820-2850 no image, no chime

[sh33pz]

Hello,



I have an 820-2850 with no image and also doesn't chime.

Using 85w MagSafe official apple charger

If I take the memory out, it will beep and if I connect a mouse, it does light up.

I have tried another display as well to rule out a bad LCD.

No liquid, the board just stopped working.

The only odd thing that did happen was the unit did boot up once with an image and apple loading bar from my USB drive. I only had this happen once while I was swapping around parts turning it off and on.

Wondering if anyone has any ideas?

Thanks

 

[2informaticos]

Start changing C9560.
Do NOT use hot air; lift each pin with soldering iron.

Do you note VCORE dropping 0.2-0.3V few seconds after start?
Is better to confirm USB activity with OSX pendrive, with LED Link; if flashes OK.
Do PRAM reset several times; report if chime came back.
Do you get LCD_PWR_EN?
Disconnect LCD and test external video.

 

[sh33pz]

Before swapping out cap:

Do you note VCORE dropping 0.2-0.3V few seconds after start?
- yes, 1v then drops to .8v

Is better to confirm USB activity with OSX pen drive, with LED Link; if flashes OK.
- I have a USB stick with a LED on it that contains High Serria install, no flashing from it, tried both USB slots.

Do PRAM reset several times; report if chime came back.
- no change at all.

Do you get LCD_PWR_EN?
- no

Disconnect LCD and test external video.
- Can't test as I don't have the adapter to connect to thunderbolt.

While testing, I was able to get the unit to boot.


Basically, I left one of the fans off (one on the right side), the board was on for about 2 minutes while trying to boot stage as I had a phone call. While on the phone call, I hit the power button to turn off the unit and hit the power button to turn it on and well, it booted. The unit will never boot if I just connect the power cord, I have to turn it off via the power button and turn it back on. I also noticed, if I connect the other fan back, it will not boot anymore. So I turned off the unit to deal with it this morning and I was able to figure out a process to make it boot which is.

- Disconnect one fan
- Connect power cable so the unit powers on
- Let run like that for 2 minutes (the heat sink is pretty hot now)
- Press the power button to turn it off
- Press the power button to turn it on
Now it boots.

I know it's not healthy in letting it cook like that but it doesn't matter if the unit doesn't come back to life as it's not a customers device.

So I am assuming something on the board needs to get up to temp before it works which in turn tells me the board is trash possibly.


Anyhow, for giggles, I did swap the cap
- No change

VCORE was the same as well after the cap change, in fact, nothing changed at all with the unit.

Thoughts?

 

[2informaticos]

Droping VCORE is sign of boot.
But seems that your boartd gets stuck, maybe trying to initialize GPU.
When it boots,check in system report if GPU appears, or only Intel graphics is available.

Just in case, try one RAM module, each slot by separate.

 

[sh33pz]

It reports both GPU's the intel and the GT 330M, I am going to assume there is no fix other than disabling the NVIDIA GPU via some hardware mod?

 

[sh33pz]

Can HWMonitor be trusted? System total taking 47W, CPU VccSA 7A, GPU Die 236c insane numbers.

 

[2informaticos]

It will show correct GPU Die temp only if GPU is in use...
The other values are correct.