Display flickering after login 820-00165

Hey guys,
I have an issue that I'm hoping someone can please help me with.
It is an 820-00165 which has a flickering display after logging in. During startup, the apple logo is displayed and the machine loads to the login screen. After logging in, just before the loading bar completes, the screen starts flickering. It appears to be the screen itself, not the backlight but I could be wrong.
External display works with the screen plugged in or not.
I have tested with another known good screen, IO board and cable and have removed the board from chassis.
No physical damage can be seen. LVDS looks clean and continuity between pins and caps/resistors is fine but I have touched up the joints to make sure. I have also reflowed U7701 but have not yet replaced it. I have replaced C8324 because it looked a little funny but no change.
Diode readings on LVDS connector all seem roughly .050 or .060 below values shown on logi.wiki.
Here is a video of the issue.

Thank you very much for reading.
Last edited:


Staff member
First of all, welcome to the forum!

Do PRAM reset 2-3 times.
Just in case, test with USB macOS; it helps to discard a software issue.
See what happens starting in safe mode.

Check for fluctuations at 3V3_S0SW_LCD and DP_INT_HPD.
ALso check at both pins of D7701.

BTW, stop using LVDS as we have an eDP bus instead here...
Thank you! Long time listener, first time caller. I appreciate you taking the time.

I have reset pram repeatedly and have tested with a test internal OSX drive as well as external USB Linux platform. The problem presented itself in both cases. Is this sufficient or should I try USB osx too?

I will try safe mode and get those measurements asap and let you know.

Sorry! eDP it is.
Safe mode does the same thing but hangs on login loading page much longer

3V3_S0SW_LCD = 3.298V steady
DP_INT_HPD = 2.692V steady
D7701 - pin1 = 8.57V pin2 = 24.63V and both steady


Staff member
Did you take these voltages when the screen starts to flicker?
Need to know their values then.

If external monitor works good, then should be a problem with CPU eDP output.
An iGPU core problem should affect external video too.
Also looks like the problem appears when the video driver is loaded.
Try Windows 10 Live USB, which will use a generic video driver only.
This kind of Live distro should have memory tools embedded; do a RAM test, if possible.
Yes, I waited until the flicker was happening to take those measurements.

I did a ram test a few days ago using memtest for 4 full passes and got no errors. I tested it to be thorough but i also figured it would affect the memory reading in the system specs or the system functionality as a whole.

I kind of landed on it being a CPU issue after everything seemed normal around the display/backlight circuit but I couldn't shrug the feeling that a cpu issue would again, affect the functionality of the machine. Everything else is running perfectly and that's why I felt like I needed an expert opinion. I know this is a weird one so again, I appreciate your help so far.

I will let you know what happens with Windows2go.
The theory about the video driver seems correct. Windows2go boots and the machine passes in-platform memory/cpu/2d graphics tests.
Things fall apart when the graphics driver is loaded and the screen starts flickering again.
It did seem odd to me. When I had nothing else to point to, I was thinking, if it were an integrated graphics issue, it should affect external display too.
Could it just be a cold joint somewhere on the cpu? Worth a reflow or an extra ultrasonic just in case or is it more likely to be a cpu ic fault?


Staff member
As I said, strange issue affecting only internal eDP bus.
But no doubt is iGPU issue, once problem appears only when driver is loaded.

You don't lose anything heating CPU for test; but do not expect a miracle.