Apple Mac Mini A1347 Late 2014 completely dead no power

[waakye]

Hello guys,
Thanks for all your supports. Really appreciate them.
I have a late 2014 mac mini that is completely dead. No power led no chime and does not boot when the power button is pressed.
I did all the PRAM reset and SMC reset an nothing just dead.
I took the back cover off and noticed that the fan spin slightly then stop and the cycle of the fan spin and stop continues.

Really hope someone can help me out again as this forum is the best out there.
Thanks in advance.

[mon2]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

https://youtu.be/7VltAzdVwqc

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Thanks! mon2

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Any help in fixing it?

[piernov]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

https://logi.wiki/index.php/A1347_20..._common_issues

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Thanks piernov. I will start from there and report back. I will have to locate the EFI chip first

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

I have tried to reflash the EFI and it still spins and stops then the cycle continue. I will try to get a clip of it maybe someone can chime in by seeing the video.

One thing I also notice that when I plug in a mouse in the USB port, the laser underneath the mouse flash every few seconds.

Thanks

[mon2]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Although too early to tell but most likely your issue is as documented by Louis Rossmann.

The issue is related to one of the switching regulators not being able to properly sense the voltage drop across the current sensing resistors. This is critical for the reasons mentioned in the video, to gauge how much current the voltage rail is sourcing / end load is sinking.

Let us say that the current sensing connection is broken on one leg. Respectively, the switching regulator can measure a voltage going into the current sensing resistor but does NOT see a valid voltage on the other side of this resistor. That is, zero volts due to the connection break (assuming this is the case). This translates to WAAAAY too much current being drawn by the target load / voltage rail - shut it down right away!! Often power supplies feature a retry (some latch but this is not practical for laptops to power down and up to reset the power supply) - this cycle of power on / quick off continues till the issue is fixed.

Review each voltage rail -> locate the power IC -> locate the current sense resistors and confirm the voltage is present on both sides. Also confirm that the voltage before and after the current sense resistor is reaching the switching regulator. The regulator must be able to measure the voltage drop to understand how much current is considered safe and respectively is dangerous to keep on.

Suspecting you have this case.

We have an a1466 with a similar pulsing action that needs some TLC to fix. So much corrosion and parts falling off as we brush but very similar issue. To be continued...

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Thanks mon2 for your help. Am a noob in this but am willing to learn if you can give me directions as where exactly the power IC is.

[dicky96]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

@waakye
This reply is not specific to this problem as I've never looked at any apple products but I hope they are much the same as anything else.

So a switching regulator (or buck converter) will involved a Power IC, and sometimes one or more Mosfets, and it will always involve an inductor. So the easiest way to find them is to look for the inductors. Once you spotted those, you can use your multimeter to find a nearby IC or Mosfet connected directly to the inductor. That will be the Power IC. You can then look up the datasheet for the part (or ask here if you can't find the datasheet or not sure what the part number is from the SMD code) and you can then find out if it actually is a switching regulator IC and which pins connect to the current sense resistor. Of course if it is a BGA type chip this is more difficult, but QFPN and other packages are usually easy enough to probe around. In general the controller IC will be QFPN, QFP, SOIC or SOT23-5/SOT23-6. Again I don't know what is common on Apple boards.

In any case the current sense resistor would usually be a very low value resistor directly in series between the inductor and the load.

I hope that helps though I am sure someone can tell you specifically what IC to look for on this board

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Thanks dicky96. I will disassemble the mini later. I am now back to reality aka work.
I really appreciate your help on this.

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Hi, I finally got the mac mini open up. I really have no idea where to begin from. Does anyone has a schematic of the logic board to share. It's a 2014 mac mini.
I have attached the logic board photo below.
Thanks

[dicky96]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Well, these are the inductors (see pic) - each one will be generating a power rail. Near each one will be the power IC that drives it. Also by the inductors and power IC you should find capacitors on both sides - one will be for the input voltage rail and the other for the output voltage rail
I know nothing about Apples, but if this was some unknown dead board I was trying to fix, I would also check the input voltage (from the power adapter).

I would then check the voltage on each of those inductors to see if power rails are present. If there is no output power rail (on the inductor) I would try to determine if the input voltage rail is present near each power IC (check on the electrolytic/polymer/tantalum capacitors).

I would also be looking for datasheets for the power ICs as that usually has an example circuit, but at the very least would tell me which pin has the input voltage rail.

Have a look, and mark the voltages on the image then re-post it



So there are some ideas for you to start

best regards

[dicky96]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Here you go, this picture probably explains better what I mean. This is from a visual glance of your pic of the board only, so you need to measure voltages to be sure I am right. But this is what I see when I look at it.

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Hello dicky96,
Thanks for your help. I really appreciate you taking the time off your day and helping me out. I was able to take some measurements at the points that you marked on the picture. I have updated the picture with my findings.
I looks that I am getting 11.88VDC on the inputs voltages at all the points you marked IN. Unfortunately, the OUTPUTS are not that good. sometime I see the output measures 02.1mv and goes to 1.485v and goes back to 02.1mv. As they say a picture is worth a thousand words.
I have attached the picture.

Thanks again for your help.

[dicky96]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

No worries mate

So it looks like you have 12V going in and 3.3V but nothing else - most likely that 3.3V is the standby voltage supply, and your board is not powering up

The one that is going to 1.485V then back to zero, near as damn it, that sounds like it is repeatedly trying to power up then shutting down again.

Bear in mind some of the points I marked as OUT could be the ground end of the capacitors. Measurethe voltageat the inductors to be sure (if you didn't do that already.

Power off and check the resistance from each of the coils to ground. Are any of them reading zero ohms? In which case you have a short on that voltage rail stopping the board from powering on.


Hopefully someone with knowledge of Apple products will come along with more specific advice, I'm just trying to tackle this from a basic electronics standpoint

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Hi dicky96, thanks for replying.
I took some measurements of the Coils with power applied and also the resistance of the Coils without the power applied and below are my findings:
I have attached pictures with notes on the resistance measurements of the coils and also with the voltages on the Coils points.
Seems that the coil that was reading 3.32 vdc is also the coil that is reading open on the resistance.
Please see the pictures with the notes.

Thanks

[dicky96]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Well for sure an inductor should not be reading open circuit, but seeing as you have 3.3V on that one I can't see how it could be open circuit as that buck regulator appears to be working.

If it really is open circuit then there is your problem to start with. You need to fix that first.

You have no short circuit to ground on any of the power rails so it appears the board is not powering up (stuck in standby) or you do have a problem with that inductor.... but that seems illogical to me.

[waakye]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

When I measure the resistance on that inductor that reads 3.32vdc when power is applied,( I disconnected the power prior to measuring the resistance). I see that it goes to 2.0Mohm and slowly keeps dropping then the multimeter read open and reads another value n keep cycling.
Hopefully there is a schematic of the logic board somewhere or someone can chime in.
Thanks again dicky96. I am learning a lot from you.

[dicky96]

Re: Apple Mac Mini A1347 Late 2014 completely dead no power

Something is wrong there. You are measuring the resistance with the power turned off, yes? Also there is no voltage measured on that inductor to ground (like would happen if you have some capacitors holding a charge)