Q: error code 4sns/1/40000000:tcbh-127.902
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Mar 1, 2016 11:04 AMby loucarr,I purchased a new logic board on eBay and was planning on replacing it, but decided to first give the machine a real good cleaning first. And see if I found any obvious problems with the "B Heatsink" sensor. While taking it apart I found that it had 3 heat sinks and not just two towers like I had seen on YouTube. The third heat sink is a funny looking thing that I can only describe as having something of a sailboat design. It sits just underneath the ram cage and the cooling coils rise up and butt up against the two main heat sinks. I must have requested that configuration when I purchased the machine from Apple. I just don't remember. That threw me off for a little while but I pressed on and removed all three heat sinks. I then cleaned and re-applied the thermal paste to the processors and heat sink connections. The sensors all looked ok so I just made sure that all the sensor connections were firmly attached, put it all back together, and said a prayer.
Thankfully the machine is now working better than ever. I haven't run the apple hardware test because I misplaced the startup disk that runs it, but I believe the problem has been solved. As soon as I find the disk I will run it. Regardless I now have a smooth quiet machine again, that I believe still has a few years left. I can't thank you both enough for you help. You put me on the right track and ultimately helped me save the machine and a significant amount of money. The machine is now operating on a 500G Solid State Drive installed with a PCI Express card and could not be quieter. I think there is lesson here on not giving up on a computer that is still viable without first making an effort to fix it.
P.S. I decided to keep the extra logic board just in case.
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Mar 1, 2016 11:17 AMby Grant Bennet-Alder,That guy in the center of the board is likely the northbridge chip. That chip handles the signals into and out of the processor chips for I/O and RAM, so basically every important signal goes through it really fast, and it tends to be the hottest chip in the machine even when it is working properly.
Some Readers have reported really wonky behavior in the somewhat different 2009 model, if the black plastic pins that secure that heatsink firmly to the Nothbridge chip get old, brittle, and snap. That heatsink can become noticeably wobbly, and on dual chip models can be detected with the processor heatsinks still in place.
If you bought a spare board, I urge you to try it and make sure it really is a viable spare (although I have no reason to believe it is anything other than just fine).
