820-01814 Won't power on, PP5V_G3S shorted

[barry101]

Hi,

I would greatly appreciate some guidance.

I have a 2019 A1990 15" MacBook Pro 820-01814 logic board, EMC 3359 that won't power on.

Owner stated his wife inserted a USB memory stick and now the laptop doesn't work.

Board is clean, no sign of liquid or damge/missing components.

PPBUS_G3H is 12.3V.

Found PP5V_G3S tries to turn on but turns off immediately and is only 0.2 ohms to ground. Other rails are not shorted.

No other work done to board other than removing it from chassis and probing. Using Apple charger.

Would appreciate any recommendations to ensure I don't damage the GPU or CPU before removing PP5V_G3S coil to determine which side is shorted and then inserting 5V to see what heats up. Also, are there any common failures give the memory stick as the theoretical cause.

Thanks
Barry

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Remove all power -> meter in resistance mode.

Measure the resistance to ground @ L7600 (either side).

What is the measurement?

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Hi, Thanks for the reply. Reads 0.2 ohms to ground.

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Would you have an adjustable DC power supply?

At this low resistance, could be a shorted capacitor on this rail. Suggestion is to dial up the power supply to 1 volt (not higher) and inject this voltage onto the same inductor point.

The current will spike, as it should due to the low resistance and cause the shorted component to heat up. With this low resistance, it is common to see a tantalum capacitor split / crack open. Then remove that component and test again to see if the shorted condition is resolved.

In this process, you do not apply the external power adapter nor the battery - remove both.

Reference (worth a view):
https://www.youtube.com/watch?v=wp1dPG9_N1w

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

I'll try that. Do you recommend lifting the inductor to determine which side is shorted first and inject voltage onto the shorted side only or just leave the inductor in place?

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Yes. That is a good idea but not absolutely necessary. Flux it well and wait till the solder melts and gently lift one leg of the inductor. Suspecting the fault is downstream (consumer side).

Either way, the injection will heat up the component for a quick identification.

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Got it, thanks. I'll let you know how it turns out.

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Lifted L7600 load side. Load side was shorted to ground.

Injected 1V on load side and set current limit to 4.9Amps. Read about 0.6V at injection point and drew about 2.3 amps.

After about 10 minutes the only place that got to 135 degrees F was an empty spot midway between L7660 and U7660 about 1/4" toward fan cutout. No components at that location on either side of board.

However, L7660 itself got burning hot to the touch although the infra red temperature gauge only showed it to be about 96 degrees. Voltage to ground at both side of L7660 was 0 volts. Neither side of L7660 was shorted to ground or to L7600.

Could there be an internal short to ground in the vicinity of L7660 and U7660?

There is a path for PP5V_G3S to the no-stuff fan connector near that location that could reasonably be assumed to run under that empty location on the board. Measured all of the unused fan connector pads and they were at 0 volts to ground.

The PPBUS_G3H capacitors got very slightly warm. Not sure why they drew power, the board was naked on the bench with no power connected.

Any suggestions?

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted



The attached photo shows the warm spot at the tip of the probe. L7660 and the no-stuff fan connector (I presume that is what the pad is for) are also shown.

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

To confirm, the injection is on the other side of the inductor L7660 so the inductor is in the path of the short? If yes, inject on the other side. The inductor is a large length of wire so it will heat up due to the hard short.

Test again and see who heats up (without L7660 in the path).

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Closer examination of the traces to the fan connector pin 1 shows PP5V_G3S not going under the warm/un-occuppied area of the board. It passes to the left of L7660 so I'm not sure why that spot got warm. That leaves the question as to why did L7660 get so hot?

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

The injection point was at the output of L7600, not the input to L7660. That's why I don't understand why L7660 go hot. Please the photo I attached to the previous post.

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Will check once back at the office. Need to check the board view file. Should be back in an hour or so.

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Thanks so much! Appreciate your help!

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

See attached. Remove all power / no battery. Meter in resistance mode.

Measure the resistance of the dual mosfet @ U7600.

Measure:

source & drain
source & gate
gate & drain


Check both mosfets inside U7600. Post the measurements.

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Here are the requested resistance readings with L7600 load side lifted:

UPPER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 1): 6.5K RISING TO ABOUT 10K AND STILL GOING UP
SOURCE TO GATE (PIN 4 TO PIN 3): 90K
GATE TO DRAIN (PIN 3 TO PIN 1): 100K

LOWER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 9): 5.6K
SOURCE TO GATE (PIN 4 TO PIN 5): 93K
GATE TO DRAIN (PIN 5 TO PIN 9): 88K

Does U7600 matter since the short is on the load side of L7600?

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

To me, the resistance checks on this mosfet look to be too low.

reference:
https://electronicsbeliever.com/how-...-is-defective/

Perform the same resistance check @ U7660 (dual mosfet).

Does U7600 matter since the short is on the load side of L7600?

Concern is why voltage injection @ L7600 is causing inductor L7660 to heat up.

Be sure that you are injecting the voltage @ L7600, pin #1 (downstream / consumer) side of the inductor.

Confirm again the resistance to ground @ L7660.

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Re-ran U7600 resistance measurements being sure to discharge the gate and have the black probe on the gate. Same results repeated here for ease of comparison with U7660.

UPPER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 1): 6.5K RISING TO ABOUT 10K AND STILL GOING UP
SOURCE TO GATE (PIN 4 TO PIN 3): 90K
GATE TO DRAIN (PIN 3 TO PIN 1): 100K

LOWER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 9): 5.6K
SOURCE TO GATE (PIN 4 TO PIN 5): 93K
GATE TO DRAIN (PIN 5 TO PIN 9): 88K

Here are the requested resistance readings for U7660 (in this case L7660 is in place) with gate discharged and black on gate:

UPPER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 1): approx 30k
SOURCE TO GATE (PIN 4 TO PIN 3): 91K
GATE TO DRAIN (PIN 3 TO PIN 1): 110K

LOWER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 9): 28K
SOURCE TO GATE (PIN 4 TO PIN 5): 129K
GATE TO DRAIN (PIN 5 TO PIN 9): 87K

L7660 resistance to ground is 18K.

Voltage was definitely inserted into L7600-1 as you can see in the photo I sent earlier.

Checked L7600 pin 1 to 2 resistance (measured at the pads since the L7600 is lifted) is 5.6K which seems correct give R7672 is 4.87K and R7673 is 698 ohm and the are in series.

Seems like U7600 Source to Drain resistance is lower than U7660 (10K vs 30K).

[barry101]

Re: 820-01814 Won't power on, PP5V_G3S shorted

Could this explain both the short to ground on the 5V L7600 and power heating the 3V L7660?

What if:

PP5V_G3S short to ground is internal to U7650 on CSN1
U7650 has an internal path from CSN1 to CSP2
Current flows through R7692 to L7660 and then out to the load.

This would happen even if L7600 is lifted on the load side.

[mon2]

Re: 820-01814 Won't power on, PP5V_G3S shorted

U7650 = TPS part is notorius for failures. Louis mentions this in a few of his videos. If you have the tools, consider to carefully flux and remove this component to test the theory of the short. Keep the air flow as low as possible or protect the nearby SMD parts so they do not go flying.

Take a pic of the topside of this part for the pin #1 orientation.

Before proceeding, remove all power, measure the resistance between L7600, pin #1 = PP5V_G3S to PPBUS_HS_OTH5V.

Also test,

L7600 (pin #1) to PP3V3_G3H_T.