(347) 552-2258 [email protected]

U7000 is fluctuating

T

Tok Tok

New member
Hello,

I have this board that I've been working on for a while now. I've repaired a lot of issues but I can't figure out this last one. The voltage from the U7000 to the gate of the mosfets that are creating the 12.8v rail are fluctuating, the top one fluctuates around 10.51v and the bottom one 1.82v. The output is 8.42v to PPBUS_G3H, which should be 12.8v. I replaced the U7000 and the SMC but it didn't help. I also noticed that the pull up resistors between the U7000 and the SMC are fluctuating as well. The voltage drops from 3.5v to 3.4v and inbetween. Is this normal?

I've already checked the current sensing circuit but both are good.

Does anyone recognizes this problem or has any idea what could cause this?
 
larossmann

larossmann

Administrator
Staff member
What board is this? If this is a 17" then 8.4v is totally normal. If this is an old 17" then your problem is C7771.

Context is needed.

1) What machine is this?
2) What was the original problem?
 
T

Tok Tok

New member
Oh sorry I forgot to mention that. It's a 13" macbook pro 820-3115-B. I replaced the U9410, U3890, SMC, battery current sensing resistors and some other resistors and caps. The original problem was liquid damage. There was a ticking sound coming from the SMC, replaced it and now it is gone but I've had it come back once and it's gone again now.


Thinking out loud:

Which pin on the U7000 receives data to regulate the mosfets that create 12.8v? Or does this chip function on it's own and the SMC only tells it to turn on and off?
 
Last edited:
D

dukefawks

Administrator
Basic output voltage is set by pin 6. R7012 must be stuffed for 3S (12.3) output. After basic voltage is set it is regulated through SMBUS by SMC.
 
T

Tok Tok

New member
R7012 is good.

When I run the system of the battery everything is fine, I have all power rails and the fan spins but it does not chime and I have no enable signal on LCD_BKLT_EN and LCD_IG_PWR_EN.

Could this be a bad PCH? There is no sign of liquid damage in this area.
 
D

dukefawks

Administrator
Do you have an LCD connected else those 2 signals will of course do nothing. I usually connect a USB mouse, if the board works it should light up.
 
T

Tok Tok

New member
Yes I have, still no signal.

I haven't mentioned that the fan is spinning on high, even with all the components plugged in. So that means something else essential is missing. Can you tell me which components are causing a high fan spin when missing?
 
D

dukefawks

Administrator
Anything can cause that. If CPU Vcore is present and the board does not work it will be a shitty one. Corrosion under the PCH, or anywhere else for that matter.
 
JorgePayar

JorgePayar

Member
Tok Tok said:
Hello,

I have this board that I've been working on for a while now. I've repaired a lot of issues but I can't figure out this last one. The voltage from the U7000 to the gate of the mosfets that are creating the 12.8v rail are fluctuating, the top one fluctuates around 10.51v and the bottom one 1.82v. The output is 8.42v to PPBUS_G3H, which should be 12.8v. I replaced the U7000 and the SMC but it didn't help. I also noticed that the pull up resistors between the U7000 and the SMC are fluctuating as well. The voltage drops from 3.5v to 3.4v and inbetween. Is this normal?

I've already checked the current sensing circuit but both are good.

Does anyone recognizes this problem or has any idea what could cause this?
Click to expand...

I had the same issue on the same board, until I replace u6901 check for u6901 and u6900 and post values
 
T

Tok Tok

New member
Both have the expected voltages on all pins, 3.42v and 3.49v to be exact.

It does not chime, unfortunately.

I found a component that wasn't there, maybe I knocked it off myself. The U2652, which is a critical component. So I thought if I fixed this the board would work but unfortunately not. This does restore TBT_PWR_EN but it's not enough to make it work.

I'm missing a signal on AUD_IPHS_SWITCH_EN_PCH, which is SATA. This can be right, I have no HDD plugged in.

It still won't chime or give an image on the screen...
 
D

dukefawks

Administrator
This thing can have anything wrong, look harder for corroded or missing components. TBT,U9410,U3890 has nothing to do with basic power on. Also you did not answer if CPU Vcore is present.
 
larossmann

larossmann

Administrator
Staff member
psychic powers say corrosion under u1800, i would put kester 951 under and reflow. light reflow. not long.
 
larossmann

larossmann

Administrator
Staff member
the 951 is good because it evaporates away quickly and is clear like water so I can see the balls when they melt.

the nc-559-v2-tf is better for most use but it is tacky so i can't see shit when I do BGA rework with it.

I like to see when the balls melt and what it looks like with the camera.
 
larossmann

larossmann

Administrator
Staff member
also, the nc-559-v2-tf being tacky can cause misalignment of the chip if it starts bubbling because too much is there. you won't have that issue with the 951. so for large chip bga reflows, I suggest the 951. it's more beginner friendly.
 
You must log in or register to reply here.
Top