IdeaPad s500 Touch sorted

[John_F_L]

Hello everyone,
I have an Ideapad S500 touch which is not powering on.
In the beginning I thought there was a problem with the TPS51225 controller which was very hot. I change it and the same was happening. Then I change the IT8528E IO Chip but again the same happens.

I then found out that 3 coils and a lot of capacitors are shorted to ground. Also all the capacitors on the CPU BGA are shorted.

Is there any way to find out where the short starts?
I don't have the schematic to see how the circuit goes.
The motherboard doesn't write any model except from Chip Main Board V2.1

[khaahk]

Re: IdeaPad s500 Touch sorted

Find a datasheet for TPS51225, there are LDO outputs and SMPS outputs. Measure resistance of both - which one is shorted?
Use a lab power supply to find short on the rail. The method is described in this forum or google for it.
CPU itself is low resistance - so 3-5 ohms is not a short.

[John_F_L]

Re: IdeaPad s500 Touch sorted

None of the outputs of the TPS51225 are shorted.
I forgot to mention that 3,3V and 5V are present on the system.

[khaahk]

Re: IdeaPad s500 Touch sorted

So vreg3 and vreg5 are 3.3 and 5V respectively?
SW1 and SW2 are also outputting?
Just the tps is getting hot?
What resistance do they have?
How much current does the mainboard use when plugged in?

What resistance do you have on the cpu caps?

[John_F_L]

Re: IdeaPad s500 Touch shorted

SW1 = 3.6 Kohm 5mV
SW2 = 4.1 Kohm 20mV
VREG 3 = 0.745 ohm 3.3V
VREG 5 = 3.4 Kohm 5V
The lab power supply won't go over 0,05A.

Almost the same measurements and with a new TPS

Caps on CPU max resistance was 2.7 ohm

edit:
After installing again the TPS (to be sure that it was OK on the board) I have 3.3V on SW1 and 5V on SW2. And also the resistance of the VREG5 went on 12 Kohm. All the others are the same.

[khaahk]

Re: IdeaPad s500 Touch sorted

VREG 3 resistance is too low. That is why the chip is overheating.
Inject voltage from lab supply and see who else is heating up. (LAN maybe or something else)

[John_F_L]

Re: IdeaPad s500 Touch sorted

I don't see anything else heating up.
But my problem still is not why the TPS is heating but why so many components of the machine are shorted to ground. If the TPS is out of the circuit, it is still shorting so that is not my cause.

[khaahk]

Re: IdeaPad s500 Touch sorted

0.7 ohms on VREG3 rail is a problem.
low resistance (which might not be a short) on random places on board - hard to comment without schematic available.

[John_F_L]

Re: IdeaPad s500 Touch sorted

Propably the rail as you told.
I tried also to remove some big components like inductors, the big caps, and some mosfets but nothing changed.
The last thing I tried was with freeze spray the first time and alcohol the second to see where it might get hot, but the only thing that was heating up fast was the TPS.

[khaahk]

Re: IdeaPad s500 Touch sorted

If i had the mainboard at hand i would:
remove tps
solder a lead to VREG3
Put 3.3V to it from LAB supply (1A at first, if needed up to 3A or more)
something must become hot, if big chip (like PCH) then might only be slightly warm

[John_F_L]

Re: IdeaPad s500 Touch sorted

I tried what you said but the Amper won't go over 0,03A on my Power Supply, no matter how much I turn the dial.
I tested that the lead won't touch anything else nearby.
So definetely something wrong with the rail.