820-2915 1/4 fan spin

Chuck60

Member
Hi I received a board and it had 1/4 fan spin
Replaced c7721 it was Still shorted then replaced u7720 and got the board working
Chime, booting, activity on screen but no backlight. After using dosdude gmux I still had no backlight replaced lp8550 and fuse
:( now the board is dead again I removed lp8550 and I have the
Same short on L7720 and u7720
I didn’t apply a lot of heat and was in and out quickly. What would give me the same short again? I’ve tested around u7880 and it’s not shorted also GPU isn’t in direct short. P.S. Board was running for most of the day and at J5650 pin 1 PP5v_S0 (fan connector) I have 5v but no fan spin :/ I also replace Q5502, Q5501 because they were missing
 
Last edited:

2informaticos

Administrator
Staff member
"activity on screen but no backlight. After using dosdude gmux"
Why did you touch GMUX, if had image???

What is the actual state of the board?
 

Chuck60

Member
Well
PPBUS_G3H is 12.53v
PP3v3_S3 =3.3v
PP5v_s3=5v
PP3v3_S0=3.3v
PP5v_S0=5v
PPDDR_S3_REG_R


PCH is Warm CPU is warm

I just flash Gmux in everyone of these Even if its working. just in case.
 

Chuck60

Member
L7220 =5v
PPVCORE_S0_CPU_PH1/PH2/PH3= 0v
PPVCORE_S0_AXG_L=0v

I had a issue on L7720 and that’s still .0v in diode mode to ground

what can kill this IC for a second time ?
 

2informaticos

Administrator
Staff member
My mistake, I wanted to ask about L7720, not L7220.

Can you post exact ohm value on L7720?
Lift it one side and see where the short remains.
 

Chuck60

Member
With removed L7720 and u7720
Pin 2 =260 ohms
Pin 1 =OL

I also removed Y5010
And put it aside

before removal of u7720 it was 0.v to ground On pin 1 with L7720 removed.
after removing U7720 pin 1 shows OL
 
Last edited:

2informaticos

Administrator
Staff member
260 ohm is far away of a short.
I didn't say to remove U7720; resolder it and check again ohm value at L7720 pin 1.
 

Chuck60

Member
Ok. I recheck R7720/21 one question can I power on this board wIthout u7720 and L7720? I wanna make sure there’s no spikes on 3v3_s5 that might kill it again
 

2informaticos

Administrator
Staff member
Yes, you can.
But U7720 should be the last you afraid of 3V3_S5 spikes.
SMC and PCH are directly connected there, and much more sensitive...
 

Chuck60

Member
Ok fan spinning ,Chime. Steady 1.8v now on to backlight issue. One question is there a downlink for MRI (resource inspector)
 

Chuck60

Member
Yes I have image no backlight. I have all the enable signals. The resistors on the voltage divider are good and capacitor isn’t shorted. The voyage is 11.53v at gate of mosfet. I believe the mosfet isn’t sending it to ground. But I dont have the part# on my phone it’s on the notepad at home. I’ll get you all the specifics Part# when I get back home.
I did google mri but I’m confused as to which one is the right link. I found these which is one you’d consider downloading? Or if you have the site and you can point me in the righT direction That would be greatly appreciated
 

Attachments

Chuck60

Member
BLK_EN =3.1v
Blk_PLT_RST_L=3.3v
LCD_BKLT_EN=3.3v
LCDBKLT_EN_DIV=4V
BKL_PWM=2.5v resistor is 33ohm
I’m thinking Q9706 is bad :/
 
Last edited:

2informaticos

Administrator
Staff member
"LCDBKLT_EN_DIV=4V"
You should have (at least) PPBUS_G3H voltage at L9701.
If not, Q9706 is bad.
Be sure no short to grround at D9701 pins; with LCD connected, of course.
 

Chuck60

Member
Ok so I test for voltage at c9797 and got 0v D9701 tested good Q9706 Was internally shorted replaced Q9706 and have 40v at C9797&C9799 but not at C9000 or pins 38,39,40 on lvds connector tried running 30awg from C9797&C9799 to pond 38,39,40 and got no backlight. Resistance to ground on these pins reads “OL” Is this gauge Of wire to small? I see there’s some sort of filter but it looks like it’s internal :/
 
Last edited:

2informaticos

Administrator
Staff member
Rebuild the trace correctly.
Check connector and video cable for damage.

40V seems to be correct voltage for this 15" model.
Usually voltage goes higher than 50V if LEDs strip don't make contact.
 
Top