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Allow 10-15s once power is removed (charger & battery), before checking in diode mode, or ohm scale. https://boards.rossmanngroup.com/threads/how-to-collection.60974/

If external Caps Lock works, then you have USB activity. Can you confirm that on all ports? You should try again external video, when you have external keyboard working. Also check CPU core voltage (L7211) in that moment. BTW, keyboard still reacts after fans stopped?

First of all, welcome to the forum! Did you touch video connector without disconnecting charger and battery? Is your board 820-02020 model? Check diode mode to ground on JP600 lines and compare with good board, or reference table...

Did you still heard the chime when tested in Target Disk mode? Test if external keyboard works (Caps Lock light). Just in case, check if is detected in DFU mode.

Check R6970/1/2/6 resistors and their traces. If all good, remove R6934/5 and check L6960 voltage.

Check with Disk Utility...

Up to??? Anyway, post U6960 voltages.

Don't press power button, just press and hold T key. T2 machines turn on automatically pressing any key, or cliking trackpad.

I don't really understand what you mean. SSD encryption key is stored into CPU.

If Caps Lock reacts, board should be booted. Strange, because CPU core should drop to 0.65V when boots. Check if its SSD is detected in Target Disk mode.

Test external video closing the lid, once machine turns on. You can also test with internal LCD disconnected. If you get black screen, move the trackpad left/right and see if the cursor appears.

Probably not. If you have time to try, let as feedback. We don't have such information available.

https://openboarddata.org/?a=showboardsolutions&bpath=laptops/apple/820-02016

Disconnect power (including battery) and check in diode mode. Allow 15s second before checking.

First of all, welcome to the forum! You can't use new chip. Must get it from donor, together with its ROM. Only boardview available for this model. https://drive.google.com/file/d/1nEqjnW7ClcYCG6lCJokcQcOOItJi1i9Y/view?usp=sharing

Possibly low resistance to ground on some secondary power rail. Check them all (page 78). Also check page 40.

Do you get correct 3V3_G3H_RTC voltage?

What kind of swap? Just in case, check UR300 input signals; w/ and w/o JT201 connected.

First of all, welcome to the forum! Any fault history available? What is CPU core voltage (L7211) after 10-15s? Caps Lock LED reacts? Did you test external video?

"There was a short on c6961" What is actual voltage there? R6900 should be bad now...