Dell 3521 LA9104p.No power

[ganeshcell]

19v is ok but 3.3v and 5v is not present.there is no shorting in 3.3v and 5v.i have replaced pu200 but same problem.plz help

[chandra]

u replace 3v and 5v

[ Post made via Android ]

[ganeshcell]

yes i have replaced 3v 5v regulater EM=FF.but same problem

[Elcobra]

Hi, 3521 has enormous problems with bios chips, first of all it has to beep, when u turn it on does one beep? if it does its from bios and more specific is the w25q32 which is located underneath kbc, reflash it and it will work, in case u dont have the bin tell me and i will put it here, case 2: in case the laptop doesnt turns on at all no lights no beeps no nothing than u have to reflash the firmware of kbc which is located near kbc, w25q16, in case u dont have the bin tell me i will upload it.
this is the case when u have the main power supply 19v and 3,3 and 5v, 90% of cases what i told u to do will solv it.

[ganeshcell]

this is not the firmware problem.3.3v and 5v is not generating.

[Elcobra]

Than its easy fix:D first of all check if u have 19v on pin16 of the circuit tps51125, if u have than check without power plugged in the impendance to ground from the 5v coil output and 3v3, so u can check if u have a short on 5v or 3v3 rail, if its ok than check on tps51125 what voltage u have on pins 1 and 6 if u got 0 the chip is shutdown down u need to have around 1v there and clasic schematics uses a 130K resistor to ground and in another schematics those 2 pins are used with a double transistor to shutdown the rails or to switch it on, and the most important u need to measure the 3.3 ldo on pin 8 which powers the spi firmware and some blocks from keyboard controler, if u dont have the 3.3v measure against the ground and see what impedance u have, if is low like <50 ohms most probably or kbc is fried but in this case the tps51125 should get warm, if its the case unsolder the kb9012 and measure again and u should have high impedance, change the kbc and it will work

[Elcobra]

Now i read that u have no shorts on rails, i dont have the schematics on 3521 but check the voltages on pins 1 and 6 and very important check if it leads to a duble transistor is in package of 6 pins:D, if it does remove it and the rails should be turned on, if thats the case it means that 1) u have no 3.3v LDO on pin 8 and and kb9012 aint powered and neither the 25q16 and the gpio that commands that transistors is low, in case that there is 3.3 on the LDO and u removed the transistor and rails turns on than it means that ec firmware from kbc its corupted, btw i found a 3521 board and i can give u more details:D it is with transistors and it near chip tps51125 and its marked pq206 its a double transistor and when laptop its off the base of transistor is pulled high to 0.7v and emiter colector are shorted and puts the pins 1 and 6 to ground, when laptop is powered on the the base is low and there is high resistance across emiter colector which activates the chips rails.

[Rabin17]

If there is no 3.3 & 5v then check pin no 23 ( pgood signal) 4.5 volt of tps51125 or rt8027 or j7.
if this signal is missing then resolder this chip or replace the chip. before doing that must have to check there is no short in m/b. if there is no short then do this. problem will solve. thanks.

[Elcobra]

( pgood signal) appears only when both supplyes are running, read what pgood does and how it works cause u got it all wrong my friend, if he cheks what i told he has repaired it by now

[anil999]

psu amp ? 0.004?