820-3662 no video on internal display

jgraffis

New member
I've got this 820-3662 that shows no video on the internal display. i get 0v on L8300 so i checked back at u8300 and have 0v on pin 1 which is the power on pin for u8300. i get 0v on PPVOUT_S0_LCD/BKL/T. I don't think this machine is seeing the lcd but not getting voltage on u8300 is making me think of u1100 not working properly.
i did reset the PRAM and smc
 

jgraffis

New member
yes it has external video. the screen I'm using is from a working machine. i did test continuity on the connector threw a good cable also, so don't think its a connector issue.
 

jgraffis

New member
yes all caps are present c8320,c8321,c8322,c8323,c8324,c8325,c8326,c8327. all of the coils, fl8300,fl8301,fl8302, fl8303 are present and have continuity. i beginning to wonder if my test screen shit the bed. i tested all pins for short to ground with screen plugged in and only had ground on the pins that its supposed to be on, i did have 0L on all the data lines though. not sure if that is supposed to be correct?
 

dukefawks

Administrator
If you do not know your test LCD is good then I cannot help further. First thing is to have a 100% known good part for testing.
Do check if there is a short burst of power on L8300 right on start up.
 

jgraffis

New member
ok, back to this one for me. i did get a known good tested screen for it and still same issue. it does have a short burst of 2.9v on l8300 then goes back down to 0.0v. not sure what this means. maybe a bad cap in the line?
 

jgraffis

New member
i was able to run ASD and yes it had a symbol error( but i didn't have a screen connected) SMC_LID area seems just fine looking. it also failed for 6 other issues also. the one i was thinking is not correct is
sensor- current (IO5R) 5V Rail Highside --- sensor reads below the low limit.

when i tested for voltage at pin 6 of u5420 i got 0.040v. i did get 3v on pin3, and 12.5v on pins 4-5. i also check the resistors and they check out just fine. I'm thinking maybe U5420 is screwed up?

the next 3 were battery temp test( again not plugged in)
the next 2 were ssd temp test( again no plugged in) but strange
 

dukefawks

Administrator
So you tested without LCD connected......what good does that do? As for the sensor issue it's reading low cause there is no LCD puling current on the 5V bus.
 

jgraffis

New member
Shit wasn't thinking on that one. i retested with everything plugged in. ASD OS fails for
sensor group test- limit load test. error -1 unknown error
ASD EFI fails for
display port symbol error test - error- Lane count is zero
sensor temperature (th0a) -- SSD A sensor is reading below low limit
sensor temperature (th0b) -- SSD B sensor is reading below low limit

these seem strange because i i used the thunderbolt ports to run ASD on external
 

dukefawks

Administrator
Bad connector? Measure continuity from a separate LCD cable the the caps/coils. Also do a diode mode test on the eDP caps on the CPU side to check for continuity to the CPU.
 

jgraffis

New member
I went ahead and replace the connector and check for continuity like you said and everything was fine there. I did diode mode test on R0530 pin 1 reads out as 0.015v pin 2 0.030v. also noticed that i do get a pulse of 5v on L3800 then back to 0.0v. Not really sure whats going on with this board.
 

dukefawks

Administrator
Only thing that is left is a CPU issue I'm afraid. Last thing to check is voltages in R0531 and diode mode.
 
Last edited:
Top