(347) 552-2258 [email protected]

820-3115 - Hissing/ticking noise by the lvds connector

Alan.L

Alan.L

Member
board was liquid damaged. no green light when try i to power it on and Hissing/ticking noise can be heard by the lvds connector.
SMC was shorted to ground, so i removed and replaced the SMC. but Hissing/ticking noise is still there.

board now turn on and passed ASD. where is the noise could coming from in that area?
 
Last edited:
D

dukefawks

Administrator
Backlight coil, remove backlight fuse and see if noise is gone. Then check all resistors/caps/LP8550. Only mess with this if it really is an issue, I would probably not bother if everything works.
 
Alan.L

Alan.L

Member
noise is still there after i removed the backlight fuse. noise is not coming from the backlight coil, i can hear the noise below the coil area. it is audible.

LP8550 area it is all good. i have no problem showing backlight and images on screen.

also i notice something strange. i have to replug magsafe connector multiple time in order to get a green light. it can charge and detect battery info on OSX fine.
after i get green light, i can turn on and off and repeat no problem. how i check if i did a good job on SMC? this is actually my first time replacing a smc which seems to be 1st success otherwise...

PPBUS_G3H =12.52V
PP3V42_G3H = 3.52v
PPVRTC_G3H = 3.3v
PP5V_S5 = 4.93v
PP3V3_S5 = 3.32v

3.52v on PP3V42_G3H seems little high than usual.


Resistance between pin 17/18 and 27/28 of the ISL6259
4 ohms on pin 17/18
22 ohms on 27/28
 
Alan.L

Alan.L

Member
sorry it is actually very dim green light.

Yes...

PPBUS_G3H =12.52V and 3V42 = show 3.52v


i replaced u6990, d6990 before because it had corrosion.
 
Last edited:
D

dukefawks

Administrator
The green light issue is probably the magsafe board, swap it with known good one.
Measure the voltage on pin 1 of R7081 and 7086.
 
Alan.L

Alan.L

Member
already tried another magsafe board and still same.

dim green light
16.05v on pin1 of R7081
6.80v on pin1 of R7086

when power on with green light
6.3v on pin1 of R7081
6.70v on pin1 of R7086
 
Last edited:
Alan.L

Alan.L

Member
they are good.

i'll have to do it tomorrow. i need to get some sleep. thanks :)
 
Last edited:
D

dukefawks

Administrator
Before touching anything I want to know what voltage is on pin 2 of R7081 when there is no green light. If it also 16V then there is an issue with the U7000 circuit most likely.
 
Alan.L

Alan.L

Member
dim green light.

15.92v on pin2 of R7081
16.01v on pin1 of R7081


with green light.

0.019v on pin2 of R7081
6.3v on pin1 of R7081


i think there is also noise coming from this area as well.
maybe i should ultrasonic this board..



thanks duke, i;ve catch you tomorrow.
 
Last edited:
D

dukefawks

Administrator
Yeah U7000 is not pulling down R7081. This could have a bunch of reasons, a clean would be a good place to start.
 
A

arghhh

New member
I have also seen a bad U6990 cause high voltage on pp3v42. It also kept causing R6990 to blow until I replaced U6990.

I would compare resistance to ground on pin 1 on C6991 to a known good to make sure it is not partially short, then check R6990 and replace U6990 again just for good measure.
 
Alan.L

Alan.L

Member
ok, i've ultrasonic the board, still no good and noises are still there.

i've even replaced u7000. no affect.

U6990 had been replaced before. maybe i had a bad one from donor board?

R6990 is fine.
 
Alan.L

Alan.L

Member
replaced U6990, Q7030, Q7035 and still same problem.


also notice after go green light, sometime go back dim. not all time tho.
 
Last edited:
Alan.L

Alan.L

Member
Not sure why...replacing these 3 components made it worst. Now the fan is pulsing after few mins from turning on.

i'll put the original back...
 
Last edited:
Alan.L

Alan.L

Member
weird. the original fan, sometime pulsing or not moving at all. i then put in a different fan. it start slightly slow then normal speed. original fan work fine on know good boards.

please watch my video

you can hear the hissing noise as well.
 
Last edited:
You must log in or register to reply here.
Top