820-00244 - PP5V_S5 woes

Atomrepair

Member
This board has no visible damage. It seemed like a straightforward issue, as I found PP5V_S5 to be shorted to GND. I traced it to C8270, which had shorted for unknown reasons. After removing it, the short was gone, but still no power on PP5V_S5. I replaced U7650 with a good looking one from a donor board. Machine turned on and I got an image on screen, but it shut down mid-boot and wont turn back on.

Measured: PP5V_S5 is 'jumping around'. It has a sawtooth pattern on my scope.
I first suspected U7650 - may have been a bad chip or poor soldering. I took it off and replaced it with another one. No change.

Other components on the PP5V_S5 rail look fine. No liquid or other damage found anywhere.

Measurements:
PM_SLP_S5_L is mostly 0V but has little spikes up to ~1.5V

P5VP3V3_VREF2, S5_PWR_EN, P3V3_S5_EN and S5_PWRGD are all showing a block pattern on scope.

PPBUS_G3H is at 8.7V

Where to from here?
 

2informaticos

Administrator
Staff member
Try first to start in SMC bypass.

"PM_SLP_S5_L is mostly 0V but has little spikes up to ~1.5V"
Then xV_S4 voltages should pulse too.
Check if PM_SLP_S4_L and xV_S3 voltages pulse.
Do the same for PM_SLP_S3_L and all xV_S0.
Any pulse at ALL_SYS_PWRGD?

BTW, check the board alone, w/o tp/kb connected.
 

Atomrepair

Member
Yeah, I'm working with just the board.
Found out PP5V_S4 is shorted to GND.. I hooked up lab supply to it; Nothing getting hot with 4A at 1V.
Short to GND inside the board, I guess? :(
 

Atomrepair

Member
Nothing on the board heats up, at least not quickly; my (fairly thick) wire soldered to the board does smoke and its insulation melts at 5V / 10A (my power supply's max current)
If I leave it on 1V for a longer period a large area around my jumper's location heats up, but nothing specific. (I've attached my wire at pad 1 of C7657)
 

2informaticos

Administrator
Staff member
An IR cam can help you in this case.
FLIR is the best option, but Seek Cam (phone adapter) could be good enough too.
If your desk power supply is 10A limit, then start with 1V and increase voltage until get 9-9.5A.
If power supply indicates 10A can get stuck and doesn't really inject.
 
I have a FLIR pro on a ipad on my bench. I consider it one of my most important tools. I grab that thing multiple times a day. It will pay for it's self the first week you own it. The software interface glitches and it is a pain in the ass at times but I would not part with it.

You defiantly want a "Pro" the resolution is so important. FLIR also overlays visual data with IR data so you can pinpoint the exact part. I can literally identify a specific cap on a phone board and pluck it off. I use it on iPads all the time and MacBooks when trying to find which Tantalum is dead. I have made thousands off the thing!
 
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Atomrepair

Member
I'll think about it, but not in such a hurry that I'll get one just for this repair. I'll lift stuff off the board for this rail and see where that gets me.
 

Atomrepair

Member
Frustrating board.. I found out why 5V_S4 was short to GND; Q7660 was faulty. internal short, probably. I replaced it, Short gone, but no voltage on the rail still. Fed the rail 5V through my lab supply, no issues there.

Replaced U7650 again to rule that out. Got 8.7V on 5V_S4. Q7660 burnt up again.

Found that R7672, R7673, R7693 and R7692 are way off from what the schematic says they should be:

R7672 was 25K, schematic says 10K
R7673 was 2K, schem says 1K

R7692 was 17K, schem says 15K
R7693 was 2.7K, schem says 1K

This seems a little dubious to me, for all those resistors to be off like that, but I dont have a donor boards for this model to verify. Anyone know?

Replaced Q7660, U7650, R7672, R7673, R7692, R7693, C7673 and C7693 all at once.
Hooked up adapter, heard a high pitched whine, notice amperage going up - whine stops, current draw back to 0.01 (voltage 20). Hooking it up again results in no whine and 0.01 Amps. So, it seems that U7650 is dying every time I replace it, but I'm out of ideas on what might be causing it.
 

Atomrepair

Member
Dove into this board again today. Recap;

1. PP5V_S5 was shorted to GND through C8270. I replaced C8270 and U7650. Machine worked, then stopped.

2. PM_SLP_S5_L was mostly 0V but had spikes. P5VP3V3_VREF2, S5_PWR_EN, P3V3_S5_EN and S5_PWRGD all had block shaped waves on scope. I found out that Q7660 was causing a short to GND and replaced it. Short gone, block shapes gone on other rails and everything seemingly ok, but 0V on PP5V_S4.

3. Replaced U7650 again and got 8.7V on PP5V_S4. I failed to notice a bridge between C7650 (PPBUS) and C7653 (P5VP3V3_REG3). Ouch. This is what caused PP5V_S5 to go to 8.7V and probably killed U7650 again. It probably did more than that.

Today, I removed the bridge between C7650 and C7653, replaced U7650 and Q7660.
Machine wont boot in SMC bypass. Power draw 0.02A at 20V.
measurements:
PM_SLP_SUS_L3,3V
check U7650 inputs
P5VP3V3_VREG33,3V
P5VP3V3_VREF22V
PPBUS_G3H8,7V
PP3V3_S53.3V
PP5V_S55V
S5_PWR_EN3,17V
S5_PWRGD3,3V
PP5V_S40rising resistance (caps)
P5VS4_DRVL083KOhm
what does PP3V3_S5 have that P4VS4 is missing?
PM_SLP_S5_L / P5VS4_EN016KOhm
ALL_SYS_PWRGD018,3KOhm
PM_SLP_S4_L097KOhm

Having had PP5V_S4 at 8.7V, anything on that rail might be fried, including the SMC. Nothing special happens when I inject 5V into the rail now (0.08A).
Is there anything left to do to see if this is salvageable?
 
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