[HELP] Acer AN515-55 (LA-J871P Rev: 1B) – Board won't power on after GPU investigation – Suspecting Super I/O or PCH

[Destroyer-Br]

[HELP] Acer AN515-55 (LA-J871P Rev: 1B) – Board won't power on after GPU investigation – Suspecting Super I/O or PCH

Hi everyone,

I'm working on an Acer Nitro 5 unit with the following specs:

• Motherboard: LA-J871P Rev: 1B
• Model: Acer AN515-55-59MT
• S/N: NHQ7JAL00403906A973400
• SNID: 03902728734

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Initial Issue


The laptop initially presented graphic issues and driver failure (Code 43) for the GPU.

After preventive maintenance (cleaning, thermal paste, etc.), it powered on normally. We disassembled it again to inspect the GPU, reassembled for testing—it worked. Disassembled once more to show the client the GPU condition, and on the final reassembly (with no physical damage or errors), the board completely stopped powering on.

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Findings So Far

• Super I/O was shorted. Replaced with a brand-new one (pre-programmed).
  → Short is gone, but the board still won't power on.
  → Power supply draws only 0.013A (13mA).
  → Pressing power button or shorting PWRBTN pads does nothing.
• ON/OFFBTN# line shows 3V, and when shorted manually (or using keyboard), logic state changes → Super I/O receives the signal, but no reaction afterward.
• Replaced Super I/O again, this time using one from a donor board (same model & revision). Perfect solder job, aligned, inspected under microscope → No change.

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Power Rails & Signals

• +3VALW is missing
  → Should be enabled by the Super I/O, but the EN signal is not generated.
• Replaced PCH (Platform Controller Hub) and reprogrammed BIOS chip with a clean firmware → Still no change.
• Verified:
  • 19V input present
  • +3VLP present (feeding Super I/O)
  • +5VALW present
  • PU301 replaced (no change)
  • +1.05VALW impedance OK
  • No shorts on CPU/GPU VRMs, audio, or network ICs
  • All components appear intact visually – no burns, no missing parts
  • Board is clean, no soldering accidents
• Tested by injecting voltage manually into +3VALW rail (with previous PCH)
  → PCH slightly warmed up
  → No abnormal consumption or heating elsewhere

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Current Status

• Board does not power on
• All major voltages present except for +3VALW, which depends on an EN signal from the Super I/O
• Super I/O receives power and ON/OFF signal but does not release EN to trigger power sequencing
• I've exhausted the typical troubleshooting steps and now I'm stuck.

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Request for Help


I strongly suspect the issue lies in the Super I/O logic or some missing condition it needs to allow the EN signal to be generated.

If anyone has experience with this board or similar behavior, what conditions must be met for the Super I/O to enable the +3VALW rail?

If you need voltage references or specific measurements, let me know—I'll provide whatever is needed.

Thanks in advance!

[Destroyer-Br]

Additional Info


Just to complement the information:

• No signs of low impedance, shorts, or high consumption around JPQ1, JPQ2, or after UQ2.
• I also tested by injecting 3.3V via PJ302 (with 19V present and the board switching 5V by itself).
  → The board draws 0.184A (184mA) in this condition.

Regarding the initial short on the Super I/O (which was the first component replaced):

• The short was located on the +3VLP line.
• After replacing the Super I/O, the impedance returned to normal, the short was gone, and the +3VLP rail came back as expected, as mentioned earlier.

[mcplslg123]

+3VALW will come up only after triggering the mb as per power sequence but EC_ON should be present in off condition(seems contradictory to me).

Have you checked RTC circuit? Main bios flashed?
Have you checked resistance to GND on switched rails like +3VS/5VS etc.(Pg 78)?

[Destroyer-Br]

+3VALW will come up only after triggering the mb as per power sequence but EC_ON should be present in off condition(seems contradictory to me).

Have you checked RTC circuit? Main bios flashed?
Have you checked resistance to GND on switched rails like +3VS/5VS etc.(Pg 78)?

