Acer 7736zg No power

[bollin]

I got an acer aspire 7736zg that is showing no signs of life. No Leds come on, only a ticking sound (one tick per second). I measured voltages, and found that there are 19.8 volts on the MOSFETs close to the dc jack, and also to the IC near the battery connector. There are two MOSFETs (FDS8884) near the battery IC, one had 19.8 volts on drain, gate & source were about 1.8 volts and dropping slowly. I checked the MOSFET and it showed a short between gate and source, so i replaced it, but still the same (but 0 volts on gate this time).

I found 3.3 volts on the power switch, and it went to zero when pressed. The ticking also seemed to disappear, but i didn´t it only ticks once every ten seconds when power switch is pressed.

The mobo is a Hannstar j mv-494-0 (all the numbers i could see)
p/n is 55.4FX01.581G

Does anyone have a schematic for this?

[dj_ricoh]

Re: Acer 7736zg No power

after you remove the mosfet did the short was on the mb to? check that !

[bollin]

Re: Acer 7736zg No power

The short was gone after replacement, so i guess thewhatever the problem is it caused the mosfet to short (but this is just my guess)

[mytomr]

Re: Acer 7736zg No power

The short was gone after replacement, so i guess thewhatever the problem is it caused the mosfet to short (but this is just my guess)

What is the function of defective MosFET on the circuit.(series pass or switching for DC-DC), if in series pass config does gate voltage present (usually it came from logic controller e.g. syscon normally hi for on and lo for off), but if use in DC-DC circuit as switching then check the oscillator IC it might be te culprit.. consult datasheet of the ic it may help you..

[bollin]

Re: Acer 7736zg No power

I must say, I don´t know. The FDS8884 is labeled U32 in the schematic (SI4800BDY-T1). To me it looks like it is used in series pass?

[bollin]

Re: Acer 7736zg No power

It seems as the 5v s5 is missing, so i will replace ISL62392hrtz.

[bollin]

Re: Acer 7736zg No power

The board is a jv71-mv with ddr3 memory.

[Francisco.s]

Re: Acer 7736zg No power

What is the function of defective MosFET on the circuit.(series pass or switching for DC-DC), if in series pass config does gate voltage present (usually it came from logic controller e.g. syscon normally hi for on and lo for off), but if use in DC-DC circuit as switching then check the oscillator IC it might be te culprit.. consult datasheet of the ic it may help you..

U32, U33 and L10 are part of a circuit called Buck converter. (circuit switching for DC-DC)

http://en.wikipedia.org/wiki/Buck_converter

Regards.

[spidey]

Re: Acer 7736zg No power

can you tell the current on standby (s5) ?

[bollin]

Re: Acer 7736zg No power

can you tell the current on standby (s5) ?

No, as i currently does not have the possibility to do so. A lab power supply with current limiter is under construction, though.

However, I was looking at the schematic, and i have some questions.
The power, standby and charging leds are all powered by the 5v_s5, and are controlled by the kbc through switching transistors. So, there should always be 5 volts present, when the power supply is connected, right? If there isn´t 5 volts, i should look at the 5v_s5 rail, otherwise it is the kbc that is the reason for the leds not turning on?

I am not saying that the problem is there, I am just asking to see if I understood it correctly.

I know for a fact that the 3v/5v VRM is bad (my mistake) and I have ordered a replacement, and I can´t do very much testing until I have got it replaced.

[spidey]

Re: Acer 7736zg No power

No, as i currently does not have the possibility to do so. A lab power supply with current limiter is under construction, though.

However, I was looking at the schematic, and i have some questions.
The power, standby and charging leds are all powered by the 5v_s5, and are controlled by the kbc through switching transistors. So, there should always be 5 volts present, when the power supply is connected, right? If there isn´t 5 volts, i should look at the 5v_s5 rail, otherwise it is the kbc that is the reason for the leds not turning on?

I am not saying that the problem is there, I am just asking to see if I understood it correctly.

I know for a fact that the 3v/5v VRM is bad (my mistake) and I have ordered a replacement, and I can´t do very much testing until I have got it replaced.

When the power supply is connected, you should have 5v and 3.3v. That is the first stage of power in laptops. right now i dont have the schematics for this mobo. But 2-3 hours later when i arrive home, i'll search it for you. But it is a bit difficult to solve the problems without current monitoring. if you will work on laptops, it is a must.

[spidey]

Re: Acer 7736zg No power

Also check rtc(must be at least 2.6v) and re-program the bios if you have 5v and 3.3v. if all didnt work, then you may replace kbc.

[bollin]

Re: Acer 7736zg No power

U32, U33 and L10 are part of a circuit called Buck converter. (circuit switching for DC-DC)

http://en.wikipedia.org/wiki/Buck_converter

Regards.

Then the 1.8 volt that I got is good, if I understand things correctly.

Thanks for all the help, I´m learning loads here, even if it doesn´t help in this particular case.

[Francisco.s]

Re: Acer 7736zg No power

Then the 1.8 volt that I got is good, if I understand things correctly.

Thanks for all the help, I´m learning loads here, even if it doesn´t help in this particular case.

What chip the 1.8 volts are related to?
I have a schematic, but don´t know if it is the same as yours.

[spidey]

Re: Acer 7736zg No power

What chip the 1.8 volts are related to?
I have a schematic, but don´t know if it is the same as yours.

Video chip, DDR2 memory, chipset north.

[Francisco.s]

Re: Acer 7736zg No power

Video chip, DDR2 memory, chipset north.

Then I think we have the same schematic, and as I can see mosfet U23 and U25 are controlled by U22, and thorough L26 we have the 1D8V_PWR, so I can´t understand the relationship with the ISL62392 and this circuit. ¿?
I'm lost somewhere.

[spidey]

Re: Acer 7736zg No power

can you upload the schematic?

[Francisco.s]

Re: Acer 7736zg No power

can you upload the schematic?

This is the schematic I have.

[spidey]

Re: Acer 7736zg No power

i'm a bit confused. if you have 1.8v u should have 5v and 3.3v also. And after you press the power button you can get 1.8v and the other secondary voltages. So did you measure L27 and L28 ? And can you tell me, you have 1.8v after pressing power button or before ?

[Francisco.s]

Re: Acer 7736zg No power

I'm also very confused, as @spidey says, something doesn't match.