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[SOLVED]820-3787 Dead DC-IN Board + F7005 blown. Now quarter fan spinning

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phuketmymac

New member
Hi,

I have that board was not turning on at first + no green light.
Replaced DC-IN board as some diode mode very different from a known working one.
Still no go.
I saw a difference in diode mode on F7005 between each side of it. Replaced F7005. Got a quick green light on the charger then off, then green light again and off, etc...

Decided to use my DC power supply to power the board.
It tries to turn on, I am getting all the rails (it seems) for a second and then the amperage goes to 0.1 and back 1.5Amp. You can see the fans spinning and slowing down when the amperage goes down then back to normal speed.
It does that in loop like a quarter fan spin.

I've checked different the S0 rails and they all show a proper value.

I can't seem to find what's wrong with it.

History is : Mac was used with a knock-off charger.
Board looks fine under the microscope, no sign of corrosion or burnt components.

I am thinking, I should rework the ISL6259 area. What do you think?
 
bjf

bjf

Member
Any shorts to ground? Vcore, other lines? If no short, is vcore present during the cycle?
 
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phuketmymac

New member
No short that I could find at least.
Vcore is present at 1.8V when it turns on.

The weird thing is how quick it would turn off and back on again.

Now, not to forget this is happening with a DC power supply.
On a 85W magsafe, I get a quick green light and then off so there might be some short protection happening.

So far U7000, U7001 and U7100 have been replaced but no go.

I am assuming that I only have to check the S0 rails since Vcore is coming up but I might be wrong? right?
 
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phuketmymac

New member
Well I am not out of the woods yet.
Screen is now flickering. It seems to happen when the computer is switching graphics from Intel IRIS to Nvidia GPU.
Once connected to an external monitor, it is stabilized.

Could the Mux chip be dead in your opinion?
 
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phuketmymac

New member
Thanks for answering Duke.

Basically between switching from 1 GPU to another, the screen goes black (a fraction of a second)
A simple example is starting Final Cut Pro X which use only the discrete GPU. You'll see the screen going black very quickly and back to normal.

I'll post a video though in a few minutes.
 
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dukefawks

Administrator
Probably corroded trace to U5420. Maybe that will fix the flicker issue, but honestly I would not worry about a small flicker like that only when switching GPU.
 
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phuketmymac

New member
Well I did replace U5420 + check rework all the resistors R831X.
Funnily it did work for a while and once the customer came to pick up the laptop it happened again... some kind magnetism

Anyway, happy customer who didn't pay for the repair ;-)
 
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