Asus R702UA dead (missing voltage)

[alderick]

Re: Asus R702UA dead (missing voltage)

Can I order any brand of 0402 20k 1% resistor?

[Techtiger]

Re: Asus R702UA dead (missing voltage)

You can find it on a scrap bord

[alderick]

Re: Asus R702UA dead (missing voltage)

I replace the resistor with one I found on scrap board, 20K, but with that one the probleme remain the same :'( 0.5V on JRST2402 et board doesn't work.
What is wrong with that board? :/

[Techtiger]

Re: Asus R702UA dead (missing voltage)

I replace the resistor with one I found on scrap board, 20K, but with that one the probleme remain the same :'( 0.5V on JRST2402 et board doesn't work.
What is wrong with that board? :/

remove the cap with +0.5V next to resister and see if the voltage 3.3V is stable

[alderick]

Re: Asus R702UA dead (missing voltage)

cap remove, it works! The problem is too find same cap now :/

Edit : the cap is 0.6ohm, so shorted, that explain everything. But My PSU doesn't show a short when I did put some voltage on JRST2402, strange?

[alderick]

Re: Asus R702UA dead (missing voltage)

The laptop can live without that cap or same as the resistor I must replace it?

[Techtiger]

Re: Asus R702UA dead (missing voltage)

It can or replace it with a another one from a scrape bord

[alderick]

Re: Asus R702UA dead (missing voltage)

Ok thanks, I'll check if I find one.
Last question, sorry i'm annoying I know
Can you explain what's the job of RTC_RST# function and why it prevent others power supply to start?

Again big thanks to save that PC

[piernov]

Re: Asus R702UA dead (missing voltage)

The cap on RTCRST# is required, high chances of the PCH not initializing properly if it's missing.

[alderick]

Re: Asus R702UA dead (missing voltage)

Thank you for you advise, unfortunatly I didn't find a cap and gave back the laptop to my familly. I think they let me know fast if it fail to start properly.
Is it dangerous or just unstable?
Can you explain the function of RTCRST? (just for me being less noob)

[piernov]

Re: Asus R702UA dead (missing voltage)

RTCRST# resets the Real Time Clock inside the PCH when it's pulled low. It also has the side effect of triggering a "clear CMOS", ie. resetting BIOS settings to the default.
The PCH cannot work if its Real Time Clock is not working so RTCRST# always has to be high.
The resistor and the capacitor act as time delay and stabilisation for this signal when the machine first receive power (after AC adapter, main battery and coin cell battery were all removed). Without the capacitor, the reset signal can come up "too soon" and the PCH may try to initialize the Real Time Clock while the RTC power rail isn't stable yet, causing it to crash.

[alderick]

Re: Asus R702UA dead (missing voltage)

Thank you for that very good explaination.
Have nice day.

[vampy999]

Re: Asus R702UA dead (missing voltage)

Hi All.
i got question too board x556uv, the circle on picture below dont have voltage.
Can someone help?

[johnbeton]

Re: Asus R702UA dead (missing voltage)

Hello, I have the same board, with exactly the same problem. I measured the voltages and have the same results as alderick. I reprogrammed the bios, but the problem remains.
Do you have more info about the cap and resistor you jumped ?
I can find JRST2402 near the ram-slot, but I cannot seem to find this cap and resistor.
I can also not find a schematic or boardview to help

[alderick]

Re: Asus R702UA dead (missing voltage)

Hello,
I don't remember which side of the board that cap is but you can find it with multi meter in beep mode, one probe on JRST2402 (RTC_RST side not GND obviously) et try all caps around the SOC.

Reprogram bios is useless in that case, the only faulty thing was the cap, just find it and replace it.

[johnbeton]

Re: Asus R702UA dead (missing voltage)

thanks for your reply, I was trying this, but this way didn't find the cap, I will retry and check them all

[johnbeton]

Re: Asus R702UA dead (missing voltage)

Thanks a lot guys, thanks to this topic I did manage to solve the problem. I found the cap and replaced it with one from a scrap board.
In case someone else runs in to this problem, attached is an image of the cap that needed replacement.

[alderick]

Re: Asus R702UA dead (missing voltage)

Nice job, and thank you for the picture, I should have post one myself back in time.

Edit: if people ask about the value, it's something like MLCC 1uF 6.3v 10%