Acer Aspire E5-571G-52NH powers on, no picture. PCH_ENVDD goes off and on.

[sergio_av]

Hi, I'm unexperienced with troubleshooting and I'm not sure how to proceed with this laptop.
Motherboard is A5WAH LA-B991P I think, i5-5200U and nvidia 820m.

When I received the laptop, CMOS battery had 0V. I took it out and all the testing has been done without a CMOS battery and without the main battery plugged in, I haven't been able to see physical damage, burnt or missing components with a quick visual inspection, and no shorts were found.
Laptop charges the battery, powers on when ON button is pressed when powered from charger and when powered from the battery, but no picture.
When powered on, the backlight tries to turn ON and immediately turns OFF, but the frequency of this happening is different depending on which RAM slot is being used. Using left slot, it happens every second, while if I use the right slot, it happens every 6 seconds or so.

U8 has stable 3.3V IN, but both OUT and EN pins have 3.3V that goes OFF and then ON again (matching screen backlight coming ON and OFF).
Pins 1, 2 3 and 7 from U6, the bios chip, show the same behaviour, while BIOS CLK pin shows the opposite behaviour (when there's clock signal or voltage, the 3.3V from the other pins go away, or vice versa, I don't know which one causes the other to change.
Both PLT_RST and PLTRST_VGA have 3.3+V. They're not completely stable, it fluctuates between 3.30V and 3.34V.

CPU/Chipset without ram https://streamable.com/p3wx6g
RAM in left slot https://streamable.com/gcim6z
RAM in right slot https://streamable.com/zv1mvn

Link to Schematic & boardview - https://www.badcaps.net/forum/troubl...atic-boardview

Any help will be highly appreciated, I will upload an image with voltages and schematics + boardview that I found on this website and on youtube.

[sergio_av]

Sorry for the double post but I can't edit the post above anymore and I forgot to add that I can't see capslock LED turning ON and OFF when the key is pressed, but I don't know if it has one, and the fan spins faster, slower and stops spinning depending on temperature. Also there's no display output through HDMI.

[mcplslg123]

First verify that your motherboard is "Posting" or not. To do that,just plug a usb keyboard and press numlock key.
If its posting but no display then proceed to check lvds pin voltages.
However, i stongly feel that its not posting at all.

[sergio_av]

First verify that your motherboard is "Posting" or not. To do that,just plug a usb keyboard and press numlock key.
If its posting but no display then proceed to check lvds pin voltages.
However, i stongly feel that its not posting at all.

I'm getting no LED response from USB keyboard

[loopster]

Very likely a corrupt Bios. These machines were notorious for bricked Bioses. Try a Bios recovery USB (google, FN+Esc), or
desolder the chip and reflash with ch341a, for example. Fixed a few similar ones.
Maybe I can find the correct Bios.rom version somewhere on one of my machines which works 100% for recovery (not all do).

[sergio_av]

Very likely a corrupt Bios. These machines were notorious for bricked Bioses. Try a Bios recovery USB (google, FN+Esc), or
desolder the chip and reflash with ch341a, for example. Fixed a few similar ones.
Maybe I can find the correct Bios.rom version somewhere on one of my machines which works 100% for recovery (not all do).

I had in mind purchasing the BIOS programmer and, since I thought a corrupted BIOS could be an option for this laptop, I ordered it 4 days ago.It comes from aliexpress so it will take a week or two.
The BIOS I had in mind to test is the one from this post
https://www.badcaps.net/forum/troubl...63#post1007963

I will back up mine, test that one or the one you provide if you find it and will report back if the laptop is fixed or not.
I hope it's just that and I can revive the laptop.

[sergio_av]

I received the programmer and flashed this BIOS file as is https://www.badcaps.net/forum/troubl...63#post1007963, laptop didn't post and I lost 3.3V in the U8's EN pin, but it responded to power ON button.

Then I tried with this BIOS file https://www.badcaps.net/forum/troubl...71#post1457271 with clean ME and the DMI and Windows key edited from my BIOS, laptop stopped turning on and audio chip heats up a little (25c). There is 3.3V in power ON button, but not on U8's IN pins, +3V_SPI and +3VALW present, but +3VS is not present.

After that I tried without ME cleaned from previous BIOS file, and same result, no power ON anymore, I flashed the original BIOS back and still not powering ON