820-3115-b - weird graphics problem

Anterweb

Member
This came in for a service and ssd upgrade, customer said it was slow and kept hanging.

Board was filthy inside so put it through the ultrasonic added the new ssd and some ram but when installing os I noticed some weird graphic stuff going on, like blocks for a courser and then (see image) 20220514_194747.jpg

Looking through the forum I see a few posts relating to graphics on this model and numoros solutions..
Any advice on the best fix for this appreciated.
 

2informaticos

Administrator
Staff member
There is no dedicated graphics, just iGPU embedded into CPU.
You may have problems with CPU, or RAM.

Test the board with one RAM module at time.
Did you test external video?
 

Anterweb

Member
So I changed the ram to a single known good 8gb stick and swapped out the new ssd for a known good working one,
Also noticed it does have a separate dedicated AMD graphics chip aswell as the igpu Intel one,

When first trying to install os it did again some weird graphic stuff (see pics) both on built in screen and external, but after os install and updating it seems to be running OK? Although it does seem to be running hot and the fans are kicking in hard from time to time.

I've had it running a full screen 1080 video for over an hour and it's still OK, should I consider this fixed or should I disable the AMD graphics? (if yes what is now the preferred method?) Or is there a better way of stress testing this before giving it back?
Again thanks for your help on this.

20220515_163659.jpg

20220515_153042.jpg20220515_151349.jpg20220515_150310.jpg20220515_150456.jpg
 

2informaticos

Administrator
Staff member
You have the option to disable AMD GPU, if still note problems.
Unigine Heaven benchmark is very good for GPU stress test.

I recommend to disable GPU flashing the GMUX.
If you do it in BIOS, set EFI password; to avoid accidental PRAM reset.
BIOS mod isn't PRAM resistant.
 

Anterweb

Member
"I recommend to disable GPU flashing the GMUX"

This is a new one on me, any guides on doing this anywhere as I'm keen to learn how,
Thanks for the info! Again ur a legend, I've learnt so much from you guys the last 2 months, much appreciated.
 

Anterweb

Member
After doing my homework it appears that buying a Lattice HW-USBN to flash the GMUX is by far the easiest and fastest solution for these machines,
But is the file required to flash the GMUX something I can get here , Or would I have to pay for a license for it each time I have one of these I need to flash?
 

Anterweb

Member
Dude, I'm finding serval different places to get this file, am I correct in thinking the one that seems easily available does work ok but after flashing you can no longer use the toggle brightness keys on the keyboard? also is there any other common bugs that occur after flashing the GMUX?

(I have ordered the lattice programmer and am just waiting for it to arrive )
 

2informaticos

Administrator
Staff member
Tiresias GPUKiller is the best.
It preserves keyboard controls for backlight.

GMUX flash, as BIOS mod too, don't allow backlight control.
 

Anterweb

Member
Tiresias GPUKiller Looks like the perfect / easiest solution. sadly these Tiresias chips cost more than this model of mac is worth or sells for here in the UK!!! :eek:

Ill give the GMUX a bash when the programmer arrives!

Thanks dude
 

2informaticos

Administrator
Staff member
Flashing GMUX is the fastest way; no need to remove the MLB from its house.

BIOS mod takes time to desolder/resolder SPI chip and doesn't resist to PRAM reset.
Keyboard control is still active under old macOS versions; doesn't work since High Sierra.
Also need to force enable/adjust backlight signals, to avoid sleep/wake problems.

I didn't test the control for GMUX flash under El Capitan.
However, in both cases, software control can create a backlight adjust impression.

The perfect fix is Tiresias GPUKiller.
If I correctly remember, Harald makes good discount buying in bulk.
And he has many other interesting tools in his store.
 

piernov

Moderator
Staff member
GMUX firmware mod can still do brightness adjustment with either PCH microvia jumper (software and keyboard control, soldering is risky to perform), raw keyboard signal (no software control, some jumpers required) or custom driver (software and keyboard control, no soldering required), depending on the custom firmware applied to GMUX.
 

Anterweb

Member
This is fab info thanks so much, my programner is going to take a while to get here so is there any reccomnded sources for gaining the info and files required to carry out this GMUX flash while maintaining brightness control?
 

2informaticos

Administrator
Staff member
There must be a test point (the opposite board side I think), which avoid the risky solder onto PCH package.
 
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