Lenovo Ideapad 110-14IBR - some power rails missing

[paulo66]

I´m only a self-taught hobbyist and I buy cheap broken stuff for practical lessons.

CG420 NM-A805 REV 1.0 https://www.badcaps.net/forum/attach...4&d=1591891792

Bought used "for parts or not working". I´ve got another in exact same condition, same problems, so it could be a recurring fault in these units.

Now this unit turns on and charges the battery, but that´s all it does. No image and no cpu activity. I doesn´t pass syson in the startup (power) sequence.

So I´ve got +19V, +11V, +3.3V and +5V from PU401 and PU402 and that´s it. No CPU core and no GFX core voltages.
Looking at the power diagram on page 50, PU1 (LV5075a) seems faulty. All the power rails from this chip are missing.
Just one thing remains puzzling: from PL1 (+1.05VALW) the resistance to ground is zero according to my DVM. I´ve since tried injecting DC and the bench PSU went up to +0.5V/3.26A, meaning about 0.15R. Which ever is right. My PSU delivers only 3Amps and I´m guessing the ground plane on the motherboard is sinking all the heat. No chance of finding a bad cap or RAM cell or any other possible culprit.

Any hunches? I´ve since resoldered PU1 and reflashed the BIOS to no avail.

[piernov]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

SoC warming up when injecting?

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

Yes it does, though from a certain coil, of which I don't remember the ref. ATM, sorry. I'm off to work. I'll post ASAP.

Thanks!

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

It's actually two. PL902 and PL903.
UC1 starts to warm up with voltages higher than +1V. So I guess these are good news.

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

PL902 (CPU): +1.5V/1.17A 5.8R
PL903 (GFX): +1.3V/2.18A 62R

Both measured with unit turned off. Charger and battery unplugged.

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

Update: redid the soldering on PU1. There´s now +1.8V on PL2. The SoC warms up, still no voltages at PL902 and PL903.

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

Well, I "unjumped" PJ502 and PJ503 (page 55) to isolate PL3 from the +1.35V path ahead, and measured resistances.
PL3 now measures 13R to ground.
The opposite side of the jumpers measure 0.1R. Looks like a dead short to ground.
This means the soldered RAM is busted, right?

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

The above was not a rethorical question :-) I´m a hobbyist eager to learn and would appreciate some guidance.

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

Rhetorical*

[paulo66]

Re: Lenovo Ideapad 110-14IBR - some power rails missing

Perhaps I should invest in a more powerful bench supply? If it gets to +0.5V 3A, then heat dissipation is only 1.5W. Also, if the voltage change per current draw is linear, then with 10A the voltage should rise to more or less +1.35V, I think.