820-00239 No video on panel or external monitor

joshAU

Member
Hi all.
First, I'm not familiar with working on this model board.

No video on internal panel or externally on any USB C port with a USB-HDMI adaptor that I've had working in other Macbooks.
No fans, no chime.

No signs of any liquid damage on either side of board.

Power rails seem good, CPU gets hot, USB hard disk gets flashing light on it.
Tried with another AC adaptor, both with and without battery connected.
Tried SMC reset.
Tried on external panel with internal disconnected, and tried other internal panels.

PPDCIN_G3H IS 22v.
PPBUS_G3H, HS_CPU, HS_OTH5V, HS_OTH3V3, S4_HS_TPAD are all 14.v.
PP3V0_G3H IS 3.4v.
PP3V3_G3H, S5, SUS all 3.7v.
PP5V_S5, S4, S0 all 5.7v.

Any suggestions appreciated.
Thanks.
 

2informaticos

Administrator
Staff member
Seems to have low battery on your multimeter.
Change it and post CPU core voltage when you get flashing USB device.
 

joshAU

Member
lol, good diagnosis there 2informaticos in regards to the low battery on my multimeter!

OK, after replacing the battery in it, here's the CPU core voltage:
When I press the power button, about 3 seconds later, PPVCC_S0_CPU goes from 0.0v up to 1.14v
About 3 seconds later, that voltage drops down to 0.71.
And then seems to remain there.

When I plug in the USB memory stick with a light on it, and when its flashing, the voltage is the same,0.71 volts.
 

joshAU

Member
I had tried disconnecting internal LCD, but still no external on any of the USBC ports.
I retested, on all 4 USBC ports, with two different USBC-HDMI adapters that we use regularly on other macbooks.
 

2informaticos

Administrator
Staff member
Missing internal/external video at same time points to graphics issue.
Unfortunately, this board doesn't have dedicated (discrete) GPU; so should be iGPU problem.
Check diode mode to ground on all EDP_INT data lines of J8500.
 

joshAU

Member
OK.
That makes sense.
Thanks again for your help.

With the screen disconnected, red lead to ground, all seem to read around 256:
Diode mode to ground readings:

EDP_INT_AUX_N 254
EDP_INT_AUX_P 257
EDP_INT_ML_N<0> 256
EDP_INT_ML_P<0> 257
EDP_INT_ML_N<1> 255
EDP_INT_ML_P<1> 256
EDP_INT_ML_N<2> 257
EDP_INT_ML_P<2> 258
EDP_INT_ML_N<3> 255
EDP_INT_ML_P<3> 256
 

2informaticos

Administrator
Staff member
Not sure if CPU core should remain at 0.7V or should drop to 0.6V.
If you get USB flashibg, board looks to work.
Caps Lock light reacts too?
The chime comes back after PRAM reset?
 
Last edited:

joshAU

Member
Hi again.
I rechecked CPU core - goes to 0.69v then stays there.
I get USB light flashing on all 4 USBC ports.
Yes, Capslock light works correctly.
Touchpad does tap correctly when unit is turned on.

NO Chime after PRAM reset - no chime, ever.
No fans, ever.

The macbook appears as a disk correctly when I put it in target disk mode.
 
Last edited:

joshAU

Member
Thanks again 2informaticos.
I only have a CH341A programmer, with a standard 8 pin SOIC adapter.
To load a good BIOS, do you have to manually solder wires to the board, or is their an adapter I can just plug in?
Never programmed a Mac BIOS before.

And, given I can get the unit to boot in Target disk mode, can you flash the BIOS via target disk mode, using Apple Configurator, or by some other means?
 
Last edited:

2informaticos

Administrator
Staff member
If you plan to stay in business with Apple boards, buy Medusa programmer; with necessary set of adapters.
Other programmers able to connect directly to J6100 are available to buy also.
Years ago I posted fotos about how to solder WSON chip on small SOP-DIP adapter which comes with classic adapters (like CH341).
 
Top