asus x451UA no ACOK

[brew99]

edit: title model# is wrong. Should be an Asus X541UA

I just want someone to let me know if I'm on the right track. I have this motherboard out of the laptop and running the AC adapter into it. It has a BQ24780S charge controller, which I believe is getting all the correct signals to initiate ACOK, but it is not going high.

BQ24780S:

VCC - 19V
REGN - 6V
ACDET - 2.6V
ACOK - 0V (otherside of pull-up res. has 19V, and res. measures OK at 1k)

Both FETS have 0V at the gate, so not turning on.

I've ordered a BQ24780S, but is there something else I should check?

This board works from battery only, not from adapter.

[on/off]

Re: asus x451UA no ACOK

Double check your reading.

acok resistor pull up usually only from 3V.

[brew99]

Re: asus x451UA no ACOK

OK double checked and you are right. Other side of resistor is 0V. I don't have +3VA being developed because there is no AC_BAT_SYS, but that's because the ACOK signal is not present. I injected 19V on AC_BAT_SYS and it fires up, so I'm confident that its just the lack of ACOK that is inhibiting the 2 FET gates to turn on.

Is there anything else on the BQ24780S chip I should measure before I try replacing it? I have a spare board, but I think the same chip is faulty, so I may need to wait until my new BQ chip arrives (Aliexpress, so will be a while)

[ktmmotocross]

Re: asus x451UA no ACOK

inject acok signal but i think that bq is pproblem

[brew99]

Re: asus x451UA no ACOK

I changed the BQ24780S charging IC, but it was same fault. Finally tracked it down to a missing incorrect value resistor inline with the ACDRV signal, which I guess was preventing the ACOK from going high. Anyhow, I now have power available via the AC adapter, but It is not charging the battery. It runs from battery or adapter, but will not charge the battery.

Measurements on BQ24780S: with ACadapter and battery connected
Pin - Voltage
1 - 19V
2 - 19V
3 - 18.5V
4 - 24V
5 - 3V
6 - 2.6V
7 - 0V, 80mV on good board
8 - 0V, 80mV on good board
9 - 0V , 125mV on good board
10 - 5V
11 - 3.26V
12 - 3.26V
13 - 3.37V, 2V on good board
14 - 3.37V, 1.9V on good board
15 - 0V
16 - 3.37V
17 to 20 12.0V, 900mV on good board
21 - 1.17V
22 - gnd
23 - 0V
24 - 6.07V
25 - 11.72V
26 - 12.01V
27 - 12.01V
28 - 18.9V

It must be something with the circuit around the pins 17 - 20 as they are drastically different. The charging FETS measure fine.

What should I look at?

Am attaching the boardview and RG for this:

[brew99]

Re: asus x451UA no ACOK

added Signal names to Pins for easier reference: Sorry couldn't edit the original post

Pin - Voltage - name
1 - 19V - ACN
2 - 19V - ACP
3 - 18.5V - CMSRC
4 - 24V - ACDRV
5 - 3V - ACOK
6 - 2.6V - ACDET
7 - 0V, 80mV on good board - IADP
8 - 0V, 80mV on good board - IDCHG
9 - 0V , 125mV on good board - PMON
10 - 5V - PROCHOT (low)
11 - 3.26V - SDA
12 - 3.26V - SCL
13 - 3.37V, 2V on good board - CMPIN
14 - 3.37V, 1.9V on good board - CMPOUT
15 - 0V - BATPRES (low)
16 - 3.37V - TB_STAT (low)
17 to 20 12.0V, 900mV on good board - 17 - BATSRC, 18 - BATDRV, 19 - SRN, 20 - SRP
21 - 1.17V - ILIM
22 - gnd - GND
23 - 0V - LODRV
24 - 6.07V - REGN
25 - 11.72V - BTST
26 - 12.01V - HIDRV
27 - 12.01V - PHASE
28 - 18.9V - VCC

[khaahk]

Re: asus x451UA no ACOK

So pins 17,19,20 have 900mV on good board? Strange because it looks like they should have battery voltage. Pins 26 and 27 have same voltage - check for solder bridge on charger or high-side mosfet gate short.

[brew99]

Re: asus x451UA no ACOK

Thanks for the reply. I'll have to recheck those voltages. I've just read-up on how a synchronous boost circuit works, and think I have a better understanding, at least somewhat. Just started playing with laptop repairs a few month ago, so there is so much to learn.

So am I right in that the HIDRV signal should be boosted to somewhere around 24V to turn on the high side mosfet? Of course, I won't be able to see the voltage with just a DMM if its switching ON/OFF like it should. The PHASE signal should be more a constant voltage though right?

[khaahk]

Re: asus x451UA no ACOK

About HIDRV correct, on the PHASE pin there are also impulses which will be equalized after inductor (with the cooperation of capacitors). Your multimeter should show mean value instead of impulses.

