BQ24735 - faulty?

[Jane]

Re: BQ24735 - faulty?

Thank you for your replies
@mon2
There is not blob. JP 8805 is as a path on PCB. I would have to cut the path on PCB to divide JP8805.
Tomorrow I will check the surroundings of Q8805.
Yes, I have a variable power supply. How to use it in the best way in this case properly?

Sephir0th:
what current should I use if injecting voltage? Voltage 19V?

Thank you for help

[mon2]

Re: BQ24735 - faulty?

what current should I use if injecting voltage? Voltage 19V?

Never this high a voltage!! Always recommend to use a voltage lower or equal to the lowest voltage on the logic board.

We use 0v7 = 0.7 volts with our SHORT KILLER tool which can pulse out 30A of current. It worked to fix a macbook yesterday within minutes of being dropped off to our shop. With a thermal camera, lit up the tantalum cap like a Christmas tree. Could smell the defective cap which cracked up like popcorn.

Still suggest to review the board and use injection as a last resort.

What is the exact resistance to ground in ohms ? Use the lowest scale on your meter. Very possible that you have a shorted cap but we still need to keep the voltage LOW - in case that the same voltage travels to the CPU rail due to a defective high side mosfet that may be leaking. That is, what you apply here will reach the CPU and absolutely kill the component.

[Jane]

Re: BQ24735 - faulty?

There is 1.3 Ohm short to ground

We use 0v7 = 0.7 volts with our SHORT KILLER tool which can pulse out 30A of current.

Do you mean I should use 0.7V and as many Amps I can set on my laboratory power supply until those 30Apms?
I also tried to find out and check Q8804 as you suggested yesterday. Unfortunatelly I do not have a boardview and PCB is not described well - marking each part - so it is quite hard to find out a particular part. But if there were any short in cappacitors around that Q8804 also a drain of that Q8804 woud have to be in short, I think
But there is no other mosfet( I find) that is in short - except Q8802 ( after not being able to desolder JP 8805 because it is connected as a path on PCB.)

Is it a time for voltage injection now?
Thank you for help

[mon2]

Re: BQ24735 - faulty?

Can you post a few pics of your board?

The mosfets should be simple to locate. We know the gate pins are driven by the charger IC. Place your meter in DIODE mode. Remove all power to the logic board.

Short the meter probes and confirm the tone.

Now one probe on gate pin #4 as an example. Other meter probe to a nearby resistor. Do you hear a tone? No? Skip to another resistor till you do.

After finding the resistor, switch to the other side of the resistor. Other meter probe now direct to the charger IC.

[Jane]

Re: BQ24735 - faulty?

Here are some pictures of mainboard.
Both top and bottom sides have two pictures
Part1-a.jpg shows part where BQ24735 is and Part1-b.jpg is the opposite side where mosfets are.
Part1-b.jpg is the other part of side where BQ24735 is and Part2-b.jpg is the other part where mosfets are .
IN red ink I made few notes there
Thank you for advice how to continue with the repair.

[Jane]

BQ24735 - still probem with it

I try to repair laptop ACER SWIFT SF314-51 , which is dead.
I found out there is a problem with BQ24735 - ACDRV (pin 4) is only about 0.9V. ( if i remove resistor - coming from that ACDRV to mosfet, value is still not good).

Few others values of BQ24735 are:
Values are about :

pin 20: VCC 19V

pin 6: ACDET 2.6V

pin 16: REGN 5.99V

pin 5: ACOK 1.6V

When I remove pull up resistor from pin 5 ( ACOK) value becomes about 3.3V.

Do you think that there must be a problem after that pull up resistor rail, so that the voltage from ACOK is pull down not pull up?

I tried 3 different BQ24735 but the results still not good

Laptop schematic included.

Any help would be appreciated.

[mon2]

Re: BQ24735 - still probem with it

Leave the ACDRV resistor off till the voltage is boosted.

Apply flux and reflow the charger IC till the ic swims back into the proper alignment on the smd pads. Then gently push from the corner with tweezers till the ic moves away a small amount and let go. All while blowing with hot air. The ic will bounce back, naturally. The pads are likely shorting under the charger IC.

Check the ACDRV pin voltage again. Other voltages are fine. ACOK is open drain and requires a pull up resistor to define the logic high status. For now, review the ACDRV pin.

[Repairman851]

Hi Jane,
It is an old post but I have the same problem today. It is another Acer mobo but uses the same BQ24735 power controller IC. Wd you be so kind and reply if you did find the cause of the problem and remedies, if any.. Rgds

[Jane]

As far as I remember I did NOT solve the problem.

[rumpumpel1]

a comment about measuring AC-DRV: this is a PWM signal. Depending upon the duty cycle a multimeter will show much less, than the effective voltage. If you want to check AC_DRV use an oscilloscope.

[Jane]

It might be an interesting point about PWM, but how much different the value will be ( if using multimeter)?

[mon2]

If still stuck, carefully measure each pin on this BQ charger IC and post in a table with their pin # + pin labels.

The ACDRV must be a boosted value of ~25v as long as the conditions for the BQ charger IC are met. This includes CMSRC; REGN; VCC to this charger IC; ACDET.

ACDRV voltage = adapter voltage + REGN if the above conditions are met.

[rumpumpel1]

It might be an interesting point about PWM, but how much different the value will be ( if using multimeter)?

example: if there is no battery a duty cycle of 50% might be sufficient and a multimeter shows roughly 12V for ACDRV.

[ndarjo21]

If still stuck, carefully measure each pin on this BQ charger IC and post in a table with their pin # + pin labels.

The ACDRV must be a boosted value of ~25v as long as the conditions for the BQ charger IC are met. This includes CMSRC; REGN; VCC to this charger IC; ACDET.

ACDRV voltage = adapter voltage + REGN if the above conditions are met.

hi mon2, if VCC 18.8v, ACDET 2.8v, but the REGN is 12.2v, and AC drive is 0v. no shorted in the each pin of the IC except ground. is that normal? the REGN? BTST is 12.39v. the diode between BTST and REGN is normal.

[mon2]

No, not normal. REGN is a ldo output and should be ~6v. Remove for now the series 4k ohm resistor at the output of acdrv. Do not lose this part. Confirm that the BQ ic regn pin is not shorted to another pin on the device. Flux and reflow the BQ part if necessary with low air pressure to avoid loss of tiny parts. The BQ chip may be defective.

[ndarjo21]

thanks mon2