Lenovo IdeaPad FLEX 5-1570 81CA totally dead

[mferna14]

Hi, Does anyone have the boardview for Lenovo IdeaPad FLEX 5-1570 81CA LA-E541P. Schematics is posted but I need little help finding the components. The motherboard in this is CIUYA/SA/SB/SD LA-E541P. Another know how.. I remove PQ712, I get all the voltage on the Gate of PQ740 which is 24.5V a true voltage out here meaning ISL88739HRZ is working fine, but as soon I solder PQ712 the voltages drop again. PQ712 is not short & I also checked PQ707 (Protection) all seem to be fine. Do you think I should replace PQ712??? I also check PQ705 & PQ305 (Battery Charging MOSFETs) & the surrounding caps., all seem to be fine. I removed the resistor PR913 to check if any short further but still the same. So there is something going on before this resistor. How come voltage is dropping??? Any help will be greatly appreciated. Thanks

[Sephir0th]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

This is at least a wild Story and you missed the Organized way to troubleshoot the Board properly. And You didn't shared any measurement. You desoldered the Current Sense Resistor for No reason. I never Heard of one failing, and so on...

Now you have to be more concentrated. Let us start with the following.

At First, solder the PR913 Back in place. Then, what is the Résistance to GND of PR913 (any Side)?

[mferna14]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

I soldered back the resistor & it 1 ohms (010). Removal of the resistor does not make the difference. Once I remove the PQ712, I get gate voltage on PQ740 24.5V which is a true voltage., & this Gate voltage is directly connected to the gate of PQ712 & this is turn on to pass the 19v on the drain & then comes the 1 ohm resistor. So whatever is happening is all behind this MOSFET & resistor.

[Sephir0th]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

I know the value of the Current Sense resistor and this was not the Question. Remove all power, Grab the Multimeter, Set it to Ohms Mode, Range 200, Red Probe at the Resistor and Black Probe to GND and Share the value here.

Most likely your Main Power Rail is Short to GND. This is the reason why the Voltage can Not Pass the Second DC-IN Mosfets.

This is a simple and usual fault on Motherboards. But If you still persist on Not doing Basic troubleshooting and Not Sharing any value, Nobody can Help you.

If the Problem is elsewhere, then explain it properly. You're Not new Here so i really don't Understand what you're doing Here.

[mferna14]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

See I knew the problem was before this PQ740... MOSFET PQ707 was shorted, replaced it, all works fine. Just used Technical knowledge & brains & trouble shooted step by step. Motherboard work 100% fine. Thanks for all the help "Sephir0th"., it was great you guiding me.

[mcplslg123]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

@mferna, you may have solved this problem but definitely your troubleshooting was not upto the mark. @sephiroth guided you correctly but you ignored that. If you would have removed CLR and measured resistance on both sides, you would have been sure that short is on which side and i think that's the correct way.

[mferna14]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

I do understand, but it did not seem logical to me.. I Read & studied the schematic very well. It isn't logical to remove the current resistor when the short was before this. There was no short on the resistor point even after removal. Pls. view the Schematic & study well. It's very nice to argue as we all learn a lot from all of this, thank guys for all the help & hope we have learnt from this trouble shooting.

[Sephir0th]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

Likely PQ707 was shorted beetween Drain and Gate. Then this all makes Sense.

AND... If you Would have shared from the beginning where the short to GND is located it Would have been a fast repair.

[mferna14]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

"Sephir0th" , yes you are right (Drain & Gate), when the power adapter was connected then the ISL chip as once detected this short & put it into protection mode though the protection circuit was short & never let the true 19v pass through the PQ712. This is why I kept on repeating that the voltage has not even reached the resistor so there was no sense of its removal as I had already removed PQ712. Thank you guys for all your help, really learnt a lot from this repairs.

[ajbernasko]

Re: Lenovo IdeaPad FLEX 5-1570 81CA totally dead

please can you provide the ISL chip information/part number ?