Does not power on after SMC reset, will on SMC bypass.

Alright, bear with me here because I am by no means an expert and there is a long story. This computer was running perfectly up until about a year ago when I dropped it. After doing so, the hard drive would not boot and the screen cracked. I took it to the Apple Store and they basically said that I was SOL and that I should just buy a new computer. Since I already had an iMac, I just decided that it was good enough for what I needed to accomplish.

Recently, however, I remembered (go figure) that I know how to work on computers and decided to get a bit adventurous. I bought a new LCD display and HD for the computer and replaced them both, along with a new keyboard. After reassembling the computer, it would not respond by pressing the I/O button; no flashing lights, no whirring fans, nothing. After a little digging on the internet, I came across a description on how to start up a MBP that seemed dead by unplugging the laptop, holding the power button for 10 secs, plugging the computer back in while holding the power button for an additional 10 secs and then releasing and pressing it again to get it to boot. This worked beautifully and I was able to install OS X onto the computer.

The problem with this, however, was that the fans were running at max, the keyboard backlight was not working, the computer seemed to be running a little slower than desired, and the magsafe LED wasn't responding to the battery's current charge state. Since I assumed the battery to be dead after sitting around for the better part of a year, I figured the last part to be of little issue. I later found out that what I was doing was bypassing the SMC which explained quite a bit. I then tried to reset the PRAM and the SMC (in that order) and the computer would again not turn on. It seemed that every time I tried to do an SMC reset, the computer would not turn on.

Frustrated, I took the MBP to the apple store and the genius there ran a hardware test to find that my CPU 0 Die Analog and Right Fin Stack Proximity sensors failed the hardware test. He told me that either there were loose cables or the logic board was bad. I decided not to give up and went home and took the computer back apart and carefully examined the cables and the logic board itself. The board looks to be in great shape (aside from a little dust), but I did notice that my left thermal sensor was not seated properly and that my right thermal sensor had a tiny piece chipped off the side of the seat. They both, however, seemed to seat firmly in place once I put it back together. After reassembly, I tried a reboot and still had to bypass the SMC to get it to start. Also, iStat is saying that both fans are at 0 RPM, which can't be true because of their attempt to imitate a Hoover vacuum, and that the left and right sensors are reading 32F.

At this point, I'm getting a little antsy because I feel like I'm almost there but I'm not sure of what other steps I can take. I did stumble across something stating that the MBP will not start up properly if you are using a 60W magsafe, which is what I have. I was gonna try to order an 85W from ebay and see if that helps. Also, at the Apple Store, the guy put in a working battery and the computer seemed to recognize the battery which it is not doing with my current battery.

Any help would be greatly appreciated! Thanks ahead of time!


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I would like to add that I tried to update the computer to Mountain Lion to see if that would help with the issues, but that caused the screen backlight to turn off once the OS booted up. When I went back to Snow Leopard, though, the screen backlight works 100%.


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The fans running at max are default safety settings from the EFI when your sensors don't report, or report outside "acceptable" limits. They will contintue to run at max until you fix the problem (sensor, cable or board).

Fans running at max will slow the machine. An overheating CPU can slow the machine.

If the sensors are on the logic board you'll have to replace the logic board (component replacement is a very advanced DIY project) , or find an electronics shop that could do it... compare the cost of repairing vs replacing.

Your dead battery could be part of the power on problem - try booting with only the power supply plugged in.

If this Answer is helpful please remember to return and mark it Accepted.

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First, any laptop definitely should use the proper wattage adapter. Look up what yours needs in Mactracker, a free and terrifically useful Mac specs database app found at

You didn't mention which model MBPro you have but it looks like the one I have—an early 2008 "pre-unibody" that had a similar problem you mention. However I didn't drop it, it just froze in the middle of a paying job, with the screen going to all saturated colors. It was running cool, fans were normal speed. After that I couldn't get it to even boot. The local Apple tech ran a diagnostics on it, said there were a few problems: graphics unit was malfunctioning, power problem, and a couple sensors were not working. This model had such a bad history that Apple gave free fixes to the motherboard issues for 3 years from purchase even without AppleCare. But that doesn't help when it fries after 5 years.

I had been using this computer for a long time on my desk only and had removed the battery (partly charged, excellent condition with less than 30 recharges) to preserve it from needless heat and topping up cycles. It was not in the computer when the big freeze hit. I tried putting the battery in but it made no difference, and showed no charging happening either.

Now back at the Apple store, I mentioned this to the technician who said that the battery was shot and I asked how that can be. He put in another battery and LO, and Behold! the computer started up!

Why it wouldn't start up without any battery in it but WOULD start with a recognizable battery is still an enigma to me, and may be solved by the SMC reset which I haven't tried yet, but the graphics problem seemed an insurmountable problem that the technician said could only get worse.

The problem with the graphics chip shows up as several rows of pixels not working on the left side. All this happened last December. Just yesterday I found an independent technician in UK who advertises resoldering MBPro graphics chips which he says is quite straightforward. The connectors just fail to connect perfectly through hot use or just poor assembly after some time in certain models, like mine. The price of resoldering seems reasonable, if that's all that is needed.

However, the technician said the other issues the Apple tech found—sensors not working, power problem—are a whole 'nother bunch of issues to deal with and he honestly said it could end up costing more to try to find and fix everything than just getting another logic board, or another computer, since the logic board was about the price this model fetches as a functioning computer on eBay.

So a compound situation is not an easy or cheap fix. You probably could try replacing the sensors but if the CPU 0 Die Analog is also a problem, find a real geeky technician to estimate a repair. It may be time to just get another logic board.

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The reason a shot or dead battery couldn't boot your box is that some newer models now will not boot without a battery holding approx 12% charge. As to what cause a shot/dead laptop battery it's not just the electrolyte but a program on the board inside the case. Computers are getting more and more "aware" as time passes. There are many logic sub-routines that all must report to the EFI before POST passes.


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Had the same problem twice: Macbbok Pro died without warning while surfing on battery, and did not start at all any more. Only the above mentioned SMC bypass helped as a temporary fix. Problem that fans are on high speed, battery not recognized nor charging, and sleep doesn't work anymore, since the SMC is bypassed during startup and controller does not get any infos on battery, temperature and the like. Doing an SMC reset afterwards put the laptop again in dead mode.

I got around with ordering a new "Left I/O board" or "DC-In board", installed it and voila: everything's fine.

One month later computer died again with same issue and the same process: surfing the web on battery. Go figure. Ordering the next I/O board from ebay, installed it, but did not work this time. Afraid that I ordered a broken one. Again got stucked with the SMC bypass option.

I did read about the 85W power supply, but negleted it since I was sure to have the correct one. I have 3 Macbooks around in the house, and replaced a lot of power supplies during the years, so I was sure to have a good and right one connected. I just checked one other power supply without checking the label, didn't work. It could also not imagine what the power supply could have to do with it.

To make it short: one computer had a 85W supply, which I connected to the broken one, and indeed it fixed the issue!

Question remains why did the macbook running on a 60W supply for years without issue. Something must have been broken in between.

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Because you still had charge on the battery everytime it did boot before. Your battery was either too low when your problem started or bad. You can use a 45 watt charger with the battery but it will get very hot. You can also also use the 45w and 60w charger with little bit on the battery and unplug the battery and it will run alone off the charger. BTW that is not a Bypass it's a Debugging mode for SMC, it just seems like it's bypassing it that was the name given for it when first discovered.


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