Apple Mac Mini A1347 Late 2014 completely dead no power

[waakye]

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

I will try and measure the resistance of that inductor again just to be sure.
Thank

[waakye]

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

So I kept the multimeter on the suspected inductor for about 2 minutes and I saw that the resistance reads 3.6k ohms on each side of the pins.
Now am super confused.
Any help guys

[dicky96]

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

An inductor like that should read short circuit on a multi meter, more or less.

[waakye]

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

Do you think that inductor might be the culprit?

[dicky96]

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

I can't quite understand it. Yes an open circuit inductor is obviously a fault, but then that same power rail has 3.3V which suggests that this buck converter is working which would mean the inductor is working - unless that 3.3V got there by some other route

[waakye]

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

I will probe the inductor again for more information. Thanks again dicky96.
Really appreciate it

[waakye]

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

Does anyone by any chance has a schematic of 2014 mac mini A1347 that they want to share.
Thanks

[dicky96]

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

Does anyone by any chance has a schematic of 2014 mac mini A1347 that they want to share.
Thanks

Ask in the desktop schematics requests section, you are more likely to get a response there
https://www.badcaps.net/forum/forumdisplay.php?f=15

[waakye]

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

Thanks.
I asked the forum for the schematic.

[waakye]

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

No mac mini schematic available in the desktop schematic section. I will try and measure the resistance and voltages on the inductor pins again.

[waakye]

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

I am open to any ideas. I know there are many knowledgeable individuals here. dicky96 really help me a lot. Guided me on the right track. I am still reading the pulsing voltages on all the other inductors except the one with the 3.32 volts.

[dicky96]

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

I am still reading the pulsing voltages on all the other inductors except the one with the 3.32 volts.

I thought you said the supply rail that was going to 1.45V was pulsing on and off, but all the others were reading just a few mV? Apart from 3.3V which I think we can assume is the Standby Voltage rail

[waakye]

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

My bad. The voltage is 00.2mv then it goes to OL and then to 00.2mv and keep pulsing between those two values. On some i am getting 22.5mv and OL and keep cycling between those two values.
I was probably reading those wrong. Sorry bout that

[dicky96]

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

No, probably you are reading them right but your multimeter can't read the voltage fast enough because it is auto-ranging

If it has a non-auto voltage range like 19.99VDC then select that. Now can you see what is happening. Possibly it autoranges to 1.99V by default and all the other voltage rails are higher than that so you don't get to see what is happening

Having said all that it looks like this board is stuck in a constant power on - power off cycle (apart from 3.3V standby) and as none of the voltage rails appear to be short to ground it is not obvious why. Possibly one of the buck regulators (those inductor circuits) has a faulty high value, or open circuit, current sensor resistor so it keeps thinking here is an over current situation and shutting everything down

This is where things get more difficult, but not impossible. Next thing, we need to identify the Power IC's (what are the part numbers) for each buck regulator and see if we can find a datasheet for each one

So that's the next thing you need to do. Read the IC part numbers then google for 'datasheet xxxx' where xxxx is the part number. If that does not work ask to identify the IC or for datasheets on the forum.

[waakye]

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

Thanks for your reply. What are the power IC and where are they located? I will look for the datasheet if I can identify the power IC. Is it the ones I circled red in the photo below

[dicky96]

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

Those are capacitors. Let's just go back to that open circuit inductor again first. Regardless of how the 3.3V is getting on to that supply rail, you should not have an open circuit inductor. If it is actually open circuit, which your multimeter says it is (then the 3.3V is getting there by some other route) so you would see 3.3V on one side of the inductor and something else (probably 0V) on the other side. Is that what you have?

Under that black insulating plastic on the bottom right hand side of the board, is that a CMOS battery? If so, what voltage does it have?

[waakye]

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

Yes. I am getting 3.32vdc on the other side of the inductor.
Yes the CMOS battery is on the bottom right hand side of the board and it measures 3.09vdc.
Note: I removed the CMOS battery and power the board and am still reading 3.32vdc on that inductor on both sides.

[dicky96]

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

I'm sorry to say I am totally at a loss to explain why that inductor reads open circuit when it has 3.3V both sides

Can anyone one else suggest how that could happen?

[waakye]

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

thanks for helping me understand the circuit a little more. you really improve my knowledge . i really appreciate your help. It is weird that there are no schematic for this board 820-5509 anywhere. I guess that is Apple for you.
Hopefully someone here can also chime.

[waakye]

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

Guys any help on this?