements I noticed that the CPU got hot! I connected a display and I have a picture!!

 

[RioRio]

Unfortunately it is only partially fixed. Sometimes it recognizes the internal SSD, sometimes not. I noticed that when the SSD is not recognized, the SSD gets burning hot.

 

[2informaticos]

Try known good SSD...

 

[RioRio]

Same problem with a known good SSD. The big Samsung Chip close to the connector of the SSD gets very hot. On the screen there is a questionmark folder. In like 1 of 10 tries the SSD gets recognized and the OS boots, but it operates very slow.

 

[HeyWatchOutDude]

Turn on "verbose" mode so you can exactly see what is causing the slow OS boot.

1. Turn off mac.
2. Turn on mac and hold "CMD + V"
3. Boot Command Line should appear

 

[2informaticos]

"The big Samsung Chip close to the connector of the SSD gets very hot"
Do you mean the thunderbolt chip U2800?

 

[RioRio]

Turn on "verbose" mode so you can exactly see what is causing the slow OS boot.

1. Turn off mac.
2. Turn on mac and hold "CMD + V"
3. Boot Command Line should appear

Thank you, I will try this. It also runs slow after the OS booted up.

"The big Samsung Chip close to the connector of the SSD gets very hot"
Do you mean the thunderbolt chip U2800?

No, sorry that was misunderstandable. I mean the Big Samsung chip that is soldered on the original Samsung SSD. The same chip gets hot on a 100% known good SSD. While the same SSD does not get hot in a working macbook.

I have measured voltages on the pins of the SSD connector. I have only a working 2015 13" MBP for comparison. Most voltages are not identical but similar. The only big difference that I have measured is:
on the working board I have 0V on pin 50 and 3.35V on pin 52,
while on the faulty board I have 3,27V on pin 50 and 0V on pin 52.

On some pins that have only mV values there are more differences.

 

[2informaticos]

Is important to get correct signals on U3740 and its related pins on SSD connector.

What is the fault history for this board, any liquid sign?

 

[RioRio]

The board had traces of water damage at C8357. I have replaced it and have rebuilt contact to both sides of the board. Pad 2 of C8357 (which goes to the display connector on the other side) was gone. But now I have continuity where it is supposed to be.
Besides that, there were no other traces of water damage.

The values at U3740 without SSD are these:

1 - 3.41V
2 - 1.004V
3 - 3.29V
4 - 3.41V
5 - 0V
6 - 3.25V
7 - 3.30V
8 - 3.29V

With the SSD plugged in, these two values are different:

7 - 2.9mV
8 - 0.2 mV


PP3V3_S0SW_SSD is 3.35V

P3V3SSD_VMON is 1.004V

 

[2informaticos]

Voltages look good; with SSD inserted, of course.
Did you get these readings when the SSD is not recognized?

 

[RioRio]

I had these readings when the SSD was hot. I could connect a display to check if it gets recognized or not and repeat the readings. But I think the temperature already indicates that something is very wrong. It gets not only warm, it gets really burning hot.

 

[2informaticos]

Does this SSD work good in other machine?

 

[RioRio]

Yes. I am using it right now. And I have tested with another known good SSD which also gets burning hot on that particular board.

 

[2informaticos]

Check SSD connector, may have corrosion; replace if needed.

Change U3710/11, just in case.

 

[RioRio]

Okay, I will try. I've just made these two pictures with a thermal cam. It is the same SSD in both pictures. One in a working 13" 2015 MBP, the other one on that faulty 13" 2013 board.

 

[RioRio]

I have replaced U3710 and U3711. Unfotunately no improvement. The SSD connector looks good to me: