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820-00281 No image

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tcampbell34

Member
Hello. I have a 820-00281 that took a heavy blow to the keyboard by some kind of heavy object. There is significant indent in the keyboard around the U, I, J, and K keys and the whole keyboard itself is not functional anymore. I put the board in a new topcase and it turns on, keyboard works, and the board seems to boot but I have no image on internal or external display. Caps lock key works when pressed, USB drive with OSX lights up and flashes when connected, and after about a minute or so, the touchbar turns on. I checked the voltages for the LCD, with the LCD connected ,and have listed them below. EDP_PANEL_PWR_EN and PANEL_FET_EN_DLY are fluctuating between 0-0.5v so thinking maybe there is an issue with U9800? The board is spotless and has no signs of corrosion or other damage that I can see.

PP5V_S0SW_LCD - 0v
PP3V3_S0SW_LCD - 0v
EDP_PANEL_PWR_EN - Fluctuates between 0 and .5v
PANEL_FET_EN_DLY - Fluctuates between 0 and .5v
DFR_DISP_PWR_EN - 3.4v
BUF_EDP_PANEL_PWR_EN - 0v
BUF_SMC_REST_L - 3.4v
DFR_DISP_SMC_RST_L - 3.4v
SMC_RESET_L - 3.4v
DP_INT_HPD - 0v
 
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tcampbell34

Member
Yes I do have voltage on all the GPU coils. The indent in the keyboard is very close to where U9800 is on the board so its definitely possible there is a broken trace or solder under it.
 
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tcampbell34

Member
I pulled U9800 and checked continuity between some of the pads and the resistors around it and did not find any broken trace. I replaced U9800 from a donor, but still have the same issue. EDP_PANEL_PWR_EN still pulses from 0-0.5v. Do you know what would cause that to pulse?
 
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captainmac

Member
i have one that has the same symptoms. could you check to see if and when the GPU coils start having voltage on them? is it immediately on power-on or not?

sorry to use this thread for this question, but mine doesnt have GPU voltages, so am just asking to see where in the boot-phase it does that.
 
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tcampbell34

Member
Yea I still do not have external video. I tried to checked the GPU coils again and now I do not have any voltage on them for some reason. Before replacing U9800, I did have 0.9v on all the GPU coils.
 
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tcampbell34

Member
Ok so I replaced U9800 again and put the original one back on since I did not have another donor, and the GPU rails have voltage again now. I still have the same issue though with no image internal or external. EDP_PANEL_PWR_EN seems to only pulse for a few seconds after I connect the charger and then it just stays at 0v. Not sure what to check next.

Captianmac, the GPU coils on this board do get voltage immediately on boot. Hope this helps you.
 
2informaticos

2informaticos

Administrator
Staff member
"EDP_PANEL_PWR_EN seems to only pulse for a few seconds"
Check voltage at pins 44/45 of J8500 at same time.

Also check if DP_INT_HPD pulses.
If not, LCD voltages cannot be maintained.
In such case, try another full LCD assembly.
 
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tcampbell34

Member
I do not get anything on pin 44/45 of J8500 and also get nothing on DP_INT_HPD. I have tried 2 different full display assemblies and still have the same issue with both.
 
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tcampbell34

Member
When I first connect the charger, LCD_MUX_EN is 3.3v but LCD_MUX_SEL is only 2.5v. After a few seconds, LCD_MUX_SEL goes to 0v but the enable is still 3.3v. I'm pretty sure LCD_MUX_SEL is also supposed to be 3.3v but I am not completely sure on that.
 
2informaticos

2informaticos

Administrator
Staff member
LCD_MUX_SEL selects between CPU, or GPU video outputs.
You should check its level on working board, when boots.

PANEL_FET_EN_DLY pulses at same time with EDP_PANEL_PWR_EN?
 
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tcampbell34

Member
Yea LCD_MUX_SEL goes to 3.3v on boot and then goes to 0v after a few seconds and stays at 0v on a good board.

This board only seems to go to 2.5v for some reason. I tried to connect an external monitor to this board, and still have no external image, and LCD_MUX_SEL stays at 0v. PANEL_FET_EN_DLY is 0v and does not pulse at all.
 
2informaticos

2informaticos

Administrator
Staff member
2.5V is stil valid high level.
But such lower value can point to a problem with U9800/50.
Be sure R9856 is good.

Missing external video also points to U9800...
 
K

Ken

Member
Anyone get to the bottom of this? I have one non display external or internal and no power on coils for gpu
 
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tcampbell34

Member
I have not gotten to the bottom of this yet. I have GPU voltage but no image on mine. I know it’s not U9800 since I replaced it with a know good U9800 and still no image. I think it’s a PCH issue on mine
 
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tcampbell34

Member
So as a last resort on this one I put some flux around the PCH and heated it for only about a minute, and now its not booting fully anymore. I get 20v 250ma and seem to have all voltages except for CPU and GPU voltages. ALL_SYS_PWRGD is 3.3v and PPVCCSA_S0_CPU is 1.1v but PPVCC_S0_CPU is 0v. I noticed that U8605 seems to be getting warm now also but I could not find any shorts. I removed the plate/cover on J9600 and the amps drop to 190ma and U8605 does not get warm anymore. Could I have done some damage to J9600 during the PCH reflow or could a dead PCH cause this?
 
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