Acer Aspire 5 A514-55 - won't power on, no charger LED, battery not flat - usual suspects?

[DenK]

Dear all, I am trying to troubleshoot an Acer Aspire 5 A514-55 that won't power on. I'll describe the symptoms and my findings so far, and I would like to seek guidance and suggestions on possible suspects in terms of cause/component failure. My initial thoughts are battery charger IC and/or ideal diode/MOSFET (that switches between incoming DC and battery power), but I could be totally wrong on this.

1) Laptop was working fine on battery, then user realised battery was running low. Plugged in AC adapter but noticed it was not charging (LED on AC adapter plug did not light). Eventually shut down from low battery.

2) Since then does not power up, whether on AC adapter or battery.

3) Tried the following without success:-

a) battery reset switch - held for 60s

b) disconnect adapter, hold power button for 15s

c) left charging overnight

4) Findings so far (see image below):-

a) AC adapter works fine - tested using multimeter.

b) laptop DC jack connection to motherboard seems fine - measured 19.5V at points A, C, D. However, LED on AC adapter's DC plug does not light

c) I read that some Acer models have a pin that has to be grounded (B) to indicate DC plug is fully inserted, otherwise battery won't charge. This was confirmed to be fine here (that is, B was grounded when DC plug was inserted).

d) However, 0V in areas beyond (i.e. to the left of) the components in the red box

e) Voltage at battery positive connector: varies when AC adapter is plugged in, so far 16.5V and 17.3V have been measured (too high?) at different times. Without AC adapter plugged in, 14.8V.

f) Trying to power up the laptop by shorting the 1st 2 pins of the keyboard connector also does not work, which suggests not a power button issue

[piernov]

https://www.badcaps.net/forum/troubl...arging-circuit

[DenK]

https://www.badcaps.net/forum/troubl...arging-circuit

Thank you piernov! That is a detailed and educational post, and I'm still digesting it. I'll also head over to the schematics forum to see if anyone has the schematics for this laptop model and try to apply the troubleshooting steps you'd set out in the post!

[DenK]

So I removed the board and examined the underside. I found what looks like signs of a missing component. I could be wrong, but looking at the page linked to by piernov, could this component be the AC input current sense resistor? Judging by the "R" designation and large lands on the PCB.

[mon2]

Yes, you are on the right (pcb) track. Hunt around for the charger IC which will probably be the 'BQ' series. Share the pic of this IC. We can then review the datasheet or sample schematic to understand which pins are the ACN / ACP used for the adapter current sense pins.

Once these details are known, without power to the board, measure the resistance from ACP pin on the charger IC to PR254 right side pad. There should be ~0 ohm resistance in this path. This will confirm that the missing resistor is indeed the current sense resistor.

If available, you can also study the schematic for this logic board and confirm the value of PR254.

[DenK]

Thank you mon2!

I did find the battery charger/controller prviously, as I was preparing to go through the troubleshooting process in piernov's guide before I discovered this.

It's a BQ24800. Product page is here https://www.ti.com/product/BQ24800, but for some reason they only have a brief datasheet without the usual pinout chart - full datasheet upon request. I've attached a copy of the brief sheet for convenient reference, while I continue hunting for the full datasheet.

Edit: Ha! The datashet for the eval board for this controller was available, and in that datasheet was a schematic with a pinout. Attached!

I wonder if TI uses the same pinout for all its BQ2x controllers.

Edit: Seems like it, pins 1 and 2 are ACP / ACN just like the bq24781.

Unfortunately I don't have the schematic for this board, although I've put up a request on the relevant board. In the meantime, a related model - Acer Aspire A514-52 (which schematic was available) - uses a 0.01R 0805 1/2W ±1% current sense resistor. Wondering if I could use the same value.

Edit: From the BQ24800 EVM datasheet, the eval board uses a 0.01R resistor as well.

[mon2]

Yes, some parts, like some techs that learn and disappear with the fixes, are in the witness protection program.

However, we can learn what we want from the BQ24800 EVM schematics.

See attached.

[DenK]

On another note though, would a missing current sense resistor explain why the laptop won't power on even on battery power? (and battery measures around 14V+ so it doesn't seem flat)

[DenK]

Yes, some parts, like some techs that learn and disappear with the fixes, are in the witness protection program.

However, we can learn what we want from the BQ24800 EVM schematics.

See attached.

Thank you mon2! It looks like we arrived at the same solution and our messages crossed. 😀

[mon2]

Yes

Connect only the (charged) battery. Confirm the voltage to ground on the charger IC pin # 28 (Vcc). Need to confirm that this component is being powered or not.

[DenK]

Sooo... I did a quick test for continuity from pins 1 and 2 of the BQ24800 (per attached photo in case I got it wrong) to either pad of the missing component. No continuity

I might be doing something wrong, will try again tomorrow. I'm quite sure there must be something across those pads.

