LA-C421P BQ24780S no ACDRV

[lazaro.089]

Hi! I have a Thinkpad LA-C421P with no power to the system. No boardview nor schematic available. When connected it draws only 9mA.

After checking for shorts on coils I found no shorts and only then I injected 20V to the Main 20V system line (After the sensor resistor). The Laptop boots up Ok so the problem is charger is not driving the first 2 N-Channel Mosfets.


Following Piernov's Guide https://www.badcaps.net/forum/showthread.php?t=90356 I found out BQ24780 has:

VCC -> 19.8V
REGN -> 6V
ACDET -> 2.65V
ACOK -> 3.3V

but CMSRC is -> 0V and ACDRV -> 0V too.


I checked both input N-Channel Mosfets. Both seems fine, but I replaced them anyways.

Still no CMRSC or ACDRV.
I changed BQ, same behavior.

I don't know what to check next.

[jasko_jacker]

Re: BQ24780S no ACDRV

Usually bq24780s works in conjunction with 3v 5v alw ic check it

[mon2]

Re: BQ24780S no ACDRV

Assuming that you have checked the passives (resistors) to these input mosfets from the charger IC?

Perhaps they are missing or damaged.

[lazaro.089]

Re: BQ24780S no ACDRV

Assuming that you have checked the passives (resistors) to these input mosfets from the charger IC?

Perhaps they are missing or damaged.

Yes both R3 and R4 are 4kohm and are connected fine between BQ and mofets' source and gate respectively.

bq24780s works in conjunction with 3v 5v alw ic check it

Haven't checked the IC yet. But I thought 3 & 5V IC worked with SYS voltage. Does it work with unfiltered R0 voltage?

(Using BQ's datasheet naming conventions here)

[Sephir0th]

Re: BQ24780S no ACDRV

Could be Just a dead Charging IC. I've Challenged this behaviour before.

[ktmmotocross]

Re: BQ24780S no ACDRV

why nobody reads datasheets?

CMSRC is input for charge pump

as CMSRC is gettting voltage right after Q1 by r4, the first to check is resistance of R4

[lazaro.089]

Re: BQ24780S no ACDRV

why nobody reads datasheets?

CMSRC is input for charge pump

as CMSRC is gettting voltage right after Q1 by r4, the first to check is resistance of R4

Resistance between CMSRC and source of q1 and q2 is OK =4kohm.

Could be Just a dead Charging IC. I've Challenged this behaviour before.

I've already changed the charging ic ��

[SMDFlea]

Re: LA-C421P BQ24780S no ACDRV

The LA-C422P has a similar layout. https://www.badcaps.net/forum/showthread.php?t=88885 .I read on one forum that SW1 was broken causing a problem.Tape it down,if the switch is working ok and check CMSRC and ACDRV again.

[Sametbey]

Re: LA-C421P BQ24780S no ACDRV

you changed the charging chip and MOSFETs, injected 19v (+19V_SYS ) into the output, and the result is the same. Have you checked the AD_ID entry in the DC_IN input socket? he can't quit when he's not.

and are the pins fully soldered after the chip change ?

[lazaro.089]

Re: LA-C421P BQ24780S no ACDRV

The LA-C422P has a similar layout. https://www.badcaps.net/forum/showthread.php?t=88885 .I read on one forum that SW1 was broken causing a problem.Tape it down,if the switch is working ok and check CMSRC and ACDRV again.

That was actually it!!! I can't believe it! Thank you SMDFlea!!

[rbvndonh]

Re: LA-C421P BQ24780S no ACDRV

I think in new BIOS SW1 switch is no longer considered to start laptop.
I have 3 L570 and no one have malfunction to start nor the button is switched or not.

[coltron]

Re: LA-C421P BQ24780S no ACDRV

The L560 appears visually similar and has the exact same sw1 switch near the cmos battery. (My L560 was dead from the first 19v mosfet).
The plastic leg of the switch was broken off (making it harder to spot). I decided to desolder the switch and bridge the contacts, but this did not bring the laptop to life, so unsoldered the bridge. Again the mosfet gate had no supply.

With no obvious shorts to find I took the plunge and bridged the first mosfet across source and drain. That did it, the green light came on and the laptop starts. ( The bridge across the mosfet has been removed and still starts?)

Not all good news though, the laptop won't post. an get the 1 33 1 beeps. The ram is a good stick of DDR3 120 but regardless of slot cleaning the beeps continue.

I couldn't find a schematic for the L560, but found the L570 which apart from being the next gen of processor and ddr4 is remarkably similar to the L560.

The beeps maybe due to another fault unrelated to the ram?, how can I tell?

maybe one of the 2 SW1 contacts needs to be bridged, but that doesn't seem to help nd cuts the power off.

Despite the beeps, the laptop will power on and stay powered on all day
?, nothing on screen, (power light on lid is lit) just no processor action i think?

Any views on a possible line of investigation?

[coltron]

Re: LA-C421P BQ24780S no ACDRV

Board view would help?

[rbvndonh]

Re: LA-C421P BQ24780S no ACDRV

You need to solder only two top pins of SW1 to get ACDRV.
Try this and let know.
Maybe BIOS require reflashing also?

There could be also some bad caps..

[rbvndonh]

Re: LA-C421P BQ24780S no ACDRV

Board view would help?

Do you have and can share boardview?

[rbvndonh]

Re: LA-C421P BQ24780S no ACDRV

Try to remove PD303

[pingaroon]

Re: LA-C421P BQ24780S no ACDRV

Thanks for the SW1 notes. Was stuck with the 20V not getting through first mosfet - resolved by taping down SW1 (bare board repair) and fixing corrupt bios.

[Sushi1808]

Re: LA-C421P BQ24780S no ACDRV

Schematics diagram for Lenovo ThinkPad L560 - AILL1/L2 LA-C421P REV1.0 is now available, hope someone finds it useful.
https://www.badcaps.net/forum/showth...41#post1228941

[Vesko356]

Re: LA-C421P BQ24780S no ACDRV

Schematics diagram for Lenovo ThinkPad L560 - AILL1/L2 LA-C421P REV1.0 is now available, hope someone finds it useful.

Thanks for trying to be helpful, but Schematic Requests section is here: https://www.badcaps.net/forum/forumdisplay.php?f=41
Find a matching topic at the Schematic Requests section (for example this one, or this one) and upload the file there, so the people searching for it can be able to find it.

Here is a tech sub forum, I have already transferred your reply here to the one of the threads I mentioned above, and I'll also leave your reply here, but keep in mind for the future.

[janpatirkckaram1992]

Re: LA-C421P BQ24780S no ACDRV

Thanks for the SW1 notes. Was stuck with the 20V not getting through first mosfet - resolved by taping down SW1 (bare board repair) and fixing corrupt bios.

did you just solder the 1st fet drain to source?