820-02098 Stuck at 5v

[2informaticos]

If machine dean on update, DFU should recover it.
But missing 3V8_AON doesn't allow DFU.
Not sure what could happen there...

 

[prodigy83]

With both Q8500 and L8500 removed, I do get 3.8v on P3V8AON_SW1. I also get 12.2v on PPVIN_P3V8AON_ISNS.
So I very carefully put back on Q8500 and I am getting the 3.8v now on P3V8AON_VSW1, but as soon as I stick back on L5800, it brings the voltage down to 1.4v. Something on the side PP3V8AON_PH1 is bring everything down.

 

[2informaticos]

Just in case, change L/Q5800...

 

[prodigy83]

I have replaced L/Q5800, U5700, R5800, and I still am getting low voltage at L5800, it is still bringing the voltage down. I got 5.04v on the amp meter and it is pulling .42 amps.
P3V8AON_SW2 diode mode reading is .03, it should be .360.
What should I try next?

 

[2informaticos]

"P3V8AON_SW2 diode mode reading is .03, it should be .360"
Did you lift L5820, to see where the low value remains?

 

[prodigy83]

Yes, 1.44v on pin 2 of L5820.

 

[2informaticos]

I was talking about 0.03 reading...

 

[prodigy83]

"P3V8AON_SW2 diode mode reading is .03, it should be .360"
Did you lift L5820, to see where the low value remains?

Diode mode reading on pin 1 is .149
pin 2 is .030.

 

[2informaticos]

There is common point for all 3 coils.
Why did you fix on L5820 then?

You have something pulling down 3V8_AON rail.

 

[prodigy83]

Why did you fix on L5820 then?

Sorry? I don't understand what you mean by this?
I know 3V8_AON is the problem but I am not sure how to narrow this down to find what exactly problem is?

 

[2informaticos]

You've mentioned a problem with L5820.
But low diode mode reading is on its output pin; common with 3V8_AON power rail.
I don't know why you went for L5820.

There are many components connected, including PMICs and M1 CPU.
Is dificult to detect the culprit, once you don't have a pure short.
The problem may also be caused by some secondary power supply, derived from 3V8_AON.

 

[prodigy83]

I don't know why you went for L5820.

Oh okay, I went to that originally because when I removed all three L5820/40/00, the voltage went back up to 3.4v on pin 1 for all three. Where would you look to next then knowing this?
With L5800/20 both removed and L5840 back on, L5800 pin 1 is flucuating constantly from 4.7v to 5.7v.

 

[2informaticos]

Stop checking that point on a buck converter; there is no (pure) DC volatge!

Inject 3.5-4V into 3V8_AON and use thermal camera.
Give it some minutes and look for small temp diferences.
This may be waste of time...

 

[prodigy83]

Everytime I have done this, it comes back to U8100. UN400 could be an issue?

 

[2informaticos]

You can remove it and check if diode mode reading go high enough...

 

[prodigy83]

Removed U8100, PP3V8_AON is .054 diode mode. Did not go all that high.

 

[2informaticos]

The culprit is somewhere else...

 

[prodigy83]

Okay, let me bounce this off you then if I may. Since I removed U8100, the up and down voltage on L5800 pad 1 is now for the most part stable at 3.9v. This may be because of removing U8100? However in the process, I knocked a few other components around U8100 off. So I will be cleaning the area, reballing U8100, then sticking back all the components. I did however decide to take back up Q5800 (after having removed U8100) cause the solder did not look so great anymore. In doing so, I did see some of the solder under Q5800 looked somewhat grainy. I wonder if this may have been the issue? I keep going back to Q5800 because voltage in is at 12v, but voltage going to pins 6/7/8 are off. This appears to me to be an issue?
Your thoughts/knowledge?

 

[2informaticos]

Q5800's output voltage is controlled by U5700.
Keep in mind, there is no stable DC voltage; you get that after L5800.

When replace/resolder components, always apply leaded solder on the pads first.

 

[prodigy83]

Thank you. I have not put back U8100 yet but poking around P3V8AON_VSENSE diode mode reading is .05, should be .356. What is this sensing? I keep coming back to this area too but NOSTUFF is in this area.