820-3115, Odd Power/Sleep Issues

SMMRepair

Member
Working on another 3115 with some tricky behavior. We have about 100 3115 boards in the queue, so I'll probably be posting a few per week for a while. 90% of them I can diagnose and repair, but some are particularly difficult...

This particular board has symptoms that I'm afraid may be related to the PCH, but we'll see:

1. No liquid damage; board is a clean pull from a unit that would not reliably boot. Original owner said it would "cut off" when it got to OSX sometimes, but we haven't noticed that.
2. Unit powers on consistently, but does not boot consistently; most of the time, the board will power on and make it into OSX. Sometimes, the front LED will dim to 50%, stay on, and nothing happens. It seems to have issues booting more often when a battery is installed, but it will have issues sometimes without a battery installed.
3. Board will boot 100% of the time, without issue, if booted in SMC Bypass mode.
4. Has trouble when trying to reset PRAM about 50% of the time; it will restart once, but hang. If I let the keys go, it stays hanging. Never boots. This behavior occurs roughly 20% of the time when resetting the PRAM.
5. If the unit does make it to OSX, it will not wake from sleep upon opening the lid once it has been to sleep. When the lid is closed, the front LED behaves normally--stays on for 10-20 seconds, then pulses. When lid is opened, front LED turns off, but no video (backlight or image data); if I close the lid again, it will "resume" sleeping, BUT the front LED never pulses--it simply stays at full brightness.
6. Passes ASD without any issues.

I was thinking it may be an SMC issue, since the symptoms "worsen" when a battery is installed, and since it works fine every time when booting in SMC bypass mode, but I honestly don't know where to start or what to check for this issue. Board was tested in known-good assembly, with known-good BIL, etc. No liquid. No damage or missing components. All main rails are normal and without any detectable shorts.

I replaced the BIOS chip from another board just to see if it booted more reliably, but there was no change.

Any ideas? I wanted to post before blindly replacing the SMC.
 
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jgraffis

New member
booting into os issue could be the hdd cable. I've change a ton of these but sounds like theres more issues that or bigger issues than that.
 

SMMRepair

Member
Thanks! Yeah, we've tested the board in 3 different known-good test cases. Cable should be fine, so I think there's something else going on. Thank you!
 

dukefawks

Administrator
If you have 100 more of these the first thing you should do with this board is toss it in the garbage. Do a quick check without RAM. If the beep is also not consistent then this is a waste of time. If it consistently beeps it could be a bad RAM slot.
 

SMMRepair

Member
Thanks, Duke. Yeah, we've had to just consider some boards for parts. Most I can fix, and most of the ones I can't fix I send to a friend who is way, way, way more skilled who can usually fix them. I'm trying to get better at diagnosing specific issues for my own memory bank, so I appreciate it. I'm going to consider this one as one of those. Thanks!
 
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