Acer E1-531 la-7912p motherboard no 3.3v

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

ENTRIP 1 and 2 read 1.5v both. PQ21 has 3.3v on its base via PR80.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Just curious if anyone is still following this very old thread

[brew99]

Re: Acer E1-531 la-7912p motherboard no 3.3v

I just read it today, and learned quite a bit from the detailed descriptions on the circuits.

Did you get it fixed?

I have a similar issue with the first two FETs and the charge controller on an Asus board. Currently waiting for parts to be delivered.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Did you get it fixed?

No, unfortunately not. I'm still stuck where I last posted: everything seems to be alright, but I still get no standby voltages on either of the two 3.3v or 5v ALWP lines

I was going to try resoldering and even replacing the components again to see if that's the cause (like a bad solder joint somewhere), but I changed my workplace in the meantime and the project came to a halt. Now I decided to dig it back up since it's a fairly good laptop and I could sell it or even keep it for myself.

[ronelex]

Re: Acer E1-531 la-7912p motherboard no 3.3v

try replace the filter caps on both 5v and 3v coil

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

try replace the filter caps on both 5v and 3v coil

You think bad caps would be enough to cause complete failure of both lines ? Worth a shot I suppose...

[piernov]

Re: Acer E1-531 la-7912p motherboard no 3.3v

If MAINPWON (voltage on base of PQ21) is high, then it's not inhibiting the ENTRIP signals. Which mean that PU5 should be creating the power rails if I'm right.

Multiple things could be at fault on the 3V/5V regulator circuit here.
Check voltage on VIN, EN, VREG3, VREG5, VO1, VO2.
Measure resistance to ground on +5VALWP and +3VALWP.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

I believe I already checked all of those, including the two switching output rails, so my only idea left is that one of the 4 FETs or the IC itself is not soldered properly or is faulty...

[piernov]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Should I understand that VIN is 19V, EN is 3.3V, VREG3 is 3.3V, VREG5 is 5V, VO1 is 0V, VO2 is 0V. Also that +5VALWP and +3VALWP have resistance to ground in the kiloohms range?
Then yes, either the PU5 is bad or not soldered properly, or a random component is missing from the circuit. I'd tend to say it's the IC that's bad or not soldered properly though if the above statements are true and the original issue was on +5VALWP only.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Should I understand that VIN is 19V, EN is 3.3V, VREG3 is 3.3V, VREG5 is 5V, VO1 is 0V, VO2 is 0V. Also that +5VALWP and +3VALWP have resistance to ground in the kiloohms range?

Correct. I checked several times, but I shall do it again nonetheless just in case I missed something.
I ordered several ICs so I shall remove it and solder a new one in place just to rule it out. If it still doesn't work, which it most likely won't, I'll move on to the 4 FETs. It's all QFN so I can't check if there's bad soldering somewhere unfortunately

[piernov]

Re: Acer E1-531 la-7912p motherboard no 3.3v

The MOSFETs are unlikely to be the issue either since the original issue was on the 5V rail only, and the usual failure mode there is a short between drain and source. (not always the case though so… cannot say for sure it's one or the other)

Even with QFN by taking a close look you can mostly see if it's soldered properly. Better to have a microscope, but a good magnifier can do to check how the solder looks on the sides.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

the original issue was on the 5V rail only

I actually FORGOT what the original issue was I'll have to read through my posts, since I remember replacing all 4 FETs (two for each rail), but I think I mostly did it for due-diligence and not because there was a failed one on BOTH 3.3 AND 5v rails...

[on/off]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Have you compare it your board with High Res image?

Maybe there are any components was missing.

https://drive.google.com/drive/folde...2VjRjZDWWNkaUE

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

I shall have a look, though I doubt I dislodged anything by accident. Just realized I never actually posted any pics of my actual board, so that should be something worth doing just in case the eagle-eyed spot something I didn't...

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Ok, here we are back on this board. Comparing my board to the hi-res photo, I did notice a couple of caps missing (encircled in red). They are not present on my board because I think they were shorted and I pulled them off. According to the boardview which is sadly not 100% accurate, I think those are PC65 and PC66.

I tried closing in as much as possible on those joints on PU5 with my magnifying visor and some strong lighting, and it looks good to me...maybe not professional, but decent. Same on the 4 FETs...looks messy I know, but I checked with my meter and I do get continuity from the pads to the pins. The pins of the FETs stick out ever so slightly from underneath the device that I was able to, with some very sharp probes, touch the pin and not the pad. I'll probably try touching them up a tad nonetheless. Really sucks not having a scope - that would've instantly told me if PU5 is working...

