Remove R9704. The first wire connects to BKL_PWM (the top pin of where R9704 was).
The second wire connects to WS_KBD23 (pin 48 on U5701 or pin 6 on J5713). In the above picture it is the 6th pin from the right on the top edge
The hole in the Tiresias fits snugly over the ROM chip. Solder all 8 connections from the Tiresias to the side of the ROM chip. Do not let too much solder flow down between the motherboard and the bottom of the Tiresias as that could cause a short circuit. In case you are not sure check for shorts between the adjacent pins on the ROM, there should not be any!
The Tiresias GPUkiller mounted over the ROM on the 820-2915.
The Tiresias GPUkiller for the 820-2915.
The position of R8911 which you have to remove on the 820-2915.
Do not skip this step! One resistor has to be removed from the motherboard.
R8911 has to be removed to turn off the external AMD GPU.
This resistor has to be removed because the OS tries to talk to the GPU during boot. If it sees the GPU it might try to use it. And if it tries to speak to the GPU and the GPU gives strange answers (remember that it is dead...) then the Mac might crash when booting.
If you want the Tiresias to handle the LCD backlight then you have to solder two wires from the Tiresias to the motherboard.
When installing the wires it is important that you also remove R9704.
The first wire (green in our pictures) connects to the PWM pad on the Tiresias. The other end connects to BKL_PWM. Connect onto the top pad of R9704. R9704 has to be removed.
The Yellow wire (WS_KBD23) can either be soldered onto pin 6 of the keyboard connector J5713 or onto pin 48 (6th from the right) of the keyboard controller U5701. Soldering onto U5701 is easier as the keyboard connector is very fragile and liable to melt.
When you run any OS before High Sierra then this modification is not needed but there is no problem if you do implement it.
When you run High Sierra (or later...) then you have to do this modification. If not you can not controll the brightness, and worse, the brightness will disappear altogether after system sleep.
Feel free to try the Mac after doing step 1 and 2 and BEFORE doing step 3. The Mac should go 'boing', give an image, and boot.