Mac mini 2018

[Pragmatiko]

Hi all, did you solved? I have same identical problem but I have PP5V_G3S 5V

PP1V_PRIM 0V
PP1V2_PRIM 0V

led of Mac Mini is blinking

[mon2]

Pragmatiko - with no power , measure the resistance (not diode mode) to ground of PP1V_PRIM and the PP1V2_PRIM rails. Post your measurements.

[Pragmatiko]

Hello,
on PP1V_PRIM 46ohm, and PP1V2_PRIM 5Kohm

Tks

[mon2]

What is the history of your unit? Just stopped working one day? Any liquid damage? This model appears to be plagued with the same fault.

PP1V_PRIM @ 46 ohms, to me, sounds too low for a normal logic board. This rail is also used to power the USB PHY.

Carefully, measure the voltage to ground of:

PMU_P5V_USBC_ISENSE
PMU_P5V_USBA_ISENSE

PP5V_G3S_USBA
PP5V_G3S_USBC
PP3V3_G3S_WLANBT
PP3V3_G3H_ENET

[Pragmatiko]

no liquid damage. I got it from a friend that says the unit stop to working. Now when i plug it i can see only led to blinking. i will che the voltage you suggested me and reply to you soon.

[Pragmatiko]

What is the history of your unit? Just stopped working one day? Any liquid damage? This model appears to be plagued with the same fault.

PP1V_PRIM @ 46 ohms, to me, sounds too low for a normal logic board. This rail is also used to power the USB PHY.

Carefully, measure the voltage to ground of:

PMU_P5V_USBC_ISENSE voltage not present
PMU_P5V_USBA_ISENSE voltage not present

PP5V_G3S_USBA voltage present 5V
PP5V_G3S_USBC voltage present 5V
PP3V3_G3S_WLANBT voltage present 3,3V
PP3V3_G3H_ENET voltege present 3,3V

please read above

[Pragmatiko]

update, i have removed L7821 and L7822 and now voltage side IC is present. Then i suppose that 44ohm resistance downstream coil is not good.

[mon2]

Can you clarify? There is still a FB connection resistor @ R7820. Carefully remove it. Do not power up without these components. Great that you are comfortable with this process as the parts are incredibly small. There is also a cluster of pins on U7800 that directly bond to this rail (R12, T12, etc.) - so U7800 is still a suspect.


Then confirm which side of this rail is shorted? Is it the producer (U7800) or consumer side. In your post, do share the pin # of the removed coil(s) that show the 44 ohms to ground.

One tool that would help here and we are considering it to source soon is a low ESR capacitance meter that can measure in milli-ohms. With such a tool, it should be possible to test each cap or whatever on the board to confirm if it is shorted or not. There is a sea of parts onboard to investigate.

[Pragmatiko]

Well,I removed R7820 too and still I have low resistance consumer side. There are a lot of capacitor on that PP1V_PRIM. I will try to test with ESR meter (tomorrow maybe). Thank you for your support.

[mon2]

There is also a cluster of pins on U7800 that directly bond to this rail (R12, T12, etc.) - so U7800 is still a suspect.

Really interested to hear of your test results with the ESR meter. It is on my wish list. There is an excellent YT video on this topic and it is a no brainer to justify the purchase. Just scouting for a good quality one at a fair price.

[Pragmatiko]

There is also a cluster of pins on U7800 that directly bond to this rail (R12, T12, etc.) - so U7800 is still a suspect.

Really interested to hear of your test results with the ESR meter. It is on my wish list. There is an excellent YT video on this topic and it is a no brainer to justify the purchase. Just scouting for a good quality one at a fair price.

I don't know why, but I strongly believe that the problem is on R12,T12,U12..... of U7800 ic.
I've checked all capacitor under microscope. Usually bad capacitor is visible. I would be tempted to desolder the U7800.

[Pragmatiko]

Found cause of low resistance. I've removed U1200.
Now I don't have low resistance but still I don't have PP1V_PRIM. Maybe cause is PCH not installed?

But I think 44ohm is normal value for PCH. There must be more