My response:

Thank you for your comments. I think you may have misunderstood some parts of my explanation, so let me clarify:

1. +3VALW Sequence
   You're correct that +3VALW only appears once the board is triggered—so I did read the start‑up sequence properly.
2. EC_ON
   EC_ON is present even when the board is off. I confirmed this because I'm seeing +5VALWP generated by PU502, which receives 5V_EN via EC_ON directly from the SIO.
3. Main BIOS (UT5)
   Asking whether the main BIOS is “working” doesn't make sense in this context: if the board never reaches the start‑up sequence, you won't even see +3VALW at the EEPROM pin—so it can't possibly be operating.
4. Switched Rails (+3VS/ +5VS)
   I checked for low‑impedance shorts or unexpected current draw around JPQ1, JPQ2 and downstream of UQ2 and found none. Here are the measured resistances to ground after UQ1:
   • +5VS (after JPQ2): 3.78 kΩ
   • +3VS (after JPQ1): Rising infinitely on high‑ohm range until it eventually zeroes
5. RTC Circuit
   Everything looks fine here:
   • DH1: 3.21 V at pin 3 (+CHGRTC)
   • +VL_RTC (pin 1): 3.00 V
   • RTC battery pin (pin 2): 0 V with the coin cell removed; restores to ~3 V when installed
   • I also verified +3VL_RTC at the PCH side—across CH47/CH48 and RH99/RH98/RH51.

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Any other ideas on what I can test next?

[Destroyer-Br]

Just to clarify, the correct motherboard model is LA‑L181P, not LA‑J871P.

[Destroyer-Br]

up

[mcplslg123]

Your problem perhaps is classic acer thermal protection for SIO detailed on page 58 of LA-L181 schematic.
3V_EN_R is present?(I know 3V_EN is missing)

[Destroyer-Br]

[REPAIR REPORT] Motherboard with unstable power consumption – suspected faulty PCH or enabled Boot Guard

Hello fellow techs,

After a full day of troubleshooting, I've decided to call it quits on this board. I'm sharing all the steps and findings here — maybe it'll help someone else or spark new ideas.

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🛠️ Diagnosis and Repairs:

• Initially, the board was completely dead.
• I found PQ201 was leaking, which was disrupting the BI_GATE signal from Q1A/B, responsible for EC_RST#.
• After fixing that, I regained EC_RST# and MAINPWON, both at 3.3V.
• The board showed a blue LED, but the power draw stayed at just 0.02A.

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⚙️ Actions Taken:

• Replaced both PCH crystals YH1 and YH2.
• The board began powering on intermittently with consumption up to 0.70A, but would sometimes drop to 0.40A.
  • In these moments, only GPU and PCH warmed up.
  • The CPU VRM remained partially inactive.
• At times, it would revert to 0.02A again.

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🔍 Odd Behavior:

• Occasionally, depending on where I touched the board (no clear pattern), the current would spike to 1.3A or even 1.8A.
  • The CPU got very hot, and the PCH also heated up.
  • Still, no reset occurred — the board showed typical "no POST" behavior (power cycling without boot).
• Reflashed the BIOS, cleaned the board thoroughly, and reflowed many points — no improvement.
• I tested countless signals — too many to list here.

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📏 Notable Measurements:

• Signal H_PLTRST_CPU# was only 1V (resistance measured at 1108Ω).
  • Expected: close to 10KΩ.
• VR_ON signal present at 3.3V.
• PLT_RST# also had 3.3V.
• Unfortunately, I couldn't check the crystal clocks or SPI bus signals, as my oscilloscope can't handle those frequencies 😔.

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🧩 Final Status:

• I managed to get the board into S0 state.
• But from there, I couldn't progress any further.
• Suspicions:
  • Faulty PCH (possibly received a bad chip).
  • Possibility that the machine had Boot Guard enabled, and replacing the PCH broke the security key handshake, blocking communication.

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Thanks to everyone who followed and contributed during this repair attempt!
Unfortunately, this time I had to give up. Still, the experience was full of learning.

Cheers!