Lenovo Z50-70 on but no post, black screen

[erbuzzicker]

Hello guys,

I have a Lenovo Z50-70 laptop (schematic in attachment) with motherboard ACLUA/ACLUB NM-A273 with no post issue: after pressing power button, power led comes on but laptop doesn't switch on, no screen.

Following the sequence shown at page 47, I don't have PM_SLP_S3#
PM_SLP_S4#. The abnormal thing is also that when i press power button, PBTN_OUT# correctly dropps from 3.3v to 0v but after releasing it, it stays at 0.


I can't understand if it's a SIO issue (I have already tried to flash main end EC bios) or PCH issue.

Can you please help me to understand?

Thanks

[erbuzzicker]

Re: Lenovo Z50-70 on but no post, black screen

I would like to add this additional info and abnormal thing that maybe can help you to better understand the issue

[mcplslg123]

Re: Lenovo Z50-70 on but no post, black screen

Q26 is not populated from factory(there is @ mark which means the component is not used). Q25 is n channel-so its gate(susp) must be low to block ground(S) travelling to Drain)D) pin. Then only +20VSB will pass through resistor R149 and reach the gate(pin4) of Q23 which in turn will allow +5VALW to pass as +5VS on pin 1-2-3. Unless these conditions are fulfullied, you wont get anything on +5VS pins.

Check resistance on pin 1-2-3 of Q23. Check the mosfet as well for short. Do the same for +3VS mosfet.

[erbuzzicker]

Re: Lenovo Z50-70 on but no post, black screen

Ok, it's clear that because of Q25 gate is always 5v, I cannot have +20VSB going to Q23 gate and enabling +5VALW to become +5VS. The same issue I have on the +3VALW section (image in attachment), where Q27 gate is always 5V and make this section shorting to 0.

So my question is: don't you think it is not a problem of Q23 (and Q24) mosfet but of SUSP signal going on Q25 and Q27 gates that should become 0v?

Thanks for your help and interest in this case

[mcplslg123]

Re: Lenovo Z50-70 on but no post, black screen

Yes, i too doubt that problem is SUSP signal not going low when turned on but repair is not carried on doubts alone. So you have to try by removing Q25 to see if +VSB passes on.

[DanielDacko]

Re: Lenovo Z50-70 on but no post, black screen

Change r149. It's obvious that it is the culprit.

[erbuzzicker]

Re: Lenovo Z50-70 on but no post, black screen

Change r149. It's obvious that it is the culprit.

I don't think it's so obvious as I don't think it's the root of the issue. Even if R149 is good, if Q25 is faulty this can cause the line to be shorted to ground so R149 will be 20V on pin 1 and 0v on pin 2.

I will try to remove Q25 to see if +VSB passes on as suggested by mcplslg123 and let you know if the problem is still there.

[erbuzzicker]

Re: Lenovo Z50-70 on but no post, black screen

Yes, i too doubt that problem is SUSP signal not going low when turned on but repair is not carried on doubts alone. So you have to try by removing Q25 to see if +VSB passes on.

I have tried to remove Q25 right now to see if +VSB passes on through R149 resistor and it does. So Q23 mosfet has ben activated to let 5VS as well as Q24 mosfet to pass 3VS: anyway laptop continue to not posting even if removing Q25.

To see if Q25 is bad, I have replaced it with a good one but same issue, so I think that this confirm that the problem is the SUSP line...

Any idea?

[erbuzzicker]

Re: Lenovo Z50-70 on but no post, black screen

Any help please?

[mon2]

Re: Lenovo Z50-70 on but no post, black screen

SUSP is created on sheet 46/59 from SUSP#.

What is the voltage of SUSP# = pin 2 of Q6A ?

[erbuzzicker]

Re: Lenovo Z50-70 on but no post, black screen

SUSP is created on sheet 46/59 from SUSP#.

What is the voltage of SUSP# = pin 2 of Q6A ?

Pin 2 is 0 V so pin 6 is 4.9 V

[mon2]

Re: Lenovo Z50-70 on but no post, black screen

1) Connect pin 6 of Q6A to ground => SUSP = LOW.

SUSP is in an open-drain configuration so there is no harm to connect pin 6 of Q6A to a ground connection.

2) What is the voltage on Q24 - pins 1,2,3 after this strapping ? This is +3VS it powers the IT8586E via VCC pin # 11.

[ktmmotocross]

Re: Lenovo Z50-70 on but no post, black screen

have one just same symptoms

NO SUSP
no reaction to PWB, except one led. No voltages been released

flashed bios+ec, replaced ec