Asus Q502L does not boot up properly

[tibimakai]

Re: Asus Q502L does not boot up properly

I have removed PQ8100, PQ8101 and opened up PJP8102, PJP8103, PJP8104, and PJP8105. Then, I have reconnected PJP8101. I'm measuring a resistance on PL8100, around 4.2MOhm, slowly dropping. Just to know, that PJP8100 is connected.

[caspian]

Re: Asus Q502L does not boot up properly

now without reconnecting any PJP..., replace PQ8100, PQ8101, PQ8102, PQ8103, and PU8100 by new ones. replacement IC for PQ8100, PQ8101, PQ8102, PQ8103 should be exactly of the same model of the old IC. then connect power to the mainboard and measure voltages. but do not press the power button.

[tibimakai]

Re: Asus Q502L does not boot up properly

Placed the order for new transistors, it will take around 3-4 weeks to arrive. PU8100 is already here.
I will be out for a while, until these arrive.
Thank you very much, for your help.

[tibimakai]

Re: Asus Q502L does not boot up properly

I'm about to solder in the new components, but before I do that, I would like to know, what exactly I have to measure, before I turn it on?

[caspian]

Re: Asus Q502L does not boot up properly

first solder PQ8100, PQ8101, PQ8102, PQ8103, and PU8100. then, measure whether any pin of the five mentioned components is shorted to GND or not. then check whether any two pins of PU8100 are shorted together or not. make sure you have replaced PQ8100, PQ8101, PQ8102, PQ8103, and PU8100 all before plugging the power adapter in. I mean: do not plug the power adapter in, after replacing just some of the five components.
After these measurements, plug the power adapter in and unplug it after just 1 second. then check whether any IC has got hot. If not so, plug the power adapter again and unplug it after just 3 seconds. then check whether any IC has got hot. If any IC feels hot, do not plug it in again and let us discuss it.

[tibimakai]

Re: Asus Q502L does not boot up properly

So, just check with the Ohm meter for shorts for now.

[caspian]

Re: Asus Q502L does not boot up properly

that is right. If you are not good at soldering, first watch some youtube videos to learn how to do it carefully.

[tibimakai]

Re: Asus Q502L does not boot up properly

OK, finally I have all five parts soldered in.
I'm measuring for short, at these 5 parts and sometimes I measure short, for example pin #8 of the PU8100 and a minute later, the short is gone.
The FET switches?

[caspian]

Re: Asus Q502L does not boot up properly

do not connect any power to this mainboard as long as the shorts are not gone.

[caspian]

Re: Asus Q502L does not boot up properly

when measuring do not connect the red probe to any where, just connect it to pin #8 of the PU8100 while the black probe is connected to GND. then if it is not shorted, it is fine.

[tibimakai]

Re: Asus Q502L does not boot up properly

At pin #8, I'm getting 0.0035V, with the power adapter plugged in and did not press the power button. Nothing is getting hot.
Not much is going on, at this IC. At pin #12 I have 19.6V.

[tibimakai]

Re: Asus Q502L does not boot up properly

Since I have seen that nothing was happening, I have went over my soldering on the four FETs and the PU8100 and now, I have some voltages slowly building up, but it's hot again.
I'm quitting on this.
I don't have a scope, I don't have the right soldering tips and skills and I don't trust my soldering job. I don't see any short and it is still getting very hot.

[caspian]

Re: Asus Q502L does not boot up properly

if it is getting hot, do not connect the Ac adapter to the mainboard. now recheck to find shorted pins.

[tibimakai]

Re: Asus Q502L does not boot up properly

After a long period, I'm getting back to this.
Somebody soldered in the two copper wires for me(ripped traces repair).
There are no shorts at any of the PU8100 to ground, or between PU8100 pins, or any of the FETS.
Pin #8 starts around 1.9Mohm and starts dropping, but never goes to low.
All the PJPs are open except PJP8101 and PJP8100, that provides the 19.5V.
At pin #8 I should have 3.3V and at pin #18, I should have 5V, right?
It starts very low, like 0.035V and slowly creeps up, but PU8100 gets hot very fast. Same for pin #8 & 18.

[tibimakai]

Re: Asus Q502L does not boot up properly

I have replaced again PU8100, and tested all the pins of PU8100 to ground and between each other, than to ground. Only pin #4, shows 2 ohm. Everything else, shows values of kohms or mohms.
All PQ8100, PQ8101, PQ8102, PQ8103 show as expected, no short.
I have tested all the capacitors, to ground and none of them conduct at both sides, only at pin #4, of PU8100 shows that there is a short(2 ohm). I was told here, that is normal.
PJP8101 and PJP8100 are joint only. From previous steps, I have left them open.
PU8100, is still getting hot and voltages are missing.
It would be wise, to remove all four FETs and try it out that way?

[shotthruthemb]

Re: Asus Q502L does not boot up properly

I am beginning work on a faulty Q302L quad(above 1.9GHz I believe) with built in ram and I want you to know this post is very inspirational to me. Please keep at this I am learning from your processes and posts, I hope you fix this best of luck, hope to see what the problem is. I'm no expert but some thoughts came to mind... Is the power source adapter outputting correct volts? That's terribly unlikely but just a random thought. Is something sending to much power to your FETs and causing them to short the PU8100? Sounds like so many more iterations to test but it must be somewhere.

[tibimakai]

Re: Asus Q502L does not boot up properly

I haven't given up, I just did not get help and had other electronics to repair.
In the beginning I had most of the voltages(maybe even all of them).
I messed up with the LVDS cable, it shorted out and since then, the voltages are gone.
Replaced PU8100 and the FETs but does not seem to fix my problem. Something must be shorted, but I don't know which component.
This is only the second time, trying to repair a laptop. First time soldering QFN IC.
Also, it is very hard without schematics.

[SMDFlea]

Re: Asus Q502L does not boot up properly

"I haven't given up, I just did not get help and had other electronics to repair."

You have had lots of help.It takes time to go back through an old thread and try to get a clear picture of the tests done and results.Don`t give up on it !

[piernov]

Re: Asus Q502L does not boot up properly

@shotthruthemb you should open a new topic if you need help or if you want to expose your troubleshooting steps (always helpful to others)

@tibimakai didn't read the whole thread so sorry if I missed something. On PU8100 first thing to check is the voltage on the LDO outputs, pin 3 (VREG3) and pin 13 (VREG5).
If PU8100 is getting hot, either one of the previous pins may be shorted to ground or the chip is bad/improperly soldered.
Also pin 4 should not be shorted to ground, so this may point to bad chip/soldering. Check the solder joints under the microscope and make sure the chip sits flat on the board.

[tibimakai]

Re: Asus Q502L does not boot up properly

SMDFlea you are right, but I did not have a scope until now (from Santa) and I have to wait, until parts arrive from Ali.
Now, I'm in the same situation. I have run out of 1285A IC.
I have just removed the one, that was heating up.
I did not see anything wrong, with my soldering. It was a bit shifted, but it was still making good contact.
I have measured all the components, around PU8100 and all the FETs, capacitors and resistors, everything looks good. Only C6627 did not show anything.
I will place an order for 1285A and again the we will have to wait. I believe it will be the Chinese new year. Hopefully, I will get it until now.
Piernov, at pin #3 I was getting, something like 0.3V very slowly it was increasing. Same goes for Pin #13, it was 0.157V and slowly it was increasing. PU8100 was getting hot.