Asus GL503GE 3.3 standby voltage low

[brock-s]

An Asus GL503GE laptop arrived that had had a screw dropped on the motherboard while the battery was connected. This resulted in a physical damage to the 3.3v / 5v voltage controller RT6575DGQW (pu28 on schematic, page 40). Additionally, the trace to pin 12 (VIN 19v supply) was burnt.

Replaced the RT6575DGQW with a new one, repaired the damaged trace. Only getting 0.7V instead of the expected 3.3v standby voltage (3V_S5 on schematic).

Replaced the AON7408 PQ60 mosfet from a donor board as resistance was low on the gate (I did not write this value down, as I optimistically thought I was about done with this). Continue to get 0.7V on the 3.3V standby rail.

Replaced the RT6575DGQW with another one (in case it was damaged from the low gate resistance of PQ60. Still no improvement.

I'm hoping someone can look at the current voltages around the voltage regulator and give some suggestions where the problem might be. I've attached a zoomed-in image of the schematic showing RT6575DGQW with the voltages measured.

I've also attached a picture of this region of the board after chip replacement, and the datasheet for the RTS6575D voltage controller.

The schematic and board view are available on BadCaps via this thread: https://www.badcaps.net/forum/showthread.php?t=108079

[mon2]

Re: Asus GL503GE 3.3 standby voltage low

Remove all power. Meter in resistance mode.

Measure the resistance to ground of 3V_S5.

Post the reading.

[brock-s]

Re: Asus GL503GE 3.3 standby voltage low

It starts out in the mega-ohm range but after about 10-15 seconds settles at 13.4kohms.

[mon2]

Re: Asus GL503GE 3.3 standby voltage low

So there is no short on this rail.

With no power -> confirm the resistance values of R3 and R4 which are the feedback resistors that dial the high side voltage to the desired 3v3 value. Do not power up without these resistors as this could cause the same power rail to overshoot and kill all voltage sensitive parts on this line.

Also, with no power, confirm the details of the high and low side mosfets (PQ60 & PQ62).

Measure the resistance across:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement for PQ60 and PQ62. Checking if the mosfets could be leaky and forcing this rail to be lower than expected.

[brock-s]

Re: Asus GL503GE 3.3 standby voltage low

R3 (PR434) measures 9.56kohms out of circuit.
R4 (PR438) measures 14.69kohms out of circuit.

PQ60: Rsd = 0.46Mohms
PQ60: Rgd = off-scale (>40Mohms)
PQ60: Rgs = off-scale (>40Mohms)

PQ62: Rsd = 0.45Mohms
PQ62: Rgd = off-scale (>40Mohms)
PQ62: Rgs = off-scale (>40Mohms)

Both Mosfets measured out-of-circuit.

Both Mosfets Rsd was 2-3Mohms before measuring the Rgs - i'd guess the gate charged slightly due to the measurement being taken. (using Fluke 12)

[mon2]

Re: Asus GL503GE 3.3 standby voltage low

Looks ok to me. Consider to replace this regulator. Should be cheap on AliExpress. Do update this thread with your progress.

[brock-s]

Re: Asus GL503GE 3.3 standby voltage low

I actually had purchased multiple regulators (RT6575D) from Digikey when I placed the order as they were cheaper than the shipping. As such, I have new spares. Replaced the regulator with one of these. Still measures 0.735V on 3v_S5 trace.

[mcplslg123]

Re: Asus GL503GE 3.3 standby voltage low

3V LDO and 5V LDO present?

[Sephir0th]

Re: Asus GL503GE 3.3 standby voltage low

Could be something wrong with the feedback line. Look whether Resistors there are in specs.

[mon2]

Re: Asus GL503GE 3.3 standby voltage low

Post #5

[Sephir0th]

Re: Asus GL503GE 3.3 standby voltage low

Thanks for the heads up. After a second look, +5V_S5 seems to be missing even completely and could be the origin of the issue. This power rail is supposed to be present too and has to be inspected the same way as before. the Mosfets, feedback resistors and resistance to GND of +5V_VS of course.

After that there is even more to check. The components on the bootstrapping line for example and whether is something wrong with the charge pump, creating the 15VPCU.

[brock-s]

Re: Asus GL503GE 3.3 standby voltage low

mcplslg123: yes to both (3V LDO = 3.3V; 5V LDO = 5.03V)

Regarding the 5V_S5 circuitry:


Feedback resistors:
R1 (PR432) measures 23.95kohm out of circuit
R2 (PR437) measures 15.43kohm out of circuit

PQ59: Rsd = 3.2Mohms
PQ59: Rgd = off-scale (>40Mohms)
PQ59: Rgs = off-scale (>40Mohms)

PQ61: Rsd = 2.9Mohms
PQ61: Rgd = off-scale (>40Mohms)
PQ61: Rgs = off-scale (>40Mohms)

+5V_S5 resistance to ground measures 2.2Mohms

Bootstrap components

Regarding the 5V_S5 circuitry:
PR431 = 5.45Kohm (this is high, found a 3.3ohm resistors (that measures about 4.0ohms), and replaced it.)
PC338 = 0.229uF

Regarding the 3V_S5 circuitry:

Bootstrap components
PR430 = 3.9ohms
PC337 = 0.229uf

Note: PR431 found bad and replaced it. Now the 5V_S5 is 0V and the 3V_S5 is 0.130V.

[brock-s]

Re: Asus GL503GE 3.3 standby voltage low

VCLK (pin 19) of the charge pump does not go anywhere - the components shown in the schematic have an asterisk and are not populated on this board. Any other suggestions on what to check next?

[reformatt]

Re: Asus GL503GE 3.3 standby voltage low

Check for shorts after each +3V and +5V load switch, especially the one for the PCH.