A1707 820-00928-A no backlight

H

hgoncalves

Active member

Oct 10, 2025

• #1

Hi.

I've got an A1707 820-00928-A without backlight.

The mac seams to boot, I have CAPS activity, but 0V on PPVOUT_S0_LCDBKLT and 1.1200 on diode reading.

I've already tried with a good display, but same result.

Should I replace U8400 or is there any tests to make before?

 

2informaticos

Administrator

Staff member

Oct 10, 2025

• #2

Is there internal image for sure?

 

H

hgoncalves

Active member

Oct 10, 2025

• #3

Well, I'm not sure. How can I be sure?

 

2informaticos

Administrator

Staff member

Oct 10, 2025

• #4

Do you get 3V3/5V_S0SW_LCD?

 

H

hgoncalves

Active member

Oct 10, 2025

• #5

Yes, i have both 3V3/5V_S0SW_LCD

 

2informaticos

Administrator

Staff member

Oct 10, 2025

• #6

Check DP_INT_HPD; LCD connected.
Also check diode mode at J8500's pins 1 & 3.

BTW, do you get external video?

 

H

hgoncalves

Active member

Oct 13, 2025

• #7

Hi.

DP_INT_HPD = 0V

J8500 diode reading:
1= OL
3= 0.179

I tought I had external video, but now I don't have external video with the board alone on the desk

 

Last edited: Oct 13, 2025

2informaticos

Administrator

Staff member

Oct 13, 2025

• #8

"1= OL
3= 0.179"
Did you check both with red probe on ground?
You should get very similar readings.

 

H

hgoncalves

Active member

Oct 14, 2025

• #9

Hi.

I've confirmed and those values are correct:

J8500 diode reading:

43 = 1.189
1= OL
3= 0.179

 

2informaticos

Administrator

Staff member

Oct 14, 2025

• #10

Bad trace to pin 1?
However, 0.179 looks lower than expected at pin 3.
You should change U9850.

 

H

hgoncalves

Active member

Oct 14, 2025

• #11

I've replaced U9850 and now I have 0.495 on pin 1 & 3 of J8500, but still no image.

 

2informaticos

Administrator

Staff member

Oct 14, 2025

• #12

DP_INT_HPD still 0V?
Tried known good LCD assembly again?
External video missing now?

 

H

hgoncalves

Active member

Oct 15, 2025

• #13

Hi.

DP_INT_HPD still has 0V and no external video.

 

2informaticos

Administrator

Staff member

Oct 15, 2025

• #14

What about CPU core voltage?
Can you confirm Caps Lock reaction, or USB activity?

 

H

hgoncalves

Active member

Tuesday at 3:29 PM

• #15

I have 1.2V on CPUCORE_SW1/2, and no CAPS nor USB activity.

No big coil seams to be shorted.

However, I had CAPS before. Something happend in the meanwhile.

 

2informaticos

Administrator

Staff member

Tuesday at 4:18 PM

• #16

CPU core should drop to 0.6-0.85V, when machine boots.

 

H

hgoncalves

Active member

Wednesday at 11:02 AM

• #17

Hi.

It doesn't drop from 1.2V. Can I assume a dead CPU?

 

2informaticos

Administrator

Staff member

Wednesday at 5:01 PM

• #18

PCH, CPU, BIOS.
Just in case, try known good BIOS.