Acer AN715-71 LA-E911P...

[titomno2]

Hi,
Trying to fix a motherboard that not starting.
At first it appears to have a shorted 3V/5V componentPU401 (heating up and consumption was high).
After replacing still no 3.3V everything seems in place except one capacitor removed.

ENDLDO (#11) is 4.5V when 19.5V is applied.
+3VALWP [#14) is 0V when 19.5V isapplied.
+19BVB_3V (#2,3,4,5) is 19.6V and present.
BST_3V {#1) is 0V (don(t know if it is normal)
LX_3V (#19 and 20) is 0V
SPOK_3V (#9) is 0V
3V_EN (#12) is 0V (I checked the RB15 and RB15 seems ok, also DB1 and DB2 are OK in diode mode).

Please tell me if other measures will be usefull, I'm a little bit loss.

Thank you

[mon2]

Flux and clean up the following pads. The pins look to be shorted.

[titomno2]

hi mon2
Both pad are on the ground that's why I let the pin shorted.

I will give it a try to check all other pads.

[titomno2]

Made better solder joint even if the two pin shorted are for ground.

I also checked all voltage at each pin on the SY8286 ic chip:

BS, Pin #1 => 0V
IN, Pin #2,3,4,5 => 19.58V
LX Pin #6, 19, 20 => 0V
PG Pin #9 => 0V
EN Pin #11 => 0V
ILMT Pin #13 => 0V
FB Pin #14 => 0V
BYP Pin #15 => 3.3V some times and 0V most of the time (a bit strange as it seems not to be used on the motherboard schematics)
VCC Pin #17 => 0V (my issue :-)).

I tried both IC (the one removed as it was heating up and the brand new one, readings are the same).

I think something is wrong somewhere but nothing obvious on the board (not burned or missing component except a decoupling capacitor on the charging circuit).

Any idea will be strongly appreciated.

[piernov]

SY8286 and SY8286B are not the same IC, datasheet won't fully match, rely on schematic/boardview. As always, heating 3V regulator and missing 3V LDO output is generally caused by a short to ground on the 3V LDO output, often inside the EC or the PCH, dozens if not hundreds of cases like that on this forum.

[titomno2]

Both of IC I have are SY8286BRAC as indicated in the boardview.
So to determine if my short is somewhere on the board or the IC chip, should I try to remove the chip and apply 3V with stabilised power supply and check if anything is getting hot?
Or at least checking the yellow elements to find any short before injecting voltage?

[mon2]

Hi. Good review.

1) Remove all power. Meter in resistance mode. Measure the resistance to ground of this LDO rail @ pin 17. If there is a low resistance on this rail then someone is shorted and needs to be reviewed.

2) The enable for this same LDO rail is the ENLDO_3V5V signal fed into pin # 11 (EN2). This voltage is also 0 volts.

Investigate the resistor based voltage divider for this ENLDO_3V5V signal. Confirm the voltage to ground on each side of the PR402 resistor.

3) No injection needed unless we know there is a short condition on the rail. The resistance check will confirm this.

[titomno2]

Hi,
1) I read 48.42kOhms (so no short there).
2) My bad I Have wrongly copied the value on the first page I read 4.49V opn the EN #11, and the PR402 measured at 499K and P404 measured at 150K (but off the board I'm not able to measure one the meter is not catching the value and the other I have MOhms)

[mon2]

Ok - to summarize, you DO have a valid enable signal. Be sure that this voltage is reaching this regulator's enable pin.

If there is no short on this LDO rail and you have a valid enable then you must have a 3v rail present. If not, this IC is not properly soldered onboard. Consider to flux and reflow it well till it sinks onto the PCB pads. Just use low air pressure and tight circles. Do not lose the other parts nearby.

Plan B is to convince piernov to do a house call Been hinting that for years.

[titomno2]

I have a valid enable signal. checked under magnifying camera and the bad are correctly soldered.
Everyhting was reflow as you mentionned and no change.

Don't know about the plan B :-) whatever I will go on vacation...

Could the IC I have be dead out of the box ?

[mon2]

With all due respect, I think the issue could still be the soldering. There is a metal belly = EP under this IC. Review the removed part. It is possible that pad is not properly soldered onto the PCB. Consider to reflow with ample flux and use tweezers on 2 edges to gently push the chip away and allow the part to naturally bounce back into position. Keep flowing the hot air with low pressure in circles to keep the solder in liquid mode.

Not too much heat so that the PCB does not burn but enough to do the job. The part should sink onto the board.

From where did you source this IC? Not sure but check if available from local stores / online or of course Aliexpress. Use only stores with high ratings. They are cheap enough to source more for testing.

