MacBook 2011 A1286 power cycle, no chime

[durchfall]

I have a MacBook Pro 15" late 2011, it has a dead GPU and was sent to a repair center for this issue multiple times, the last time the original owner of this machine decided to not fix it anymore. The repair center returned the machine, but they desoldered the GPU and VRAM, it just physically isn't there anymore. The machine did originally work, we'll get to it.
What it does now: does not turn on in SMC bypass mode, the fans just twitch and I can hear a ticking sound from the board, almost like there was a short circuit. But in normal mode it does start, fans spin for about 10 seconds, power light glows, no chime, then fans stop spinning for about 5 seconds, then they spin up for 10 seconds and this cycle just repeats. If I start it without RAM, fans stay spinning indefinitely and it does beep as it should. Both CPU and PCH are getting warm. I checked for shorts, couldn't find any. There is no visible corrosion on the board. I measured voltages, all measurements were done with battery disconncted, here are the results:
PPBUS_G3H 12.6V
PPVIN_S5_HS_COMPUTING_ISNS 12.6V
PPVIN_S5_HS_GPU_ISNS 12.6V
PPVIN_S5_HS_OTHER_ISNS 12.6V
PPDCIN_G3H 16.5V when fan spins 16.2 when fan doesn't spin, battery disconnected
PP3V42_G3H 3.48V
PPVRTC_G3H 3.35V
PP5V_S5 5V
PP5V_SUS 5V
PP5V_S3 5V
PP5V_S0 5V
PP3V3_S4 3.35V
PP3V3_SUS 3.35V
PP3V3_S5 3.35V
PP3V3_S3 3.35V
PP3V3_S0 3.35V
PP3V3_T29 3.35V
PP1V05_T29 1.03V
PP15V_T29 0.5V not shorted (84kOhm)
PP1V8_S0 1.8V
PP1V8_S0_CPU_VCCPLL_R 1.8V
PP1V5_S3 1.5V
PP1V5_S3RS0_CPUDDR 1.5V
PP1V5_S0 1.5V
PPVTTDDR_S3 0.75V
PP0V75_S0_DDRVTT 0.75V
PP1V2_S0 1.2V
PP1V05_SUS 1.05V
PP1V05_S0 1.05V
PP3V3_S0GPU 3.35V
PP1V8_GPUIFPX 1.8V
PP1V8_S0GPU_ISNS 1.8V
PP1V5_GPU_REG 1.5V
PP1V5_S0GPU_ISNS 1.5V
PP1V0_S0GPU 1V
PP1V0_S0GPU_ISNS 1V
PPVCORE_GPU 1.1V
PPVCORE_S0_CPU 1.15V
PPVCORE_S0_AXG 0V no short, should just mean it's not getting far enough in POST
PP1V5_S3_CPU_VCCDQ 1.5V
PP1V05_S0_CPU_VCCPQE 1.05V
PPVCCSA_S0_REG 0.8V
PPVP_FW 12.65V
PP3V3_FW_FWPHY 3.35V
PP1V0_FW_FWPHY 1V
PPBUS_SW_BKL 0V no short, probably just doesn't get far enough to initialize backlight
PP3V3_ENET 3.35V
PP1V2_ENET 1.2V
ALL_SYS_PWRGOOD 3.3V
SMC_RESET_L 3.47V
Some more info: This machine used to belong to an ex colleague who left it at work, so I decided to take it. I installed macOS on a different machine, deleted radeon kexts and enabled screen sharing. I swapped the drive into it, let it boot up with a blank screen, remoted into it and wrote NVRAM parameters to enable IGP. It did work just fine after that. Then I decided to upgrade RAM, so I did and when I powered it on afterwards, it started doing the power cycle loop thing. As I already said, a repair canter physically removed both the GPU and VRAM. They didn't clean up, pads still had solder balls and a ton of flux. So I cleaned the pads with some solder wick and used alcohol to get rid of the old flux. No change, still power cycling. So I left it do its power cycle thing, after about 10 minutes it suddenly chimed and started right up. So I shut it down, upgraded RAM, turned it on and after about 10 minutes of power cycling, it started. But the next day it wouldn't start even after two hours. I tried desoldering R8911 to disable GPU power completely, that changed nothing. So I ran a bodge wire to reenable GPU power, again, no change. The machine did originally start even in SMC bypass mode btw, in the brief time it worked. It started even in normal mode. I'm not a board repair technician, I'm just trying to fix this thing for fun, but I'm already at my wits' end. Do you have any idea what could be wrong with it? All voltages seem to be there, the machine should live, but it doesn't. Thank you very much for any help.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

No ideas? Is there a mistake in my post that nobody comments? Not enough/too much information? I'd like to fix this thing, but it cost me nothing and I'm not willing to put any money into it, so getting it fixed professionally is not an option. So if I can't fix it myself, in the trash it goes unfortunately.

