HOW TO collection


Staff member
I hope this "How to" collection will help our members.
I will possibly modify this post in time, if updates available.

It reffers to simulate power button function, when the keyboard is not connected.
We need to do this when we work with the board alone on the desk, or when we have doubts about power button.
Apple placed special pads for this purpose; as example, R5015/16 (3115), R5115/16 (00165), R5225/26 (00923), depending by model.
Newer models have some kind of switch pads (not populated), marked as RE030/31 (00850), or SWE10 (01521), etc.
Just search in pdf for "ONOFF"; easy to find them, connected to SMC_ONOFF_L, or PMU_ONOFF_L.
In fact, we don't really need to use these pads exactly.
Is very easy to solder a tiny wire on the pad corresponding to the signal; just touch any metal plate with it, when you want to simulate power button.
Just a temporar contact, of course.
When I really need to use it many times, I prefer to solder a small button, with 5-10cm wires.

Check PCH's RTC signals:
We reffer to DC signals, not 32KHz, or other PCH clock signal.
Intel platforms have 4 typical signals, RTC_RESET_L, PCH_SRTCRST_L, PCH_INTRUDER_L and PCH_INTVRMEN.
Newer platforms, may not use PCH_INTVRMEN or/and PCH_INTRUDER_L.

Start in SMC bypass mode:
- MacBook
Press power button, maintain it pressed, connect charger and release the power button after 5-10s, or when the fan starts.
- iMac, Mac Mini
Press and hold power button.
Insert power cord (previously removed) and release power button after 5-10s.
Then press power button again (shortly).
Fan will start with max speed, if succeed.
Used to discard SMC sensor problems.

Start in safe mode:
Press Shift key and power button at same time.
Can help to diagnose if a problem is being caused by software that loads on boot.

Start the built in AHT:
Press D key and power button.
Very useful for the machines from 2015 and newer, as no ASD available since then.

Start from built in recovery mode:
Press Command + R keys and power button.

Start in target disk mode:
Press T key and power button.

Start in single user mode:
Press Command + S keys and power button.
Allows you to run terminal commands with full access to the file system.

Test in diode mode:
Connect positive probe of the multimeter (red) to ground and touch the test point with black probe.
Sometime (rarely) we need to test in reverse direction.

Inject voltage to find a short:
Many times we face with short (or very low resistance) to ground in a power rail.
Be aware, some CPU/GPUs have very low value as normal; latest CPUs measure like pure short in fact!
The fastest and easiest way, is the voltage injection method.
Be sure first is safe to inject voltage there; read the forum, if you are not sure!
Always start with low voltage (like 1V), and slowly increase (if needed), no more than 120% of nominal voltage of that power rail.
We need powerfull lab PSU for this purpose; because sometime, we need to inject more than 10A, with low voltage as 1V.
I recommend analog settings, as being easy to manipulate.{"sku_id":"12000023035634267"}{"sku_id":"20000000188269000"}
These are just examples, search on Internet and choose which one you like.
BTW, adjusting output current is not a need.

Enter DFU mode, for T2 machines:
Many people complain they can't acces DFU mode following Apple instructions.
Here is a link with detailed steps, reported as working.

Check USB activity:
The best and safest way (not cheap)
The cheaper way, using an USB pendrive with Link LED, like this (just as example)
I use 64GB with preinstalled macOS El Capitan, or 32GB with ASD (12 versions).

Disable GPU on some MacBooks Pro:
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