Asus X554L No Power

[StefanNg]

Hi BadCaps

I want to try my first component level repair on this board. It is a Asus X554L with X555LD main board rev. 3.6. I search the forum and online, downloaded any resources available. The boardview I get is not exactly the same, this main board may have many variant, not all component shown in boardview exist on actual board.

The board do not power on, no charging light, nothing. Item already check include
1. MOSFET PQ8801 PQ8802, source +19.5v, drain +19.5v, gate +24.3v
2. Power switch SW5601, +1.96v, below required +3v.
3. IC PU8101 (component with marking 2N=, Richtek RT8249C) is heating up, pin 3 +3VAO +1.98, pin 13 +5VAO +5.06v

I read some thread, RT8249C heating up doesn't mean IC is shorted, maybe it working in that way, but I don't know where to trace next. Hope to get guidance and thank you in advance.

[mcplslg123]

Re: Asus X554L No Power

It could be both-The IC itself may be bad or there is some shorted/leaky component on +3VAO rail. Cut the track between PSL8104 so that +3VAO is separated from +3VA rail. Now check again voltage on Pin3 of PU8101(you can measure the same on Sl8104,pin1.

If the voltage rises to stable +3V, then there is some shorted component downstream and you may need to inject voltage on SL8104,pin2 to find out what is getting hot.

However, if the voltage still remains +1.98V, then the ic is definitely bad.

Update us about your findings.

[StefanNg]

Re: Asus X554L No Power

Hi, mcplslg123

I manage to cut open PSL8104. First time do on a multi layer PCB, so I did it slowly.

+3VAO is now +3.3V, +5VAO 0V (+4.9V if I short the gap I cut on PSL8104), the IC is good. Maybe is a bad news for me because now I need further deal with the whole +3VA rail.

The only safe way to do voltage inject is using a bench top power supply? I don't have it and I will need to learn the correct way to use. While I source for a suitable power supply, I am welcome any suggestions on alternative way to repair the main board.

Thank you

[mon2]

Re: Asus X554L No Power

An adjustable power supply is a required tool for power injection. The power supply will be $50-$100 usd on AliExpress.

You can consider a short killer tool but it also needs to be adjustable. Keep at under 1 volt to remain under the max cpu voltage.

Watch this video:

https://youtu.be/WQMQ3tm5Dho

[StefanNg]

Re: Asus X554L No Power

I watched few voltage injection video. Voltage is inject from the point shorted to ground, current injected will flow thru shorted caps, then heat up the bad cap.

In my case, PSL8104 pin2 is not shorted to ground, resistance is 90kOhm. Is it safe to do voltage injection? If not safe, what should I check next?

Thank you.

[mon2]

Re: Asus X554L No Power

Voltage / current injection will not work for this case. You do not have a short on this line. Injection is only for low resistance rails.

Instead, study the enable pins and soldering of this part if the rail is not powering on.

[mcplslg123]

Re: Asus X554L No Power

Yes, agreed with@mon2. Resistance is not low ,so voltage injection wont work. I expected a low resistance on Pin2 of SL8104 after cutting the track.

[StefanNg]

Re: Asus X554L No Power

Should I say the rail is powering ON? It receive +3V from PU8101, but the rail voltage dropped to around +2V, there is continuity on it. Because of the voltage drop, power switch is not functioning.

The +3VA is connected to few parts. I need to find a way to narrow down.... Is this main board still worth a try?

[mon2]

Re: Asus X554L No Power

With no power, measure the dcin mosfets' resistance across their pins. One of them may be leaking to still power the logic board.

Source and drain
Source and gate
Gate and drain

[StefanNg]

Re: Asus X554L No Power

Please correct me if any point I get it wrong.
I assume dcin mosfet means PQ8801 and PQ8802
The mosfet marking is M0930M, I could not find datasheet, so I don't know which type of mosfet I have. I test it on diode mode, roughly guess where to contact the +ve and -ve probe. I took pin1 as drain, D
______________PQ8801 PQ8802
S(-) and D(+) 16MOhm 16MOhm
S(-) and G(+) 1136kOhm 1030kOhm
G(-) and D(+) 16.5MOhm 16.5MOhm

I have no idea what I am looking at

[mon2]

Re: Asus X554L No Power

Correct. See attached.

The highlighted parts are the 2 x DCin mosfets. They are acting like switches that allow / stop the power from your external power adapter from reaching the main power line.

Respectively each mosfet is enabled or disabled via the voltage on the GATE pin # 4 of this package.

On N-channel mosfets, the GATE pin must be HIGHER than the voltage that is being passed on the source / drain pins. That is, if your adapter is ~19v then the gate voltage is often around 19v + 6 volts (boosted by the charger IC) = ~25 volts to turn ON the mosfet.

Start with measuring the voltage on pin # 4 of each of these mosfets with the power adapter connected.

Red probe to pin #4; black meter probe to ground; meter in 20V or higher DC volts mode.

Post your measurements.

[StefanNg]

Re: Asus X554L No Power

I check on this section previously, I will re-check it again tonight. In previous measurement Pin#4 is +24.3v, Pin#1 is +19.5v. Source voltage is present for both mosfet, +19.5v. Is this measurement sounds OK? Gate voltage is slightly lower but Drain voltage is present.

Just an additional thought. Both mosfet is interconnected for Pin#1 and Pin#4. With power adapter connected, only PQ8801 is check in this measurement?

[StefanNg]

Re: Asus X554L No Power

I temporary patch up PSL8104, connect adapter and took big coil voltage measurement on the main board

PL8003 0v
PL8101 5v
PL8102 3.32v
PL8201 1.09v
PL8301 1.37v
PL8501 0v
PL8502 0v
PL8801 3.19v

Compare to boardview information, I feel this result looks normal. Hmm..... what else I can check further?🤔

[mon2]

Re: Asus X554L No Power

On the coils with 0 volts, remove all power and with the meter in resistance mode, check the resistance to ground.

[StefanNg]

Re: Asus X554L No Power

Hi @mon2

I follow your instruction
PL8003 60.4 Ohm
PL8501 6.2 Ohm
PL8502 6.2 Ohm

PL85xx is located close to GPU U7001, PL8003 is located close to processor U0301

[StefanNg]

Re: Asus X554L No Power

I watch some asus main board repair video. Is PL8801 part of the battery charging circuit? If yes, then 3.19v seems to be too low, it need to be around 12v.

IC PU8101 +3VAO is connected somewhere near to IC PU8800, which may work together with PL8801? Or could it be some problem near to EC U3001? Is there a way to further checking?

I still haven't find the way out yet. Hmm..... any suggestion?

[mon2]

Re: Asus X554L No Power

Remove all power. Meter in DIODE mode.

Red meter probe, yes RED, to ground.

Black meter probe to one side of PL8801.

What is the reading? The last 2 pages of the repair guide offer diode mode values.

What are the topside markings of the IC near PL8801?

[StefanNg]

Re: Asus X554L No Power

Hi @mon2

What is the reading?

Reading is 470

What are the topside markings of the IC near PL8801?

Marking is BQ735. I make a search, it is Texas Instruments bq24735 Li+ Battery SMBus Charge Controller.