Update: PROBLEM SOLVED.
I post here for the sake of future googlers, as I appear to be the only guy on the internet who wanted to dig more into this problem and changing the backplane just seems to push back the issue: THE PROBLEM ARE THE CAPACITORS.
I tackled the task desoldering all the board capacitors, specifically:
I managed to desolder all of these 11 bad boys, 8 of which are SMD ones --> desoldering them is kind of a challenge and breaking the traces is very easy. And I mean very
very
easy. Luckily I just stripped off 2 out of 16 total traces, which is a good % given that I'm almost a newbie in microsoldering. With the help of some new copper traces, using those super tiny shiny copper points I was blessed to have, I rebuilt the traces as good as I could and changed all of the capacitors, even if I apparently didn't find any issue while testing those I removed.
My guess btw is that the issue is related to the biggest ones, as one of them literally blew up during my first test after reassembling the computer, probably due to the new traces not being reliable as I thought they would be.
Disassembled again, changed the exploded capacitor with more attention to the damaged trace, reassembled the Mac and it turned itself on as I inserted the power plug (no GPU was installed during these first tests).
Point is, the issue finally became replicable, as the Mac refused to turn on with the power button but turned itself on 100% of the times when the plug was removed and put back again. My guess is about the missing CMOS battery (I didn't have a new one around) not allowing me to use the power button.
So yesterday I got a new battery and put it on, and after some testing, a NVRAM reset (which involved some kind of rage as the problem seemed to be there again after the NVRAM was resetted - pure nonsense) and a RTC reset with the dedicated button, the Mac looks like it's fixed.
It's all working, the power button responds when it should and leaving the Mac turned off but plugged in overnight made me turn it on this morning without any issue. I also changed the GPU I was using, took off the plug just to move the computer from its location, etc so normal use, and it 100% turned on with the power button normally.
I'll keep you updated in the next weeks as I'm planning to put an SSD and installing some new software, all of it involving turning it on and off.
I post here for the sake of future googlers, as I appear to be the only guy on the internet who wanted to dig more into this problem and changing the backplane just seems to push back the issue: THE PROBLEM ARE THE CAPACITORS.
I tackled the task desoldering all the board capacitors, specifically:
I managed to desolder all of these 11 bad boys, 8 of which are SMD ones --> desoldering them is kind of a challenge and breaking the traces is very easy. And I mean very
very
easy. Luckily I just stripped off 2 out of 16 total traces, which is a good % given that I'm almost a newbie in microsoldering. With the help of some new copper traces, using those super tiny shiny copper points I was blessed to have, I rebuilt the traces as good as I could and changed all of the capacitors, even if I apparently didn't find any issue while testing those I removed.
My guess btw is that the issue is related to the biggest ones, as one of them literally blew up during my first test after reassembling the computer, probably due to the new traces not being reliable as I thought they would be.
Disassembled again, changed the exploded capacitor with more attention to the damaged trace, reassembled the Mac and it turned itself on as I inserted the power plug (no GPU was installed during these first tests).
Point is, the issue finally became replicable, as the Mac refused to turn on with the power button but turned itself on 100% of the times when the plug was removed and put back again. My guess is about the missing CMOS battery (I didn't have a new one around) not allowing me to use the power button.
So yesterday I got a new battery and put it on, and after some testing, a NVRAM reset (which involved some kind of rage as the problem seemed to be there again after the NVRAM was resetted - pure nonsense) and a RTC reset with the dedicated button, the Mac looks like it's fixed.
It's all working, the power button responds when it should and leaving the Mac turned off but plugged in overnight made me turn it on this morning without any issue. I also changed the GPU I was using, took off the plug just to move the computer from its location, etc so normal use, and it 100% turned on with the power button normally.
I'll keep you updated in the next weeks as I'm planning to put an SSD and installing some new software, all of it involving turning it on and off.
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