Mac mini 2018

[sauce]

Hi,

I am trying to help someone to repair a mac mini A1993 820-00939.
The mac mini won't power on.

Voltages on U7800 are all good except
PP1V2_PRIM 0v
PP1V_PRIM 0v

PP5V_G3S is missing too

Someone has the power on sequence of this ?

Thank you on advance.

Eric

[sauce]

Sorry forgot to give ohm values on missing voltages :

PP1V_PRIM => 44 ohm (quite low but I don't know if it's ok)
PP1V2_PRIM => 5.6k

PP5V_G3S => > 20k

[mon2]

Measure the voltage to ground of U7600 (PM_P5VG3S_EN), pin 24.

If this pin is not a logic '1' (high) then remove all power -> meter in resistance mode. Measure the resistance to ground of pin # 24.

Also measure the resistance to ground of L7650 (either side is ok) = PP5V_G3S. This is @ 20k ohms?

The 1v @ 44 ohms is likely ok since it is a low voltage rail. By design, low voltage rails are low in resistance. (As stated by Locutus / Star Trek - 'resistance is futile').

[sauce]

Ok thank you for your answer.

So PP5V_G3S must be present when we plug the power cable ?

[sauce]

So here are the results :

pin 24 => 0v so not enabled
resistance to ground very high => 7M

resistance to ground of L7650 => he says it starts from 0 but rises quickly to few Kohm (he's on Kohm range)

I ask him to measure U4901 on R4901 pads to see.

[sauce]

Hi,

Please someone to help me ? Data is quite important not for me but for the guy.

[mon2]

Do not frequent this leg of the forum often - usually camped on the laptop side.

Do replace the coin cell battery.

Can you share the history of this unit? Any liquid spill? Just stopped working one day?

Suggest to remove all power -> meter in resistance mode -> check the resistance to ground of each and every inductor on the board. The inductors are usually grey in color and have 2 legs on them. Each such inductor is linked to a local power supply which accepts the external high voltage of ~19 volts ( or whatever it is ) and brings it down to a lower safe voltage (acting like a buck regulator). If there is a short condition which is usually a defective capacitor due to age, the power supply leg will consume higher than normal current and the switching regulator will sense this and for safety - shut it down.

Again, with no power, meter in resistance mode -> one meter probe (either color is ok) to ground (metal shield is ok) -> other meter probe to an inductor of your choosing. Continue to review each and every inductor. Make a list of any suspects. Then that inductor must be compared against the schematics to understand if the resistance is normal (ie. low voltage rails will have a low resistance) or not.

PS: Ping me an alert once you are done the above and will review it asap.

[sauce]

Thank you.

The mac mini failed during use (the guy says overheat and strange smell) and no water damage.
The guy must send me the mac mini I known quite well laptops.

We already measure all coils but no short circuit to ground.

As I said PP1V_PRIM and PP1V2_PRIM are missing.

Do you know which voltages I must check in order ? I know laptops but not especially mac.

[mon2]

Ok, after some strong tea, here is my 2 bits (half a nibble) review on this case:

1) you are the 2nd poster with exactly the same fault so this is a common issue.

2) the PP1V_PRIM has a rather low resistance to ground so suspecting an indirect or partial short on this line but not a direct one which would be < 10 ohms. This places us in a pickle as we cannot really inject voltage and enough current to cause the shorted component to be identified. Prefer a harder short than 44 ohms to ground.

3) in reviewing the netnames, PP1V_PRIM is used to power the analog components of a number of required functions including: USB3 / PCIE2 / SATA2 / PCIE3.

Each of these are now suspects for the partial short condition that has caused this power rail of 6A to turn OFF.



4) Moreso, in the first post, you have observed that you are also missing: PP5V_G3S.

In tracing who is a consumer of this power rail? It is the USB interface.

Copied below is 1 port on the mac mini - there are others as well.

Suspects are:

PP5V_G3S_USBA
PP5V_G3S_USBC
PP3V3_G3S_WLANBT



5) Based on experience, the USB port load switches fail often. Given that a burning smell was observed, do inspect the board for burnt out components and especially the USB A / USB C regions of the board. The USB load switches are supposed to be like a multiple use electronic fuse but they often just fail by burning out. If true, they will tank the interfaces on the USB which will include the ANALOG USB PHY and power rail components. It will be best for you to review the board or at least clear and zoomed up pics of these regions of interest. My bet at this time is that the USB interface has raised this fault.

Do ask the owner if they were making use of the USB A interface. USB C interface?

PS: We repaired a 5K iMAC with a similar case for a client who took it to assorted shops and could not find the fault. In their case, the bulk cap at the USB load switch was shorted and causing an excessive current draw and tanked the entire operation of the logic board.

[sauce]

Awesome answer thank you.

I don't have PP5V_G3S because it is not enabled.

I don't have the mac mini yet but i will look closer that him because I have a good microscope.

[mon2]

The enable can be disabled after the host / master that creates this enable pin has gauged that there is a safety concern. That is the angle I believe that is a fault.

[Pragmatiko]

Hi,

I am trying to help someone to repair a mac mini A1993 820-00939.
The mac mini won't power on.

Voltages on U7800 are all good except
PP1V2_PRIM 0v
PP1V_PRIM 0v

PP5V_G3S is missing too

Someone has the power on sequence of this ?

Thank you on advance.

Eric

I have almost same problem. To mine PP5V_G3S is present.

[mon2]

Do review the voltage to ground of:

I2C_PWR_SCL
I2C_PWR_SDA

PPVBATT_G3_RTC_R



Post the measurements.


If the above are ok - then for both cases, attempt DFU with Sonoma. Can these boxes enter DFU ok?

See the DFU link and the positive feedback here:

https://www.badcaps.net/forum/troubl...-liquid-damage

* use the above thread to gain the feedback of a very similar fault

* use the following webpage to review the need for a DFU:

DFU Mode Restore (Macs) - LogiWiki

[sauce]

I finally have the mac mini !

I2C_PWR_SCL 1.8V
I2C_PWR_SDA 1.8V

PPVBATT_G3_RTC_R 2.92V

[sauce]

Just plugged mac mini on my hackintosh and it is in DFU mode.
Try revive without success (error 9)

[sauce]

Hi,

Unbelievable DFU revive with a real mac (I bought to repair it) worked !
The mac mini is alive.

So DFU and hackintosh even if device appears in DFU mode the revive does not work.

Thank you for everyone,