[DenK]

Yes

Connect only the (charged) battery. Confirm the voltage to ground on the charger IC pin # 28 (Vcc). Need to confirm that this component is being powered or not.

Thank you mon2, I will check that tomorrow and report back!

But as I mentioned in my initial post (item 4(e)), there's a positive voltage on the battery connector's +ve pins with no battery attached, only AC adapter

[alfredposadas09]

Thank you mon2, I will check that tomorrow and report back!

But as I mentioned in my initial post (item 4(e)), there's a positive voltage on the battery connector's +ve pins with no battery attached, only AC adapter

hello try to measure the vcc pin 28 if you got a 18.5v-19.5v, next to check is the pin 6 acdet you should have 2.6v and not should not exceed to 3.15v.. next check the regn pin 16 it should be 6v, then check acok you should have 3.3v sometimes some laptops doesnt use acok

pin 28
pin 6
pin 16
pin 5

[mon2]

re: post # 12

Ok but asking to connect only the battery. Disconnect the ac adapter. Testing if the charger IC receives its power ok on pin # 28 (Vcc).

[DenK]

re: post # 12

Ok but asking to connect only the battery. Disconnect the ac adapter. Testing if the charger IC receives its power ok on pin # 28 (Vcc).

Of course, certainly~ was just mentioning by the by

Brief updates:

1) Discovered battery had self-discharged to mV level in the last few days! So I'm unable to test on battery power now as well

2) Having said that, I confirmed there is continuity between the battery +ve connector pin on PCB and pin 28 (Vcc) of the charger IC, so if the battery was working, current should flow up until at least the pin.

3) I think I've figured out the actual AC current sense resistor. Pads connect to the charger IC's pins 1 and 2, it matches the value (0.01R) and typical package footprint (0805), and the layout next to the adjacent MOSFETs resembles closely the typical layouts for the BQ24xxx (schematic from piernov's post)




I believe "B" = 1st DC-IN MOSFET, "C" = 2nd DC-IN MOSFET, "D" = AC sense resistor... but not sure what MOSFET "A" is.

Which means the missing PR254 is still a mystery.

4) I received a reply on the schematics and boardview request, but I was informed only 1 or the other could be shared, and I got the boardview 😅

5) alfredposadas09 Thank you for your suggestions! I didn't bring the AC adapter with me, so I will do that at home and post my findings. Also need my li'l microscope for this ...

[DenK]

Hi alfredposadas09, I've finally managed to get the measurements you asked me to check. I tested with AC and on battery, and the numbers are "AC / Battery":-

1) pin 28 (Vcc): 19.0V / 16.0V (Battery voltage also 16V)
2) pin 6 (ACDET): 2.63V / 12mV
3) pin 16 (BST_STAT): 0.6V (did you mean 6 or 0.6?) / 380mV
4) pin 5 (ACOK): 3.3V / 0V

As an aside, I measured 19.0V on both sides of the missing PR254... it's a 0805 SMD component, based on the size of the hole in the solder, and I'm wondering if I should try shunting it with a 0.01R AC current sense resistor and see if that works...

[mon2]

Sorry, my bad, interested to confirm REGN pin #24. This pin should be 6v to ground when the adapter is used.

ACDRV (pin #4) should be ~25v to enable the dcin mosfets when the adapter is used.

[DenK]

Sorry, my bad, interested to confirm REGN pin #24. This pin should be 6v to ground when the adapter is used.

ACDRV (pin #4) should be ~25v to enable the dcin mosfets when the adapter is used.

No problem at all, happy to provide whatever info I can 😄

1) pin 24 (REGN): 6V
2) pin 25 (BTST): 5.7V

(ok I misread your post, missed out pin 4 - will do that soonest!)

[DenK]

On a whim I measured the resistance of (what I believe to be) the AC current sense resistor (see post #15, PRB3). To my surprise, it measured 1R (not 0.01R as I was expectng). Taking a closer look at the component it appears that it is indeed supposed to be a 1R resistor. In which case I wonder if it still could be the AC sense resistor?

[DenK]

No problem at all, happy to provide whatever info I can 😄

1) pin 24 (REGN): 6V
2) pin 25 (BTST): 5.7V

(ok I misread your post, missed out pin 4 - will do that soonest!)

Pin 4 (ACDRV): 25V

Knowing now that ACDRV drives the DC-IN MOSFETS, I then measured the gate voltage of those FETS.



MOSFET A: 17.4V
MOSFET B: 25V
MOSFET C: 25V

Which suggests that B and C are indeed the DC-in MOSFETS. Curiously, I was now able to detect 19V all the way up to point E - that is, past the AC current sense resistor! Previously there was no voltage passing through the MOSFETS 🤦