[brew99]

Re: asus x451UA no ACOK

OK guys, I still need some help on this one. The board is currently working from AC or battery, but will not charge the battery. Windows shows it charging for about 10sec, then just says plugged in. If I remove board, the charge and power LEDs act the same as a known good board.

I have used diode mode on each pin of the BQ, and the measurements are the same as the good board. I've changed the HI and LOW FETS and also BATFET. There was nothing wrong with the FETS, but I was just trying things.

Pin 17 - 20 all have about 800mV on them (so no PWM action), and the good board shows 12.6V. This is with only the charger plugged in. It looks to me like I'm not getting the switching action of the FETS to generate the charge voltage.

Any suggestions on what to check or replace? Anything to check on the EC?

[piernov]

Re: asus x451UA no ACOK

Does the battery work?

[brew99]

Re: asus x451UA no ACOK

yes, battery works and charges with known good board. I'm using same adapter and battery to test between both good and bad board.

Good board outputs 12.6V (even without battery connected, only AC adapter in) at the coil, which is also at the source and gate of BATFET (FET is OFF therefore gate and source shorted together according to the BQ document). Bad board only has 800mV at these same locations. Drain is at adapter voltage 19.6V in both boards.

[khaahk]

Re: asus x451UA no ACOK

Strange i don't remember seeing that on any boards.

Good board outputs 12.6V (even without battery connected, only AC adapter in) at the coil

[piernov]

Re: asus x451UA no ACOK

I'd expect a low voltage (usually floating) on the battery rail when no battery connected, in a topology where the main power rail is taken after DC-in MOSFET and not from the battery rail. (may not always be the case though, depends on how the charger IC acts)
When battery is connected without AC adapter, you'd see battery voltage (10 to 12V or so with 3 cells).
When battery and AC adapter are connected you'd see battery voltage climbing up to charging voltage (from whatever the battery is at, let's say 10V, to 12.6V or so with 3 cells).

So, what do you measure in those 3 configurations?

[brew99]

Re: asus x451UA no ACOK

Did some more measurements and have attached results. I think one of the issues is that the ACFET/RBFET are not turning on when the adapter and battery are in (CMSRC and ACDRV not up in voltage). It does turn on if only the AC adapter is in, so that is weird. The other weird thing is the power and charge LEDs act the same between the good and bad board, which I would have thought shouldn't be the case.

Anyhow, I need to figure out why the input FETs are not turning on when the battery and ac adapter are in, but do if only the ac adapter. It appears that the BATFET doesn't turn off when the adapter is inserted as the BATDRV voltage is still 6V above BATSCR

Sorry about the attachment. It seems to want to rotate the image when its uploaded.

[khaahk]

Re: asus x451UA no ACOK

Things that seem out of order:
ACDET 3.2V - too high, it is a simple voltage divider - something not correct there - it's value does not depend on charger - check the resistors.

SDA & SCL should be pulled high to 3V, communication on the line does not pull the voltage so low.

[brew99]

Re: asus x451UA no ACOK

I think I transposed the values for ACDET and ACKOK. I'm almost certain that I have 2.7 on ACDET (@ work so can't check right now).

I do have 3.2V on data and clock on the bad board, but the good board shows mV (or I measured wrong), so not sure about that.

At this point I'm going to try replacing the BQ again and see what I get

[brew99]

Re: asus x451UA no ACOK

I'm still fighting with this board......It's now at a point where it works on Batt or AC adapter, but when both are active, I get no charging of the batt, and also the CPU is limited (multiplier drops to min x4, according to CPU-Z software). Also when only on batt., there is a hissing sound (kind of like a transformer whine).

One thing I have noticed is the BATDRV voltage is not +6V from the BATSRC (12V). It is only about 12.2V, when on Battery (assuming it is not fully turned on). I've changed the charging IC twice and BATFET, with the same results. 4.02Kohm res. from BATDRV checks ok. Assuming that the charge pump of the BATDRV is being pulled down and not allowing full +6V from the SRC.

Anyone have any idea at what to look at next?

I've attached the charging IC schematic.

[brew99]

Re: asus x451UA no ACOK

I finally got this thing to work!!! I apparently do not know how to properly solder a QFN IC, as I tried replacing the charger IC again (I've soldered/unsoldered this about 20 times), and this time it worked. Man, I'm learning so much about how this IC can cause so many different issues.

On to the next one (it has shorts in rails)

[khaahk]

Re: asus x451UA no ACOK

Learning through experience is sometimes time consuming.
Good microscope should be of help in these cases.
Good work!

I finally got this thing to work!!! I apparently do not know how to properly solder a QFN IC, as I tried replacing the charger IC again (I've soldered/unsoldered this about 20 times), and this time it worked. Man, I'm learning so much about how this IC can cause so many different issues.

On to the next one (it has shorts in rails)