820-3476 x3!!!! NO image/display, but displays work AND external display works. Yes 3 mbp 13" a1502's same issue

[grmacs]

WOndering if this could be a firmware issue? what are the odds that I have 3 mbp's that power up and run external displays but show no image/backlight on known working displays. I was able to prove that all 3 of the displays work on other 2014 13"mbp.

0V of course on LCD connector pin 1. I can see the 3 backlight circuits on logics but no image at internal display connector either?

 

[grmacs]

WOndering if this could be a firmware issue? what are the odds that I have 3 mbp's that power up and run external displays but show no image/backlight on known working displays. I was able to prove that all 3 of the displays work on other 2014 13"mbp with their native lcd connector cables (that was my first suspicion is that they all had bad LCD cables).

0V of course on LCD connector pin 1. I can see the 3 backlight circuits on logics but no image at internal display connector either?

 

[SMMRepair]

Probably because you're using a 2015 model display. Lots of variables here...you need to rule them all out. "Known-good" displays--how do you know they work? Do they work with ANY 3536/3476 boards, OR do they work with any 4924 boards? This shouldn't be hard to figure out. Again, probably a 2015 display.

 

[grmacs]

None of them work with their own display. all 820-3476. I have an 820-3476 that works with all 3 displays and its own. All three that can't run their internal display I verified to work with external.

 

[grmacs]

I bought them all in one lot so I'm wondering if the three have some sort of custom firmware in them that caused them to have this issue. The one that works is an 8GB and the 3 that don't are 16GB but all are 3476 logics.

 

[2informaticos]

Apart of backlight. which other voltage did you check on LCD connector?
Keep in mind, backlight MUST appear after image; PCH needs to recognize LCD display first, of course.

5V must appear at pins 28-30 of J8300 in the first seconds (when chime), even if LCD is not connected.
If DP_INT_HPD goes high in that time, 5V should be maintained; as sign of PCH correctly recognized the display.

 

[grmacs]

This must be a firmware thing. Under the assumption I would get these working I loaded some drives using external display and the backlight came on. Still no image but the mac seems to see the display is there in the settings also. I'll post back once i've had a chance to try firmware.