Toshiba P855 only works with battery

[mon2]

Re: Toshiba P855 only works with battery

Ok. So the battery is charging? Is there a fault?

Does the unit operate with only the adapter?

[zioricci]

Re: Toshiba P855 only works with battery

Ok. So the battery is charging? Is there a fault?

Does the unit operate with only the adapter?

on the contrary, as I wrote in the title, it only works with the battery and not with the adapter

[zioricci]

Re: Toshiba P855 only works with battery

While hunting for shorts in the vicinity of the IC charger, I found this capacitor circled in green on the figure with a resistance of 0.4 Ohm...maybe a little low in value. Could this value explain the exclusion of the adapter as a power source?

[mon2]

Re: Toshiba P855 only works with battery

It is ok since you are measuring the resistance of pr225 which is a low value current sense resistor.

[zioricci]

Re: Toshiba P855 only works with battery

I read @Piernov's trhead, very interesting and as he suggests I also measured the resistance connected to the CMSRC output and it's ok, the mosfets are all ok... as an electronics hobbyist though to think that the adapter doesn't deliver enough current but I tried 3 of them and the current comes out in abundance.
Is there something that prevents the adapter from not having priority when connected together with the battery.

[mon2]

Re: Toshiba P855 only works with battery

Remove all power. Meter in lowest resistance scale.

Measure the resistance between the ACP and ACN pins directly at the charger IC. This is important to measure at the pins of the IC.

Post the reading.

[zioricci]

Re: Toshiba P855 only works with battery

it is not stable, it fluctuates between 2.5 and 6 Ohm

[mon2]

Re: Toshiba P855 only works with battery

Post a close picture of this area. This is of concern.

Still with no power, measure the resistance from ACP pin to the one side of the current sense resistor. Is it stable?

Should be ~0 ohms and stable.

Repeat to test the pcb trace resistance from ACN to the other side of the current sense resistor. Same expected reading.

[zioricci]

Re: Toshiba P855 only works with battery

0.5 the first and 0.6 the second. Both stable.

But I realized that I have not removed the RTC cmos, does it change anything?

[zioricci]

Re: Toshiba P855 only works with battery

I enclose pictures of the internal BQ24725 taken from the datasheet

[mon2]

Re: Toshiba P855 only works with battery

Remove the noted battery and test again. I do not believe it should change this measurement.

So to confirm, the reading that is not stable is when testing across the current sense resistor?

Test the resistance directly at the current sense resistor as well. Is it stable?

It is rare for current sense resistors to fail but that may be the issue for this case. Any sign of corrosion / liquid damage in this area?

You can try to flux and reflow this part but be careful to not apply heat to the LCD display. Often this resistor is under 1 ohm.

[zioricci]

Re: Toshiba P855 only works with battery

Correction, before I measured wrong maybe the tip didn't touch well and was unstable, now I'm sure that between pin 1 ACN and 2 ACP there are 0.8 Ohm stable

These 2 pins correspond to the two sides of the sensing resistance, if I measure directly on this resistor I find 0.2 Ohm, probably the extra 0.6 more will be due to the traces (?)

[zioricci]

Re: Toshiba P855 only works with battery

Post a close picture of this area. This is of concern.

pcb photo

[zioricci]

Re: Toshiba P855 only works with battery

the PD202 zener diode that looks like it burst works, it's just dirty

[mon2]

Re: Toshiba P855 only works with battery

Is PD202 with a chipped topside ?

Concerned about why there is a voltage @ BQ24725_LX when the battery is removed.

With the battery removed, PQ201 & PQ202 should be OFF so expecting 0v @ BQ24725_LX.

Suggest to remove PQ201 off the logic board.

[zioricci]

Re: Toshiba P855 only works with battery

Is PD202 with a chipped topside ?

it wasn't chipped, a little flux a little more

Concerned about why there is a voltage @ BQ24725_LX when the battery is removed.

What voltage, at what point of BQ24 ?

With the battery removed, PQ201 & PQ202 should be OFF so expecting 0v @ BQ24725_LX.

on the gates of the mosfet ?

Suggest to remove PQ201 off the logic board.

this operation worries me because I have already tried to remove some mosfets with hot air but I didn't want to insist because it seemed to me that too much time had passed and it would not come off-

But by measuring I see that PQ201 with the red lead on the source and the black lead on the drain is open and on the contrary I have the threshold voltage of 0.51 V, can it be deceiving?

[mon2]

Re: Toshiba P855 only works with battery

See attached. The voltage @ PHASE pin #19 to me is of concern.

This is the voltage created by both the high side mosfet (PQ201) and low side mosfet (PQ202) working together to lower the high adapter voltage that is fed into the drain pin cluster (5-6-7-8) of PQ201.

When the adapter only is connected I would not expect a voltage to be present on pin #19 that monitors the lower voltage.

For now, test the following ideas:

Remove the 0 ohm resistor @ PR217. This will remove the gate voltage on PQ201.

Then measure again the voltage to ground of BQ24725_LX. You can measure at the BATT+ battery connector pin. Do not have the battery connected.

What voltage do you read now ?

In summary, we want to disable PQ201 from the circuit.

[zioricci]

Re: Toshiba P855 only works with battery

ok i'll try now

[zioricci]

Re: Toshiba P855 only works with battery

When the adapter only is connected I would not expect a voltage to be present on pin #19 that monitors the lower voltage.

What voltage do you read now ?

In summary, we want to disable PQ201 from the circuit.

I wanted to let you know that having also the motherboard of the P850, identical to this one, also on this one the voltage is the same, that is 3.08 V, when there is only the adapter, the same also on pin 18 of BQ24725_LX

[mon2]

Re: Toshiba P855 only works with battery

Is the other motherboard a working board? If yes, it will help to troubleshoot this unit.

Same adapter works with the other motherboard?

You can measure the voltage to ground of each pin on the charger IC under the same conditions -> add the adapter & battery. Post the list.

Then let us compare the values from the known good motherboard against this one.

You mentioned earlier that you were attempting to remove a mosfet. Was it on this board?

Which one?