mac 820-00850-A No power on

[reset1986]

i have this mac that won't start, no fan rotation, i took measurements and missed the s5 rails

PP3V3_G3H 3.3V

PPVIN_G3H_P3V3G3H 12V

PP20V_USBC_TA_VBUS 20V on two connectors

PP5V_S5_LDO fluctuates from 0 to 5 there are no shorts

PM_SLP_S5_L 0V

PP3V3_S5 0V

PP1V8_S5,

PP1V05_S5_PCH_VCCDSW


PP1V24_S5_PCH_VCCDPHY,

PPVPCORE_S5

all missing, what can i check? i noticed the chip
T2 U3900 heats up slightly but there are no shorts

[mon2]

Re: mac 820-00850-A No power on

PP5V_S5_LDO fluctuates from 0 to 5 there are no shorts

What is the resistance to ground of this rail ? Something is causing this fluctuation.

Is the P5V_P3V3G3H_LDO_EN which turns in the above LDO rail ON/OFF fluctuating as well ?

[reset1986]

Re: mac 820-00850-A No power on

What is the resistance to ground of this rail ? Something is causing this fluctuation.

Is the P5V_P3V3G3H_LDO_EN which turns in the above LDO rail ON/OFF fluctuating as well ?

they did not short, resistance PP5V_S5_LDO around 100K

also P5V_P3V3G3H_LDO_EN is mobile, it varies from 0V to 1.85V resistance 49Kohm

Thank you

[mon2]

Re: mac 820-00850-A No power on

The enable is linked to the PMU.

What is the voltage of PMU_PVDDMAIN_EN ? Is it also fluctuating ?

What is the voltage of P3V3G3H_EN_R ? Is it also fluctuating ?
* this is a weird one - is this signal actually used ? It leads to parts in the schematic marked as not stuffed.

[reset1986]

Re: mac 820-00850-A No power on

The enable is linked to the PMU.

What is the voltage of PMU_PVDDMAIN_EN ? Is it also fluctuating ?

What is the voltage of P3V3G3H_EN_R ? Is it also fluctuating ?
* this is a weird one - is this signal actually used ? It leads to parts in the schematic marked as not stuffed.

PMU_PVDDMAIN_EN cell from 0 to 2.6V

also P3V3G3H_EN_R from 0 to 0.30V

[reset1986]

Re: mac 820-00850-A No power on

The enable is linked to the PMU.

What is the voltage of PMU_PVDDMAIN_EN ? Is it also fluctuating ?

What is the voltage of P3V3G3H_EN_R ? Is it also fluctuating ?
* this is a weird one - is this signal actually used ? It leads to parts in the schematic marked as not stuffed.

I have noticed that all tensions fluctuate,
PP3V3_G3H also goes from 2.4 to 3.42

PPVIN_G3H_P3V3G3H ranges from 12.20 to 12.40V

only PP20V_USBC_TA_VBUS stable 20V

tips?

[mon2]

Re: mac 820-00850-A No power on

PP3V3_G3H also goes from 2.4 to 3.42

Not normal. This is an 11A power rail. Does your meter have good batteries ?

Remove all power. Meter in resistance mode.

Check the resistance to ground of PP3V3_G3H.

What is the measurement and the scale used on your meter for this check ?

U7650 may be defective.

[reset1986]

Re: mac 820-00850-A No power on

Not normal. This is an 11A power rail. Does your meter have good batteries ?

Remove all power. Meter in resistance mode.

Check the resistance to ground of PP3V3_G3H.

What is the measurement and the scale used on your meter for this check ?

U7650 may be defective.

ok PP3V3_G3H high resistance,
I found l7600 PP5V_G3S resistor 22 ohm, it seems to me low, removed l7600

P5VG3S_VSW high resistor

PP5V_G3S U7650 22 ohm

[mon2]

Re: mac 820-00850-A No power on

L7600 PP5V_G3S resistor 22 ohm

Yup. That is low on the consumer side.

Do you see any damage nearby this regulator ? Any rough looking caps that you would not want to meet in a dark alley ?

Do you have a bench power supply ?

With the removed coil L7650, you could consider to inject 0v8 (personally always start with a low voltage in case the CPU mosfet is shorted, etc. downstream) and check for heated caps. You can use a thermal camera or IPA.

[reset1986]

Re: mac 820-00850-A No power on

Yup. That is low on the consumer side.

Do you see any damage nearby this regulator ? Any rough looking caps that you would not want to meet in a dark alley ?

Do you have a bench power supply ?

With the removed coil L7650, you could consider to inject 0v8 (personally always start with a low voltage in case the CPU mosfet is shorted, etc. downstream) and check for heated caps. You can use a thermal camera or IPA.

removed u7650 the resistance returned to high in l7600, problem on tps51980a

I'm looking for a replacement

[rizalle]

good