2016 A1706 Brain Dead.

Zebulon

Member
Hi everyone! First post here. I am hoping someone can help me with an issue I'm having with a 2016 A1706. I bought this computer from a guy who turned it on one morning and said he heard a little pop, then a little puff of smoke and a burning smell came out of it and it stopped working. I opened it up to find that a inductor had cracked in half, so I replaced it with the exact component from another board. It still doesn't boot up. I get 20v @ 2.76a. I have track pad click, the fans kick on after it gets hot and it will power USB device, but no image and no start up chime. With power disconnected it seems like most of the components above the CPU Near back of the MacBook are shorted to ground. Also voltages seem off from the schematics. At least in that area. I have attached an image with a circle around the component I have replace. Maybe the CPU is cooked?
 

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2informaticos

Administrator
Staff member
First of all, welcome to the forum!

I suppose you have 820-00239 board there.
Remember to post corresponding board code, when start new thread.

The circled coil is L7600, for 5V_S4.

"seems like most of the components above the CPU Near back of the MacBook are shorted to ground"
CPU coils have low resistance to ground as normal.

Post L7210 voltage after 15s.
Also check for USB activity (not power).
 

Zebulon

Member
Hi! Thanks for the reply. Sorry, yes it’s a 820-00239-A board. Not sure how to check for USB activity. When I plug a mouse in the beam lights up in the bottom, but what other ways might I check? I will post L7210 voltage after 15s. Tomorrow evening. Thanks again!
 

2informaticos

Administrator
Staff member
"Not sure how to check for USB activity"
Read here:
 

Zebulon

Member
Hi! ok, so Voltage on L7210 after 15s is 1.078 on pin 2 and 1.08.2 on pin 1. After plugging in a USB drive the light goes on and off a few times then stays on, just like when plugged into a working computer.
 

2informaticos

Administrator
Staff member
The board is stuck, doesn't boot.
CPU core should drop to 0.6V aprox, when board really boots.

Overvoltage occured on 5V_S4 rail and that might fried sensitive components.
 

2informaticos

Administrator
Staff member
There is no dedicated GPU; just Intel iGPU, embedded into CPU.

Very strange to get L7600 broken and nothing else failed on 5V_S4 power supply.
Do you get correct 5V at C7607?
 

Zebulon

Member
Thanks for the reply! The reason I was wondering if it’s the embedded GPUis because I found a video where the same MacBook has pretty much the same symptoms and the guy tests using an oscilloscope and shows that the board can’t complete the start up process and gets stuck similar to this board. I also find it strange that nothing else seems to be broken, yet it won’t boot. I will get back to you about getting 5V at C7607.
 

Zebulon

Member
Hi, sorry it's been a few days, but was super busy, now back to the fun stuff! :) ... Yes, in fact I get 5.16v at C7607.
 

2informaticos

Administrator
Staff member
Did you test the board alone on the desk?
No need to connect anything, apart of charger.
Just see if CPU core voltage drops from 1V to 0.6V after a while.
 

Zebulon

Member
Yes, I tested just the board on the desk. I will have to check the CPU core voltage again, but it was not going to 0.6v after a minute. It seemed to be staying at 1.08v.
 

2informaticos

Administrator
Staff member
You can use even CH341 if you remove the SPI chip.
However, Medusa programmer, with dedicated adapter, can do the job onboard.
You can find other programmers and adapters on Internet...
 

Zebulon

Member
I picked up a CH341A programer and was able to get a clean EFI BIOS written with my own serial numbers. It's back on the board and the voltage IS now going down after 10 -15 seconds, but it's going down to 0.544 volts and still no image. still 19.8v and 2.50a (after half hour or so it goes to 19.9v and around 1.77a) in the housing with everything, including the battery connected. After some time it gets very hot and the fans kick on. I'm stumped.
 
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Zebulon

Member
It does not appear to have any activity on a USB thumb drive with a light on it, nor does it show video on an external display.
 

2informaticos

Administrator
Staff member
Same behavior on all ports?
Check if you get 5V at L3500 and LB700; depending where USB device is connected.

Just in case, do PRAM and SMC reset.

And test external video with J8500 disconnected.
 
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