820-00840 no image

[Gadget Labs BH]

Hey guys, I have an 820-00840 with no image.

• External monitor DOES work.
• The image is not dim, it is non-existent.
• Tried 3 different displays and eDP cables.

With display connected:

• LCD_IRQ_L - 10.00 mV
• DP_INT_HPD - 10.00 mV
• PP3V3_S5_LCD - 5.13 V
• PANEL_P5V_EN - 0 V (checked on test point and R8515 and C8515)
• EDP_PANEL_PWR_EN - 0 V
• BUF_EDP_PANEL_PWR_EN - 0 V

 

[2informaticos]

First of all, welcome to the forum!

Any history available?
Liquid signs at LCD connector?

 

[Gadget Labs BH]

First of all, welcome to the forum!

Any history available?
Liquid signs at LCD connector?

Thanks!
No signs of liquid damage. LCD connector looks good. Came in for LCD replacement because of no image and previous LCD was cracked and had no signs of life. New LCD didn't fix the issue.

 

[2informaticos]

Check the other LCD connector in the case; where the small flex from MLB gets connected.
Did someone else work on it before?
Check for knocked of components, near the screw areas.

Please, do NOT quote an entire post visible few centimeters above.

 

[Gadget Labs BH]

It looks like it has been worked on before.
D8518 near U8501 was knocked off but I replaced. Also replaced U8500 and U8501 to be safe.

 

[2informaticos]

Probably more damage on the board.
You should check all traces and be sure about solders.
We need some voltages on LCD connector (screen connected).

 

[Gadget Labs BH]

Are you suggesting I check my U8500, U8510, and D8518 solders?
I did do a thorough inspection on the board and I see no other places that seem to have been tampered. I do notice the area around L2990 gets a bit hot but can't find a short and voltages are normal.

 

[2informaticos]

Check diode mode readings for all EDP_INT_ML_x lines; good to have working board for comparison.

R8554 is good?

 

[Gadget Labs BH]

0 V on R8554, diode readings for all EDP_INT_ML_x lines is OL.

 

[2informaticos]

Recheck puting red probe to ground; and remember this, when you check diode mode!
And check w/ and w/o LCD connected.

"0 V on R8554"
I just asked if resistor is good, as ohm value.
You said 0V and no idea which pin you've measured.
A bad resistor can have correct voltage on one pin and 0V on other...

 

[Gadget Labs BH]

R8554 is 0 ohms.
Diode reading were tested with red probe on ground.
Everything EDP_INT_ML_x is OL

 

[2informaticos]

I just saw this board has separation caps; so correct OL values.
In sthis case, the caps also protect against overvoltage on LCD connector.

"PP3V3_S5_LCD - 5.13 V"
Are you sure about this?

Check if you get at least a pulse at PANEL_P3V3_EN in the first seconds, when board boots.

 

[Gadget Labs BH]

5.13 was an error. It's 3.32.
I do get a quick pulse in the first 10 seconds on PANEL_P3V3_EN 3.35v. Tested at C8516 pin1 and R8590 pin1.

 

[2informaticos]

You should get corresponding voltage at pins 44/45 of J8300 at same time; confirm that.
If yes, DP_INT_HPD must pulse too; LCD connected, of course.

 

[Gadget Labs BH]

45 gets a pulse at 5v but 44 gets nothing. DP_INT_HPD gets nothing. R8501 ohms was low so I replaced. Still nothing.

 

[2informaticos]

U8500/01 are both enabled by the same signal.
Compare reactions at their pins.
Do you get 3V3_S5_LCD?

 

[Gadget Labs BH]

Ok, just got 45 and 44 to pulse at 5v and 3v respectively.
3V3_S5_LCD is 3.3
DP_INT_HPD pulses at .800V at first few seconds.
PANEL_P3V3_EN pulse at 3.35v
BUF_EDP_PANEL_PWR_EN pulse at 3.35v
BUF_EDP_PANEL_PWR_EN pulse at .800v

 

[2informaticos]

You should test with an o-scope, it can show exact peak pulse value.
If DP_INT_HPD pulse to 3V, means LCD replies correctly; PCH should recognize its presence.

Be sure BUF_EDP_PANEL_PWR_EN also has 3V peak pulse.
If not, change U8510.