Asus Q502L does not boot up properly

[tibimakai]

Re: Asus Q502L does not boot up properly

I'm committed to repair it. I will buy what is needed.
The ferrite bead is already purchased, I just need to replace it.

[caspian]

Re: Asus Q502L does not boot up properly

you need to do lots of measurements. first, start with Post58 when you will have free time.

[SMDFlea]

Re: Asus Q502L does not boot up properly

Can you also test,with no power to the board PR8108,it should be 10K ohms and PQ8101 pin 4 ohms to gnd

[tibimakai]

Re: Asus Q502L does not boot up properly

PL8100 is 450 Ohm and PL8101 it keeps changing, but it is around 16 kOhm, to GND.
PR8108 it measures 9.38 KOhm.
PQ8101 pin 4 to GND, measures: 134.6 kOhm.

No problem measuring a lot, this is my hobby, fixing electronics. I have the equipment to do it, as well. Fluke 189, 87V.
Usually, I repair Onkyo receivers. I used to repair LCD/LED TVs.

[caspian]

Re: Asus Q502L does not boot up properly

without the main battery, plug the AC adapter in but do not turn the laptop on. then, check whether PU8100 gets hot or not. In addition, measure voltage on PL8100 , PL8101 , and pin7 of PU8100. unplug the AC adapter ASAP if PU8100 is getting hot.

[tibimakai]

Re: Asus Q502L does not boot up properly

The IC gets hot, when I plug in the AC.
Before, it used to reboot over and over, with AC. With battery, only started once.
PL8100 and PL8101 voltages are raising and dropping, since it is rebooting. The 5V(PL8101) does not reach 5V, only 3.9V.

[tibimakai]

Re: Asus Q502L does not boot up properly

Soon I will measure pin #7.

[caspian]

Re: Asus Q502L does not boot up properly

In addition, measure resistance on all pins of PU8100 and report if you find any pin with less than 1000 ohms.

[tibimakai]

Re: Asus Q502L does not boot up properly

I'm stopped, because I don't trust my soldering job, on the PWM.
I don't have a microscope and I can't be sure if it is soldered correctly.
Every time I try re-soldering, I'm getting different results. Now I have lost 3V(0.8V), 5V is only 0.8V, but nothing oscillates.

[mcplslg123]

Re: Asus Q502L does not boot up properly

I'm stopped, because I don't trust my soldering job, on the PWM.
I don't have a microscope and I can't be sure if it is soldered correctly.
Every time I try re-soldering, I'm getting different results. Now I have lost 3V(0.8V), 5V is only 0.8V, but nothing oscillates.

It seems Either 3v or 5v(or both) lines are shorted. Might be 2 pins got connected while soldering or reading voltage.

[SMDFlea]

Re: Asus Q502L does not boot up properly

Soldering these small qfn chips without a microscope is very difficult,its 50/50 . USB microscopes are quite good,and cheap,the andonstar ones are ok.Its a good idea to find a few scrap boards and practice on those first,and theres lots of youtube videos

https://www.youtube.com/watch?v=mr1UVPsExiE

https://www.youtube.com/watch?v=c_Qt5CtUlqY

[tibimakai]

Re: Asus Q502L does not boot up properly

I have a cheap Celestron microscope, but unfortunately I can use only to inspect with it. It doesn't have a proper stand.
The biggest problem now is, that I have ripped off, pin #9 trace. I will give it a try, with a thin wire, but ods don't look good, to be a successful repair.

[tibimakai]

Re: Asus Q502L does not boot up properly

I have managed to solder the IC back. Definitely, I have a shorted on the 5V rail.
I have measured all the FETs around the IC, and only only one shows short PQ8103, but after I have removed it, it measures good and short is still there.

[SMDFlea]

Re: Asus Q502L does not boot up properly

With PQ8103 removed which pin measures short.If its pin 4 remove PC8102 and check pin 4 again.If its pin 5 can you desolder the jumper at PJP8101, test if 5V is stable,and also measure without power ohms to gnd .

[tibimakai]

Re: Asus Q502L does not boot up properly

I have re-soldered PQ8103, right after removing it.
Right now, pin 4 is not shorted. Pin 5 is shorted.
Pin 5, shows about 1.3 Ohm. Capacitor is not shorted. It shows 1nF(on PCB w/Fluke 189).
It seems like, the IC(TPS1285B) that I have just soldered in, it may be shorted?

[tibimakai]

Re: Asus Q502L does not boot up properly

OK, I have managed to solder in, the PU8100 and I have low resistance on these three pins.
Pin #14: 2.34 Ohm (+5V SUSO)
Pin #15: 1.94 Ohm (P_5VSUS_DL_30)
Pin #18: 2.32 Ohm (P_5VSUS_LX_30)

[SMDFlea]

Re: Asus Q502L does not boot up properly

desolder the jumper at PJP8101, test if 5V is stable

[tibimakai]

Re: Asus Q502L does not boot up properly

One one side, I measure 19.5V and on the other, only 3.55V.

[tibimakai]

Re: Asus Q502L does not boot up properly

Where should I measure the 5V, at the coil?

[tibimakai]

Re: Asus Q502L does not boot up properly

OK, I have de-soldered PJP8101 and at the 5V coil, I'm getting 0.055V. At 3V coil, I'm getting 0.017V.
I have also noticed, that at Pin #3(PU8100) I have 2 Ohm, at capacitor PC8103).
At 5V coil, I measure 76 Ohm.
PU8100, is still getting very hot very fast. Should I order another one?