820-3476 no green light or ppbus_g3h

[ytesfay80]

I got a short to ground on pins 1 and 2 of R5530. Where should I go next in order to find the problem?

 

[aprendiz]

Apply 0.5V with power supply on that rail without limit current and feel what is getting hot, you can use the alcohol trick... If you don't see/feel anything go up on voltage little by little....

 

[dukefawks]

I can take a guess that U8080 is dead. You have 5V coming in and enable is high and the output is shorted. U8080 is probably getting hot too.
I assume you already removed the fried U7700!

 

[ytesfay80]

Wow I left the fried U7700 on the board the whole time and once I removed it the short was gone R5530 and when I plugged the charger in the fan spun and the cpu gets warm.

When I removed U7700 the pads for pins 9 and 10 were burned and came off.
Now I need to run a wire but I have never done this before. I have some very thin wire that was from a lvds cable. Can I just use a piece for each pad and put one side of the wire on the pad and solder the other side to the probe points that are next to it.

 

[dukefawks]

The CPU gets warm but does the board work? You should have an image without backlight now.

 

[ytesfay80]

I plugged the board into the computer as well as KB,TP, speakers but I don't get anything on the screen as well as no chime and no questionmark folder when i use a flashlight. When I checked PPVCC_S0_CPU i got somewhere around 1.74v and PP15V_TBT showed 15v.

I tried many scenarios to see if one of the cables might be causing this. I tried with & w/o the keyboard, trackpad, and display cable.
I used my thunderbolt to hdmi cable port, the hdmi cable in the hdmi port and that still didnt show and I also tried with the ssd plugged in.

Before this computer stopped working part of the screen would show lines going through and was messed up. I also believe the trackpad wasn't working but ill have to check with the owner about it.

I did all this with the battery unplugged because when I plug the battery in the charger just keeps flashing a green light and the fan never spins and nothing happens.

Also, I haven't put another chip on U7700 yet. I wanted to know where do I run the wire to for pins 9/10.

 

[aprendiz]

Use boardview and press "N" and write the name of pin 9 (ISNS_LCDBKLT_N), this will show you all the point where this "NET" goes, choose the closest one, in this case probe 541.... Same for pin 10....

 

[ytesfay80]

Okay I ran the wires to there points and put the chip on top. I get a short to ground in diode mode on both of the wires I ran but when I measure pins 3 and 4 of R7700 I get 15.75v so I don't know if the wires I ran are good.
Anyways I tried once again to turn the computer on and I still see nothing with a flashlight or with hdmi on tv. SMC_LID shows 3.37v so that isn't the issue.

 

[ytesfay80]

I checked all the power rails and they are all present except the thunderbolt rails are no longer there which is why thunderbolt to hdmi wasnt working.

I fixed the wires I ran on u7700 and they are no longer shorting to ground.
I've been trying to troubleshoot backlight on U7700 so hopefully I can see the screen is working. I am getting 15v on pin 3 and 4 of Q7700. The voltage dividers R7701/R7702 both measured the proper resistance and pin 11 of u7700 is not shorted to ground. I'm more familiar with the backlight circuit on the MBA than with these MBP retina's. Should I try replacing Q7700?

Any thoughts/ideas dukefawks larossmann aprendiz ?

 

[dukefawks]

IS the board even working? You are worrying about the backlight while there is no chime. Plug in an USB mouse and see if it lights up, of not the board is not even working....

 

[ytesfay80]

Yes. When I plug a usb stick in it lights up. I also get a fan spin and the cpu gets warm and ppvcc_s0_cpu measures 1.74v. All the main power rails are there except for thunderbolt.

 

[dukefawks]

Does a USB mouse light up was the question. Who knows what the light on the USB stick is for, it should probably blink if there is activity...
MOUSE!

 

[ytesfay80]

Okay yes I got a hold of a usb mouse and when I plugged it in it started flashing green lights.
When you test for that what does it tell you about a board?

 

[dukefawks]

I have no idea about lights on a mouse. A normal USB mouse has just one LED for the sensor, does that light up?

 

[ytesfay80]

yes. It started off flashing then the light stayed on.

 

[ytesfay80]

Should I start troubleshooting backlight even though i'm not getting a chime since the cpu gets hot and vcore is there?

 

[dukefawks]

First you need at least an image on the LCD. Got 5V on L8300?

 

[ytesfay80]

L8300 would fluctuate but the most I saw on it was 0.18v. I checked R8319 as well and it showed 0.1v and would also fluctuate. The resistance measured the proper 1k.

Also on Pin 1 of J8300(PPVOUT_S0_LCDBKLT) I get around 9v immediately after I plug the charger in and it quickly goes down towards 0v. I got 0v on LCD_PSR_EN, EDP_BKLT_EN, and EDP_PANEL_PWR.
Does that mean that the board is not seeing the screen. When the computer was working the right side of the screen was showing lines through it so that could be the issue.

 

[ytesfay80]

Is this an issue where the screen isn't being recognized?

 

[dukefawks]

You now first need to verify if the LCD is at least working. Try it on another machine of the same type. You can also connect an external LCD to the thunderbolt port.