Can you confirm that this processor is always behaving this way or just when idol? I would assume that if the board has been replaced and tested by more than one shop, then there is probably nothing wrong. Processors have power management states that can reduce the processor speed to low values, this is used with products like the Mac book* in order to save energy.
Thanks for your reply. I realize I should have been more specific.
The CPU seems locked to 800 Mhz under any load I can throw at it. I have tried typical benchmark tools such as geekbench 3 as well as my own code and the frequency never rises above 800 Mhz. Geekbench scores are 1/3 of what they should be and the temperature never rises above 60 degree C.
I understand that the processor has the ability to adjust its clock freuency in response to external factors such as temperature and available power and that some of that happens at the OS kernel level, some at the firmware level and some at the chipset level? I'm no expert in this so it's difficult fo rme to debug. Since the issue is the same on Windows and linux I exspect its not the OS.
The issue begain in combination with changing the logic board and a broken battery. I know that underclocking is a thing typically related to broken batteries in MBPs, so I wonder if it somehow got stuck in the low frequency state even after changing the battery.
Apple has requested that all questions regarding Apple systems and software be addressed directly with Apple support. I recommend checking the link below for troubleshooting assistance on your Apple computer: