Acer 5750G P5WE0 LA-6901P images only on external screen

[Paul20]

Hi everybody,
I have a problem with this Aspire 5750G P5WE0 LA-6901P Rev. 2.0.
Everything works normally, but displays only on the external monitor and not on the integrated one.
I found a short in the Lcd Power area, exactly on the Motherboard pitches of Q1 2 and 3 in short (with component detached).
No voltage arrives on the LVDS connector on pins +LCDVDD 24 and 25.
I think the enable of PCH_ENVDD is missing, but I can be wrong.
I have an identical card in perfect working order, so I was able to do all the measurements, but I couldn't solve anyway.
Is there any way around this problem?
Can anyone give me some advice?
I'm afraid the problem is serious, but I await someone more experienced.
Thanks to anyone who wants to participate.

[Paul20]

Re: Acer images only on external screen

I was thinking something.
At the moment R3 is missing and from the scheme this would lead ENVDD to Q1.
What if I move R1 to station R3? Could this work or am I in trouble?
I noticed that by removing R1 the short on the pins of Q1 disappears.

[caspian]

Re: Acer images only on external screen

first remove R1 and measure resistance on each pad of it.
Moving R1 to R3 probably has no danger and probably does not solve the problem.
Does this laptop have a dedicated GPU chip?

[mon2]

Re: Acer images only on external screen

Try this (only for testing) - remove R1 and be sure R3 is not present on the board.

Then with a wire, connect pin #2 of Q1 (2N7002 mosfet) and connect it to the +3VALW rail.

This will then turn Q1 ON and emulate the signal that appears to be missing from the PCH_ENVDD signal line.

BTW - if R1 is stuffed, then you have UMA mode on the logic board. Is this how the logic board was assembled ?

On this topic, you can confirm the UMA strapping here:

https://www.youtube.com/watch?v=IUH2hB30YWs

[Paul20]

Re: Acer images only on external screen

first remove R1 and measure resistance on each pad of it.
Moving R1 to R3 probably has no danger and probably does not solve the problem.
Does this laptop have a dedicated GPU chip?

I measured the resistance on the pads of R1 and found: on pad 1 0.606 and on pad 2 0.124
It has separate GPU.

[Paul20]

Re: Acer images only on external screen

Try this (only for testing) - remove R1 and be sure R3 is not present on the board.

Then with a wire, connect pin #2 of Q1 (2N7002 mosfet) and connect it to the +3VALW rail.

This will then turn Q1 ON and emulate the signal that appears to be missing from the PCH_ENVDD signal line.

BTW - if R1 is stuffed, then you have UMA mode on the logic board. Is this how the logic board was assembled ?

On this topic, you can confirm the UMA strapping here:

https://www.youtube.com/watch?v=IUH2hB30YWs

I have unplugged R1 and there is no R3, so I have jumpered pin 2 of Q1 with + 3VALW, but still short on pins 2 and 3 of Q1.
So as in the beginning when R1 was connected.

[caspian]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Are the resistance relative to GND?
It is strange that both the pads are shorted.

[mon2]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Remove this gate wire used for testing. Do not stuff R1.

Reflow Q1 with flux and low air pressure.

No power to the logic board.

Check resistance to ground on pin #2 of this mosfet.

What is the resistance?

Consider to replace Q1, it is a very common part. This is the 2N7002 device.

Of concern is why the gate is not being driven through R1 and the upstream PCH signal.

The short between pin #2 and #3 of Q1 should not be there. I recall a pull down resistor on the gate - remove it. Presently do not have the schematic loaded but check this resistor as well to fix this shorting issue.

You can also check the diode mode reading of the pch output pin. No power. Meter in diode mode. Red meter lead to ground. Black to the floating R1 pin that is to the PCH side.

Diode mode reading?

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Are the resistance relative to GND?
It is strange that both the pads are shorted.

Resistance to ground, yes.
Exactly, the problem is this.

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Remove this gate wire used for testing. Do not stuff R1.

Reflow Q1 with flux and low air pressure.

No power to the logic board.

Check resistance to ground on pin #2 of this mosfet.

What is the resistance?

Consider to replace Q1, it is a very common part. This is the 2N7002 device.

Of concern is why the gate is not being driven through R1 and the upstream PCH signal.

The short between pin #2 and #3 of Q1 should not be there. I recall a pull down resistor on the gate - remove it. Presently do not have the schematic loaded but check this resistor as well to fix this shorting issue.

You can also check the diode mode reading of the pch output pin. No power. Meter in diode mode. Red meter lead to ground. Black to the floating R1 pin that is to the PCH side.

Diode mode reading?

I did the tests you suggested.
With R1 detached (if I understand correctly) on pin # 2 of Q1 resistance to ground OL.
Then test in diode mode on pad # 1 of R1 (always detached) 1108.
The output pin of PCH_ENVDD is on R1.
In fact I imagined it was serious, just because Q1 is not driven and does not activate LCDVDD_ON which would turn on the display, if I'm not mistaken.
Even if you want to replace Q1, the short remains anyway, the main problem is that.

[mon2]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Remove Q1. Do you still have a short on the pads where Q1 was soldered?

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Remove Q1. Do you still have a short on the pads where Q1 was soldered?