Latest measurements on PU5 (CCW from pin 1):
ENTRIP 1= 1.735v
REF+TONSEL = 2v
ENTRIP 2 = 1.732v
VREG 3 (+3VLP) = 3.36v
EN = 3.82v
SKIPSEL (2VREF) = 2v
VIN = 20v (adapter voltage)
VREG5 = 4.48v (missing PC65 on line)
BOOT1 = 4.48v (0v after PC59)

All other pins cannot be measured with DMM due to lack of scope

Next step is replacing PU5 again

[piernov]

Re: Acer E1-531 la-7912p motherboard no 3.3v

4.5V seems a bit too low to me on VREG5. The PC65 capacitor is probably important there, output stabilization for the LDO I'd guess.

May be a good idea to put PC66 back as well as it seems like it's the only decoupling capacitor for VIN close to PU5.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Alrighty tighty. More to come: I took the gamble and replaced PU5. Using my bench supply limited to 1A just in case, I slowly increased the input voltage to 19v and observed the activity of the 5v and 3.3v rails. This time, much to my amazement, there was something there, but not enough: only around 0.4v on each. I measured around PU5 again and I was no longer getting B+ at all now - it was getting stuck at PQ9 (page 47) for some reason. PU4 which drives PQ9 appeared to be fine: it was getting its 19v on pin 20 via PD6 and nothing was drawing excess current either, yet no B+, so WTH ?!

I botched a piece of wire on B+ to bypass PQ9 and PQ10 entirely and again very slowly increased the voltage: the current increased to 1A rather quickly and PQ16 got hot - shorted...great >_> Removed it, short was gone. Just to make sure there's no short on the 3.3v rail itself which would make it pointless to carry on, I repeated the idea of botching a wire onto PC60 and slowly bringing the rail to its nominal 3.3v. Strangely, the current was approaching 1A rather quickly as I was increasing the volts, but then dropped off to 0.16A once I hit around 3v, so I suppose we can call this rail functional.

Nothing I can do now but install those two missing caps - perhaps noise on PU5 caused the breakdown of PQ18 ? :| I'll probably botch two ceramic ones with leads onto those pads....

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Would it be safe to assume that as long as the size of the ceramic cap matches the pads, its value should also be close to the original or is that bogus and should be measured ? It could be a long and tedious process to find replacements for those ceramic caps, since they're not marked and I'd have to keep removing and measuring ones off donor boards until I find the ones I need.

[Dannyx]

Re: Acer E1-531 la-7912p motherboard no 3.3v

Well, just in case someone is still watching this thread, just wanted to let you know it's all over: PCH (U33) is dead. It probably died when the last high-side FET (PQ16) shorted and sent full adapter voltage into the 3v rail which conveniently enough is tied to some pins of the PCH, so that was the end of that...

What I tried last time was installing those two missing caps and soldering a new PQ16. Same story: slowly raised the voltage to 19v and watched my current, but it never went up. When I checked the 3vALWP rail, PQ16 was already shorted D-S, although the resistance between 3vALWP and GND still read about 1-2kohms, so I didn't think there was a short there. PU5 also seemed dead with no voltage coming out of it AT ALL this time. I soldered a piece of wire directly on 3vALWP and tried feeding it 3v limited to 1a and the PCH was burning hot and caused the supply to current-limit, so it was far past dead. Just for the sake of it, I increased the current limit of my supply, which allowed the output to reach the 3v I had it set at, but the current was like 3a, 10w so a dead-short there and of course it got even hotter. I think it would've melted itself off the solder balls if I had let it run long enough !....and this would be standby ! ! So yeah, another failed laptop repair. Louis is so lucky that FETs don't seem to die in macbooks and kill stuff around them...

Another theory is that PU5 was not soldered correctly the second time around either, which is very possible, my tools and skills being rather limited and I just noticed that's the only thing keeping the gates of those transistors in check - no external pull-down resistors - so if that pin was floating because it wasn't reaching the IC, that could've easily triggered the high-side FET. At least I now have a practice board to practice my QFN soldering since it really sucks...

Cheers guys.

[c.daniel]

Re: Acer E1-531 la-7912p motherboard no 3.3v

.... either the PU5 ... not soldered properly

Thanks a lot piernov; that was the problem at my laptop.
Laptop was not doing anything; was completely dead. Customer said that in one morning, laptop gone dead, without any "help". After i resolder PU5, was all good.
Thanks again.