acer aspire 4755 shorted

[PapaFi]

Hello, my acer laptop 4755 series shuts down its power adapter/charger. But the power adapter/charger is good. After unplugging and plugging to outlet, 19v is present. Upon inserting its dc plug to dc in of the laptop, adapter shuts down again, no 19v out put. Laptop seems shorted? Any idea is the what comp is the culprit? Can you give me schematic? 2 Mofets PU3802, Pu4001 is good. Isolate the HDD, DVD RoM, Memory still no luck. Help...Thanks in advance.

[piernov]

Re: acer aspire 4755 shorted

https://www.badcaps.net/forum/showpo...89&postcount=3

Short to ground on DC-in rail or B+ rail. Measure resistance to ground on PU3802 source and PU4001 source.

[PapaFi]

Re: acer aspire 4755 shorted

https://www.badcaps.net/forum/showpo...89&postcount=3

Short to ground on DC-in rail or B+ rail. Measure resistance to ground on PU3802 source and PU4001 source.

Pu3802 source to grnd is 45.27k. PU4001 source to grnd is 1.8ohms.
Input jack between positive and negative 301k.

[piernov]

Re: acer aspire 4755 shorted

Ok so there is indeed a short to ground on B+ (called AD+_TO_SYS on the schematics).

First remove CPU from the board, then to find the short you can inject 1V with lab PSU on PU4001 source.
Check if GPU or PCH die heat up first. If they don't, you can increase the voltage until you find the component that heats up.
If GPU/PCH heat up, stop injecting voltage, there's a shorted high-side MOSFET that supplies GPU/PCH.

[PapaFi]

Re: acer aspire 4755 shorted

Hello piernov, can you ssend me name of components to check? PU4001 source seems shorted to ground as per your advice. thanks

[PapaFi]

Re: acer aspire 4755 shorted

Hello, I dont have psu, but battery 1.5v, 3v and so on may work, right?
Can you point out the gpu/pch in the pic i sent...

[PapaFi]

Re: acer aspire 4755 shorted

Hello, i dont have psu but using battery from 1.5v, 3v... and so on will work, right? can you please correct the picture w/c is the gpu/pch? thanks.
And if i may, where is the shorted high side mosfet that supplies gpu/pch?

[PapaFi]

Re: acer aspire 4755 shorted

Already downloaded the schematic you sent. Can you tell what page in the file?
Find it hard to see the components.

[piernov]

Re: acer aspire 4755 shorted

You need an adjustable power supply with constant current mode.

[PapaFi]

Re: acer aspire 4755 shorted

Oh felt sad, i dont have that kind of psu. Can you indicate the high-side MOSFET that supplies GPU/PCH? For the mean time I'll try to check those mosfet since i dont have psu.
Thanks again.

[mcplslg123]

Re: acer aspire 4755 shorted

@Papafi, piernov didnt said that there is short on high side fet's. He said if gpu/pch heats up, then thre is likely short on those high side fets. So in your case the short can be anywhere on +19V rail.

Check all the fets in diode mode. If pin1 and 4 shows short very likely that fet is bad. If all fets are ok , then you need to remove caps which are showing short one by one unless the short goes. This way it will take a little longer but can be done. You only need a hot air gun and soldering iron as long as you have the skill to do it.

[PapaFi]

Re: acer aspire 4755 shorted

@mcplslg123, thanks very much for added help options. one more thing, can you correct the image og mb I sent to piernov. where is the gpu or pci in there?
Thanks again.

[mcplslg123]

Re: acer aspire 4755 shorted

yes, those markings are correct on the pic.

[PapaFi]

Re: acer aspire 4755 shorted

@mcplslg123 thanks very much. I labeled it right hehe...

[PapaFi]

Re: acer aspire 4755 shorted

@mcplslg123, piernov its been a while. tough times in t'shooting which compnt is shorted.
need more patience...

[mcplslg123]

Re: acer aspire 4755 shorted

It should not take more then an hour even with this method of removing components one by one unless short goes. Have you tried removing the caps one by one and measuring whether short has gone??

[PapaFi]

Re: acer aspire 4755 shorted

Hello @mcplslg123, yes but think i wasnt lucky enough to find out which cap haha. Lots of caps was in short as i beeped, but still its not the one. in your expert opinion, which cap you will removed first for starter... i dont want my mb exposed more to heat station.
May be you can guess it which cap. thanks...

[mcplslg123]

Re: acer aspire 4755 shorted

It cant be guessed but you can remove coils near to the caps and see if it still shows short. then remove them. caps which shows short but after removing coil dont show short anymore-you can spare them.

[zhang]

Re: acer aspire 4755 shorted

Pu3802 source to grnd is 45.27k. PU4001 source to grnd is 1.8ohms.
Input jack between positive and negative 301k.

buzz pu4001 ( source ) with all of the PL
if it is shorted to any of the PL
remove upper mosfet of that PL Rail and try again if the resistance seems normal

[PapaFi]

Re: acer aspire 4755 shorted

Hello @mcplslg123 thanks very much for another options to make for fast t'shooing.