Power throttling issue on MacBook Pro 2012

Hello,

I have an issue with my Mid-2012 Macbook Pro (non-Retina). A1286 I think. 9,1.

The computer is pretty beaten-up, but it still works. Recently, I noticed some heavy performance throttling when the computer needs to draw a lot of power - e.g. playing games which use GPU intensively.

Here are the facts:

1. I am using an 85W original Apple charger which was purchased around 3-4 years ago, after the old one broke down due to classic cable issue. I think the cable might have shorted back then (which is how I noticed it), but this was 6+ years ago.

2. The battery is not original, purchased relatively recently and is made by a company called EGOWAY.

3. The battery is working properly. It is at 14 cycles, the computer works for hours on battery without any issues. It can be emptied and fully charged properly.

4. The issue is _not_ related to thermal throttling of CPU and GPU. The issue happens when CPU and GPU temperature is below or around 60C. Thermal throttling for this model happens around 90C+, I have experienced it before when the fans were clogged. Regardless, the fans are completely clean and the pathways for airflow are completely open at the moment. The fans are running at an aggressive curve where they reach 100% at 65C using MacsFanControl. (6200 RPM both at maximum)

5. The issue manifests itself in a few seconds after computer power draw increases. The CPU clock frequency is quickly reduced to 1.2 GHz and GPU clock frequency is reduced to 270 MHz from 775 MHz.

6. The issue _only_ happens when the charger is connected to the computer. As soon as the computer starts drawing around 30W+ from the charger (according to iStats "DC In"), the throttling happens and the power draw sharply drops. This happens regardless of battery charge status. If I run the intensive applications without charger being connected, the computer is able to draw around 90W from the battery without any issues. The performance is at nominal levels on battery.

7. The issue is _below_ operating system level. Happens both on OS X and Windows 10 Bootcamp with the same throttling signature.

8. I have done the SMC and PRAM resets while trying to fix this issue. I don't have a working internal keyboard attached to the computer, so I have done the reset by using rEFIt and correct SMC files downloaded from Apple website. I know that the process completed successfully because the fan speeds have returned to normal before the tool rebooted the computer.

9. Apple System Diagnostic tool that runs by holding Option+D gave no errors. I had done this before the SMC reset.

10. The keyboard stopped working 3-4 years ago from very minor water damage, but was not an original keyboard anyway. I was cleaning the keyboard with a damp paper towel, somehow a water droplet must have gotten in. The paper towel was not dripping wet, it was damp. I couldn't believe it when it stopped working. I have been using the computer with an external keyboard since, with back-panel removed and lid shut, so that the fans can get enough air. There might be potential water damage somewhere. Perhaps it is not the keyboard that is broken? When the internal keyboard is connected to the board, it sometimes prints random letters. But it's mainly non-functional and therefore disconnected.

11. There is a long-standing issue with the computer where computer does not recognize the charger (e.g. no green light) if it is disconnected from the computer and reconnected. The charger is only recognized if I disconnect the battery and the charger when the computer is off, connect the charger (which turns the computer on) and then reconnect the battery.

12. I have noticed the throttling issue a few days ago. Might have been happening for 2~ weeks.

Based on what I have read, it seems the chip designated as U7000, its peripherals or the SMC chip might be broken somehow? I do not think I can find somebody trustworthy that can perform board repairs where I live (middle east). I have minor electronics skill, but I think replacing a such a small chip on the board is beyond my abilities. What would you suggest?

I have TG Pro and iStat trial versions installed if you need any extra information.

Thank you very much for reading.

Edit: coconutBattery while charging without load:

While charging with throttling:

Full charge while throttling: