Acer Swift 5 (SF514-52T) reboot loop mistery

[nocnoc]

Hi all,

I'm quite new to this and trying to learn by help a friend with his SF514-52T that stopped booting after battery was replaced. I suspected the battery was bad but the problem persisted when putting back the original one (which is was still working although with reduced capacity).

When pressing the power-on button the symptoms are:
- Keyboard backlight and blue power LED turn on for about 5-7 seconds, and then flash off-on in ~3 seconds cycles (reboot loop).
- Display does not seem to turn on, although it sometimes seems to flash in between reboots.
- No other activity detected (fx. CPU fan does not turn on, etc.)

I have tried:
- Swapping back to the original battery which worked => same symptoms
- Powering on with disconnected battery => same symptoms
- Leaving the battery to charge which seems to work, charging LED switches from orange to blue when done and I can measure 8.6V on the battery connector
- Visually inspecting the board => all looks ok
- Checking AC input in charging circuit => all looks ok

Not sure where to go next, maybe something with the BIOS. Any suggestions or similar experiences?

[mon2]

Carefully measure the voltage to ground of each pin on the battery connector. Post each measurement.

[nocnoc]

I measured several times and get this:

PIN 1 => 8.68V
PIN 2 => 8.68V
PIN 3 => 0.00V
PIN 4 => 0.29V
PIN 5 => 3.28V
PIN 6 => 0.00V
PIN 7 => 0.00V
PIN 8 => 0.00V

Detail: Measured with the charger cable unplugged

I understand it corresponds to this if I have the right schematics:



Note: Schematics found in: https://www.badcaps.net/forum/troubl...9-1m-schematic

[mon2]

PIN 5 => 3.28V
PIN 6 => 0.00V

Pin # 6 is of concern. Each of these SMBUS lines should be ~3v3.

Remove all power. Meter in DIODE mode. Short your meter probes and you should hear a tone beep. Red meter probe to ground (yes red) - shield is ok on the logic board. Black meter probe onto pin #5 of this same battery connector (disconnect this battery during these tests). What is the measurement? This is a good measurement since this line is able to park @ 3v3.

Now repeat the same testing for pin # 6 (faulty?) line. What is the DIODE mode measurement?

[nocnoc]

I am sorry, I just redid the measurements to confirm and make sure: PIN 6 shows 3.28V and not 0.00V as previously stated.

Just in case, I also did the DIODE mode measurements (with red probe on ground) with charger and battery disconnected:
PIN 5 => 0.60V
PIN 6 => 0.55V

[mon2]

No fault then on the SMBUS lines. Diode readings are good for these lines.

Remove all power. Measure the resistance to ground of PLB1 (either side of this inductor). We are checking if there is a shorted component on the main power rail = excessive current draw will be sensed and then will halt the power by turning OFF the DCin mosfets.

Like the above, still with no power -> continue to measure the resistance to ground of each and every inductor onboard (usually are grey in color). Checking for shorted downstream parts.

Post details of any suspects.

[nocnoc]

I'm unsure which one is PLB1, I cannot locate it on the schematics. I will try my best to measure resistance of every inductor I can find.

In the meantime, here are pictures from the board in case you can see something.

[nocnoc]

I measured the resistance to ground of all inductors I could find (at least the bigger grey ones). Not sure which one is PLB1.

None seem to indicate a short, I get quite a big range of values however: ~7.5 ohm, ~30 ohm, ~500 ohm, or others increasing forever (from k to M to ...) and confusing my cheap multimeter.

[nocnoc]

Hi again,

I still have not found anything suspicious yet, I will try to learn more and follow the charging circuit troubleshooting guide once more to hopefully catch something.

I am still puzzled in what could be the reason for the battery charging to still work, and that it actually seems to boot for a few seconds (keyboard lights up for 3-5 seconds and display even flashes for an instant) before shutting down and rebooting.

I thought at some point it could be some "open case" detection protection (switch of some sort) that would halt on early boot but could not find any such thing.

Any theories as to what could cause such a behavior are welcome! The trigger was a battery replacement and apparently the new battery is good.

Thanks in advance!