[piernov]

Short to ground on the RTC power rail for example won't show up directly as low resistance on the 3V LDO output since there's a diode inbetween.
Injecting some current on the 3V LDO output can help detect if there's a problem down the line, a current consumption of a few dozen mA or more would indicate a problem.

[titomno2]

Thank you mon2, i will try to remove gently the ic chip, check the soldering (and don't hesitate, I know I have to improve a lot m soldering skills but step by step I'm becoming better at this game).
But according to piernov, may be I will try the voltage injection as I have a thermal camera it could help me to find if something else is in bad shape.

[mcplslg123]

If i'm not confused, then as per OP only ENLDO is present and 3V_EN is missing, So logically only LDO pin should have voltage in standby.
3V_EN will come only after switching.
Since resistance check to gnd on LDO pin is high, very likely its the IC itself which is bad/badly soldered.
however, if there is short in RTC section,the IC will heat up in standby. Can you confirm the IC is heating up or not?

[titomno2]

when plugged in the 19V adapter (stabilized power supply) I have no consumption and 19V is present at the ic chip which is not getting hot (confirmed that I have not consumption on the 19v power input (0.000Amps).
I checked with the thermal camera all the board and noting is heating up.

I have corrected the values hereafter, Hope it clarify the situation.
BS, Pin #1 => 0V
IN, Pin #2,3,4,5 => 19.58V
LX Pin #6, 19, 20 => 0V
PG Pin #9 => 0V
EN Pin #11 => 4.495V
ILMT Pin #13 => 0V
FB Pin #14 => 0V
BYP Pin #15 => 3.3V some times and 0V most of the time (a bit strange as it seems not to be used on the motherboard schematics)
VCC Pin #17 => 0V (my issue :-)).

I will solder a wire on the 3V LDO and inject voltage to see if there is any sort of reaction (current draw and/or thermal imagery).
If no reaction => I will redo the soldering (cleaning everything and replace with leaded solder to lower the temperature during soldering). mon2 The Ic chip was purchased on a local supplier via ebay (I already purchased many ic chip from him without issues)
I use antisattic tweezers bu maybe I may have damaged it during the first soldering (it is a lesson I learn to check twice the soldering joint and the pins are correctly in line).

thank you to helping me with situation, it give me a better view and I will learn new things.

[titomno2]

So here are the results of the first test with injecting voltage.
Applied 3.1V on the VCC Pin #17 => 0.02A is drawn on the power supply (DH3 is getting slightly hot (not burning)).
Applied 3.3V on the VCC Pin #17 => 0.03A is drawn on the power supply (DH3 a bit hotter but nothing very impressive).

Cut off everything, applying 19.5V and then applied 3.3V, I have 3.3V on the keyboard button, pressing the power button I have a low consumption on the main power supply (19.61V 0.066A ~1.293W during few seconds).
During powering up the PCH present a hot point on the corner of the die (not very hot as it is only 1.2W but not good).

So I think I have to focus on the DH3 which is on the RTC...

Last time I have encounter an RTC short the processor package was fried (PCH integrated on the dell E5450 => dead). :-(

Before doing anything stupid I am open to any good advices.

[piernov]

Measure the resistance to ground on +RTCVCC.

[titomno2]

I assume I may make the measurement between DH3 pin #1 and any ground part on the board.
If yes I will do it on next monday as I'm far away from the motherboard right now. 😀
My appologies for delay to my next answer; measurement will be done next monday (at best).

[titomno2]

Hi Guys,
Back from holliday, hope everyone is in good condition 😁.
So I made some measurement (without power at all, battery, rtc battery and power supply removed).
Pin #1 +RTCVCC => GND = 156Ohms (NOK).
Pin #2 +CHGRTC => GND = 44.44 kOhms (OK ?)
Pin #3 N123854884 => GND = 1.4MOhms (OK ?)

Measured resistors and capacitor on the RTCVCC path
RH60 => 19.82kOHms (20K => OK)
CH60 => 155Ohms (waited for at least kOhms)
CH59 => 155Ohms (waited for at least kOhms)
PR212 => 99kOHms (100K = OK)

On the other side of the board
RH63 => 19.84kOhms (20K => OK)
RH12 => 4.47Ohms (1Mohms => NOK)

So, should I tried to change the resistor RH12 with a good one 1 Mohms ?
Or could be an issue on the PCH (Hope not 😱)

Before doing anything wrong, wanted to have some advice from you guys.

Best Regards!

[piernov]

You can always try your luck at removing the 2 capacitors, but it's gonna be a dead PCH as usual.