[mon2]

Re: MacBook 2011 A1286 power cycle, no chime

What is the 820-xxxx number on your logic board?

What is the voltage to ground of PLT_RESET_L ?

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

820-2915-A. PLT_RESET_L is 3.35V.

[mon2]

Re: MacBook 2011 A1286 power cycle, no chime

What is the voltage to ground of PLT_RST_CPU_BUF_L ?

[reformatt]

Re: MacBook 2011 A1286 power cycle, no chime

https://www.cmizapper.com/products/t...gpukiller.html

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

PLT_RST_CPU_BUF_L is 1.05V

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

reformatt, this is way more than I'm willing to invest in this machine, I got it for free after all. Besides, would it even help me? It worked fine with just an NVRAM variable to switch to IGP, it started doing this after RAM upgrade.

[mon2]

Re: MacBook 2011 A1286 power cycle, no chime

There are many SMBUS interfaces / sensors onboard. It almost sounds like that the logic board is attempting to ping some device(s) and then eventually timing out

Measure the voltage to ground of each and every SMBUS SCL / SDA line to be sure they are not stuck. Each should be at the voltage applied by the local pull-up resistor as SMBUS is an open-drain specification.

Just a thought.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

Will give that a try and post my results.
Any idea why it doesn't start in SMC bypass mode at all? Fans just twitch once and then you can hear a ticking sound from the board, almost like short circuit protection kicking in.
Could it ba a problem that the GPU and VRAM have been physically removed from the board? But it worked in this state before...
Is there a way of doing NVRAM reset by shorting pads or something? Wanted to try NVRAM reset, but the machine doesn't respond to command option P R.

[dellxps15]

Re: MacBook 2011 A1286 power cycle, no chime

if 5v s4 goes up and down multiple times then it's bios problem, otherwise it some other component.

have here 2 same board with same syntom; one has visible big corrosion all over it and the other has multiple repair attempt. another one had manual gmux soldering and now poer on but no video.

firse check if 5v s4 come multiple times or just once. ( u need good multimeter to spot the spike).

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

dellxps15, do you mean PP5V_S4_P18V5S5? That's 0V. We might be onto something.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

Never mind, I had J5800 unplugged, after plugging it back in I get PP5V_S4_P18V5S5 and 18.5V boost just fine. It doesn't seem to be jumping, but I don't own a good multimeter, so no way to truly check I suppose.

[dellxps15]

Re: MacBook 2011 A1286 power cycle, no chime

p5vs3_vsw L7220 for spike.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

I don't see a spike. It just goes from 0 to 5V, then to 0V again when fans stop, 5V when fans start and this repeats. But like I said, not sure if my crappy multimeter could detect a spike. I have a slightly better multimeter at home, can try that on Monday.

[dellxps15]

Re: MacBook 2011 A1286 power cycle, no chime

some problem with cpu... volt on cpu is 1,15 , but drop to 0.75 ( around) after board power on correctly.

bios is ok and all pads are fine ? tried programming bios ( just in case) with a working one ?

probably board has bios string to bypass dedicated vga. with a pram maybe it start booting ( with black screen) and do chime, but after that u need to solve vga problem.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

CPU vcore stays at 1.15V even without memory, but does beep. Shouldn't that mean the CPU is ok?

BIOS chip area looks fine, no visible corrosion. I did not ty programming the BIOS, don't I need an image with cleared ME region and modified for my serial number? Sorry if this question is dumb, I've only ever flashed BIOS chips on PCs.

Yes, I wrote this into NVRAM nvram fa4ce28d-b62f-4c99-9cc3-6815686e30f9:gpu-power-prefs=%01%00%00%00. That's all I did as the GPU chip is removed from the board and it did work just fine after this, only after RAM upgrade it started with this issue, first starting after about 10 minutes, now doesn't start at all. Is writing this into NVRAM not enough? Could it boot (to a black screen, but I can VNC in) after NVRAM reset? But how do I reset NVRAM, it doesn't respond to command+option+P+R.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

Just did some continuity checks for good measure, all pins of the BIOS chip are connected where they should be.

[durchfall]

Re: MacBook 2011 A1286 power cycle, no chime

Tried flashing the BIOS, tried two different images I found online. It didn't help, the machine acts the same way it did before, so probably not a BIOS issue.
I kinda have a feeling the main symptom I should diagnose is no power in SMC bypass, just a small twitch from the fans, ticking sound from the board.