820-2915-B turn on, no video

[HOSOI]

Hello, this MP turns on, charge, have green and orange light at MagSafe, but there is no video and no chime either, there is no sign of water or burned parts, flashed the spi just in case and nothing, removed the ram and no beep, connected external monitor and nothing. any clue where to start?

BR

 

[2informaticos]

Post VCORE level.
Do you get all other voltages?
PLT_RESET_L goes high?

 

[HOSOI]

PLT_RESET_L __3.34
PP5V_S5__5
PP5V_S3__5
PP5V_S0__5
PP3V3_S4__3.34
PP3V3_SUS__3.34
PP3V3_S5__3.34
PP3V3_S3___3.34
PP3V3_S0__1.34
PP1V8_S0__1.77
PPVCORE_S0_CPU__1.14
PP3V3_S0GPU___3.34
PPVCORE_GPU___1.11

 

[2informaticos]

When board boots, VCORE must drop to 0.75V aprox.
Try one known good DDR module, one slot at a time.
I'm not sure if works with PC3-8500; try 10600, or 12800, just in case.

 

[HOSOI]

VCORE drops to 0.75 without the battery connected and just the display and ram on it, but with the battery connected, the display, and ram it drops to 1.06. is that normal?

 

[2informaticos]

Let the battery out for the moment.

VCORE drop looks like board boots.
You may have GPU issue.
Should be good to disable GPU in BIOS, just for test.

 

[HOSOI]

that sounds in part good. Sorry for my ignorance but how can I disable the GPU in BIOS?

 

[2informaticos]

Medusa programmer knows to do it.
If you don't have it, upload original BIOS somewhere.

 

[HOSOI]

Hello, thank you for your valuable help, unfortunately, I don't have medusa yet. if is not too much to ask you, how can you do that with the .bin file? is there a guide for that? I'd like to learn ho to do it.

https://drive.google.com/file/d/1zwrXl1b5tBnedsh_qexrI70pB6f5DP_x/view?usp=sharing

BR

 

[2informaticos]

Try this file.

w80305acagu no gpu.rar

drive.google.com

Don't forget to remove first R8904/11; at least one of them.
Be aware, do NOT do PRAM reset.

 

[HOSOI]

nothing happened sr. Everything still the same. no video at all, I confirmed that there is mouse activity, noticed that the DVD ROM is not powering on, before flashing it was. I also tried an external monitor just in case. I'm curious about something, why there is no beep when there is no RAM? as I know it should, please correct me if I'm wrong. thanks.

 

[2informaticos]

If board can't boot, no RAM error posibble.

BTW, modded BIOS disable external video.

Did you remove mentioned resistor, before applying power?

 

[HOSOI]

of course, I lifted one side of each resistor.

in this case what next? flash the original bios back?

 

[2informaticos]

Looks like no GPU problem.

BTW, GMUX was touched?
Check if JTAG pins next to GMUX have been used.

 

[HOSOI]

everything is intact there.

 

[2informaticos]

If VCORE still drops to 0.75V, then check for USB activity.

 

[HOSOI]

yes, VCORE drops to 0.76, and there is USB activity I connected a USB ethernet adapter and I have link on the adapter and the switch as well, but like I said is weird cuz if I remove the ram I dont get the beep for no ram on it and I also have usb activity without ram. I did smc bypass and the fan spins faster. what else should I do or test?

 

[2informaticos]

Impossible to have REAL USB activity without RAM.
Without RAM, VCORE should stay higher.

Use macOS USB pendrive with Link LED; if flasshes there is USB activity.

 

[HOSOI]

with the USB pen drive there is no activity, and yes without ram VCORE stays high, so what next then.

 

[2informaticos]

Did you test the board alone on the desk?
Connect only charger and USB tester; maybe speaker too.