Acer 5535 no power

[Learn2Day]

Hi,

I have on bench a Acer 5535 that doesn't power on and has the TPS51125 chip heating up. I don't think the problem is the chip itself.
I have checked it and I get 19V Vin on pin 16, but I'm only getting 2.35V on VO1 (pin 24) instead of 5V, and get 0V in VO2 (pin 7) instead of 3.3V.
Talked to a friend and he asked me to check if resistance is higher than 10ohm from VO1/2 coils to ground. Resistance is around 170ohm on both coils so I assume that's not the issue..

What do you guys think? Should I remove the chip and check if voltages appear or should I check somewhere else before removing anything?

Help appreciated.

Thanks.

[sorinac]

Re: Acer 5535 no power

NEVER start the notebook without the tps51125 or any other smps chip because you risk sending full 19V on the 5.5v and 3.3v rails ending in blown chips all over the board (same mistake i did) beacuse the gates from the controled mosfets will not be connected to anything.

first thing check for shorts on respective mosfets : u24, u25, u48 and u49.
if they are ok then change the tps51125.

[atsio]

Re: Acer 5535 no power

Do you get these voltages before you press the power button or after?

[Learn2Day]

Re: Acer 5535 no power

Before and after pressing the power button..

Will try to check the mosfets mentioned, unfortunately most designations on board do not match the schematics, although schematics match, they're from a different version..

Thanks.

[bushie]

Re: Acer 5535 no power

change that TPS.

[atsio]

Re: Acer 5535 no power

You shouldn't get any voltage before you press the power button. You should just have 3.3 and 5v on pins 8 and 17 before you press the power button.
What are the voltage on the regulator before you press power button and after?

[Learn2Day]

Re: Acer 5535 no power

I get 1.3V on pin8 and 3.5V on pin 17 before power button. Voltages are not correct, the problem is before, right?

Please define regulator.. Where would you like me to measure?

Thanks.

[toni31]

Re: Acer 5535 no power

You should have the voltage that you say pin 24=5V & pin 7=3.3V with adapter in without pressing PBTN.

[Learn2Day]

Re: Acer 5535 no power

"u24, u25, u48 and u49" are not shorted.

[toni31]

Re: Acer 5535 no power

change that TPS.

i agree

[Learn2Day]

Re: Acer 5535 no power

I'm having difficulty soldering the TPS chip. It would be great if you help out with some tips.
https://www.badcaps.net/forum/showpo...4&postcount=12

Thanks.

[bushie]

Re: Acer 5535 no power

it'snot that difficult.as i see you watched some tutorials.thats good.if you think you can't get it soldered with only the hot air gun try solder each pad one by one.it wont take that long.solder paste is good but as a tip(if you will use hot air gun),change the solder with some lead solder if you have ,watch the solder on the pads to be relatively even and most important do not put much solder paste(flux) underneath the chip,it will bounce it off the position when it will melt and starts boiling under the chip.put some solder paste on the pads than wipe out the excess with your finger so that will remain very very little paste on top of the pads.verify it after so you dont have a shortcircuit .hope you get it right.succes.sry for my english.

[lezsimply]

Re: Acer 5535 no power

The first time i installed qfn like tps51125 it blew up, actually 2 times on 2 different laptops
I was using hotair station and I was having a hard time placing and realigning them.

After so many tries, I managed to be more confident about it. At first I make sure the pads are flat but with small amount of solder then a good solder flux. I use magnifying glass to solder 1 pin on both sides using soldering iron, once I confirmed that all pins are aligned that is when I use the hot air. make sure air flow will not blow the chip away