820-01700 comes only backlight. please help

[Dozer]

got this device with a strange problem. connecting batterie, open lid, connecting power .

20V, amper is rising up until about 2.8A
then it switches to 19.8V like always, display backlight is coming up and that is all !

i checked the whole board no water damage to see or any other strange things, hecked the edp-connector with the mac edp-meter, all ok.
checked the NAND power 2.52V both sides, checked external display, same hdmi is detecting the signal, monitor turn on but no picture to see only a light black

reballed the U9850 no change

what is the next step usually after turn on backlight?

 

[Dozer]

I only need user-data. I tryed to set Target mode but nothing. PRAM reset seems not possible and there is no chime

 

[Dozer]

it turns on like described and from turning on backlight after 34 seconds it turns off and all starts from beginning, that is cycling.
I checked the NAND power but this is without interuption steady 2.52V

I found out still another intresting thing. by connecting the touchpad the display comes up only for about 1 second. i thought the pad is faulty so i replaced it and the cable but result the same, with touchpad 1 second, without 34 seconds

 

[2informaticos]

Still restarts if you turn it on pressing T key?
Even no image, check if its SSD is detected in another MacBook.
You may need to use thunderbolt capable cable.

Tried DFU revive?

 

[Dozer]

thanks for your replay.
still restart (all 34seconds) by pressing T key or not
I will try to get it in DFU mode, is it needfull to connect the trackpad?

 

[Dozer]

connecting a real known DFU working thunderbolt cable in the left USB port near trackpad and connecting battery and shorten SWK003 by plug in power shoul do this yes?

 

[Dozer]

get DFu but during revive step 4 half way it turns on, only backlight, then I get this

and it stays in this mode (on only backlight, dont turning off) after disconecting thunderbolt cable it turns off. after that it dont turns on for 34 seconds, it do nothing. get back in DFU mode this time with conected trackpad. step 4 half way display turns on for a second then i get this symbol like a lock.

but now it is cycling again display on 34 seconds, off and so on....

 

[Dozer]

before i wrote her , 2 weeks ago i got a working a2141 i replaced the board with this one and got a sign battery empty, but only one time all the other trys were the same like this and before replacement. i checked the good board in the case of this board there was all ok.