Hi,
I have got Acer V3-571 laptop with following symptoms.
01. When I turned it on power LED lights up for 5 senconds and turned off.
02. +3.3v and +5v available and +3VL and VLP (VREG3 andVREG5) are also available.
03. When I turned on the laptop U21 and U22 FETs does not turned on and not produced +3VS and +5VS
04. "SUSP" signal not coming to the Q19 and Q25 which are triggering the gates of U21 and U22.
05. Then I checked Q27 for "SUSP" signal. Unfortunately "SUSP#" must be there to generate "SUSP" signal.
06. "SUSP#" generates from KBC (ENE KB9012).

Therefore where to start to solve this problem.

Voltage KBC (ENE KB9012) and chip bios correct? Firmware right? If so then KBC (ENE KB9012) died

kandyan
Check
LID_SW# - must be high
ON/OFF - triggered by power switch
PBTN_OUT# - triggered by power switch
PCH_RSMRST# - must be high

KB9012 has internal firmware (EC firmware). Try to reflash it (you need the special programmer to do this).

It might be and i changed it also.nothing good




I changed KB9012 and reprogrammed it with "Maxim" s KB9012 programmer.
http://notebook1.ru/forma1/viewtopic.php?p=534436

Now all other signals are ok but PCH_RSMRST# doesn't show anything high. I suspect South bridge is the problem is this case according to the symptoms. Shall I reball it or is there anything to check before reballing it?

Check what PCH_RSMRST# has no short cut.
Check +RTCVCC
Check XTAL25 on Y2 generation present

I didn't find anything abnormal in PCH_RSMRST# and
+RTCVCC is present +3V
XTAL25 on Y2 is working when RTC battery is on the battery bay. (Checked it with oscilloscope)

Now I really think that problem is on south bridge bcz in this model there is no heat sink for it. So there is a dry contact under the PCH. I will reball it and let you know the results.

Do you reflash main BIOS?

Yes I did. Main,Win8 and EC.

Everything works well after i reballed the South bridge. Thanks everyone for the help.
and also when Dell 3521 boot up without display and making beeps sounds its better to reball the south bridge as well.
Bcz I have reballed 1 beep, 4 beeps and 8 beeps dell inspiron 3521 and problem was solved.