It is always short.
The short comes from pin # 1 of R1, which would be PCH_ENVDD, with or without Q1 the short is always present.

But that ENVDD which is on pad # 1 of R3 (R3 is absent), cannot activate Q1 equally?
Because at this moment it is as if it were deactivated, given the absence of R3.
On pad # 1 of R3 comes ENVDD, if you close this point, on the boardview, it tells me that it would activate LCDVDD_ON, just like it does with R1.
If I close this point, could it not activate Q1?
But maybe I'm saying nonsense, I attach pictures.

[mon2]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Without R1 & no power to the logic board.

Meter in lowest resistance scale.

What is the exact resistance in ohms to ground on PCH_ENVDD ? (R1, pin # 1 pad)

Also post the resistance scale used on the meter.

If the resistance is truly low, then diode mode should beep. Can you confirm it? Switch to diode mode, red meter lead to GROUND. Black meter lead to PCH_ENVDD (R1, pin # 1 pad). Does the meter beep / send out a tone ?

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Without R1 & no power to the logic board.

Meter in lowest resistance scale.

What is the exact resistance in ohms to ground on PCH_ENVDD ? (R1, pin # 1 pad)

Also post the resistance scale used on the meter.

If the resistance is truly low, then diode mode should beep. Can you confirm it? Switch to diode mode, red meter lead to GROUND. Black meter lead to PCH_ENVDD (R1, pin # 1 pad). Does the meter beep / send out a tone ?

I state that I do not have professional measuring instruments, only hobby, unfortunately.
With digital meter set to 200 Ohm which is the minimum for this meter The maximum is 2 M Ohms, it gives me no reading.
In diode mode, red to ground and black to PCH Pad # 1, steady beep.

Using another measuring tool (SMD TESTER) in automatic Ohm mode, it marks me 2.9 M Ohm.
Beep mode, OL.

[mon2]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

I do not think that you have a short on this line.

With digital meter set to 200 Ohm

Use this lowest setting and then short the meter probes together - what is the reading on the meter ?

Then apply one probe again on the PCH_ENVDD pad (R1, pin #1 pad) and the other meter probe to ground.

What is the resistance reading ? If you see '1' or 'OL' - this means the meter is stating the resistance is higher than the scale that was selected on the meter. This is a good sign.

Confirm the above.

However, the PCH_ENVDD output should be a valid higher voltage (~3 volts is ok) to enable Q1 mosfet. We attempted to do this with the jumper wire.

Do you have spare Q1 mosfets you can solder in ? Still keep R1 off and we can try with the manual jumper wire from the gate of Q1 mosfet to ~3 volts.

This should turn ON the Q1 mosfet.

[mcplslg123]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Q28 checked?? Remove C2/C10/C479/C483 and check if the short is still there or not??

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

I do not think that you have a short on this line.


Use this lowest setting and then short the meter probes together - what is the reading on the meter ?

Then apply one probe again on the PCH_ENVDD pad (R1, pin #1 pad) and the other meter probe to ground.

What is the resistance reading ? If you see '1' or 'OL' - this means the meter is stating the resistance is higher than the scale that was selected on the meter. This is a good sign.

Confirm the above.

However, the PCH_ENVDD output should be a valid higher voltage (~3 volts is ok) to enable Q1 mosfet. We attempted to do this with the jumper wire.

Do you have spare Q1 mosfets you can solder in ? Still keep R1 off and we can try with the manual jumper wire from the gate of Q1 mosfet to ~3 volts.

This should turn ON the Q1 mosfet.

With the meter set to 200 Ohm, short with the probes mi from 005.
Applying one probe to ground and one on Pad 1 of R1 PCH_ENVDD gives me 1, so you say this is good.

I found another 7002 from a recovery card and soldered it.
Is the next step as before? Jumper pin 2 of Q1 to + 3VALW on R6?

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Q28 checked?? Remove C2/C10/C479/C483 and check if the short is still there or not??

I confirm that I have already tried to unplug all the components you have listed for me, before starting this post, but the short on pins 2 and 3 was always there.

[mon2]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

PCH_ENVDD gives me 1, so you say this is good.

Yes, this is good. It is the low cost method for the meter manufacturer to let you know that the meter scale is too low for the resistance being measured.

Switch to a higher scale till you get a true reading. Either way, this signal line is NOT shorted to ground.

Confirm this first.

Next, confirm the voltage for +3v is available so we can borrow it for testing.

[Paul20]

Re: Acer 5750G P5WE0 LA-6901P images only on external screen

Yes, this is good. It is the low cost method for the meter manufacturer to let you know that the meter scale is too low for the resistance being measured.

Switch to a higher scale till you get a true reading. Either way, this signal line is NOT shorted to ground.

Confirm this first.

Next, confirm the voltage for +3v is available so we can borrow it for testing.

Before having a measurement I have to pass on the maximum scale of 2 M Ohms and therefore it gives me 1,600 and a little more.

Then if I try to jumper pin 2 of Q1 to + 3VALW on pin 1 of R6, there is a short with the meter in acoustic mode always on both pins 2 and 3 of Q1.
All this always with the R1 detached.
Maybe I'm wrong to explain, but I don't think so.

However I confirm that the + 3VALW are present on R6.