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

[mon2]

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

Wish to confirm / note that you cannot perform resistance or diode checks if there is power to the logic board. It will not work.

You must have all power removed for these tests unless we are discussing voltage checks.

[Paul20]

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

Wish to confirm / note that you cannot perform resistance or diode checks if there is power to the logic board. It will not work.

You must have all power removed for these tests unless we are discussing voltage checks.

Yes this is clear, and I already knew it, in fact I performed all the tests without power supply, God forbid.
So do you think it is possible to do a test by jumpering the + 3VALW on pin 2 of Q1?
Or do other tests need to be done?

[mon2]

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

What are the voltages on pins 1-2-3, 5 & 6 of the LCD connector (with the LCD connected) ?

These are:

1-2-3 : +INVPWR_B+
5 : DISPOFF#
6 : INVTPWM

Review the voltages on mosfet @ Q28.

Is pin # 3 = ~3 volts ?

If yes, voltage on pin # 2 = gate ?

Pin # 1 = is the pin that powers the LCD and it should be ~0 volts by default.

To turn ON Q28 to pass the voltage through, the GATE voltage should be 'negative' or lower than the source voltage.

That is, if you GROUND the gate of Q28, this mosfet should turn ON.

Take a jumper wire and connect to pin # 2 (gate) of Q28 & other side of the wire to GROUND.

Does this allow for the +LCDVDD pin to receive ~3 volts (through Q28, pin #1) ? Do not worry about Q1 as the effect is the same. If Q1 closes, then Q28 gate pin will be shorted to ground to turn on Q28.

Q28 = P-channel mosfet so needs a LOWER voltage on the gate than the source pin (which should be ~3 volts on your box) to turn ON.

Q1 = N-channel mosfet so it needs a HIGHER voltage on the gate than the source pin (which is 0 volts) so ~3 volts will fully turn on Q1 mosfet.

Mosfets = like a water tap (have thoughts of drowning this circuit right about now).

[Paul20]

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

All clear, therefore:

Voltages with the LCD connected on pins 1-2-3 are 18.9V.

On pins 5 and 6 no voltage.

A note, my boardview, gives me pins 5 and 6 not connected, while pin 6 BKOFF and pin7 INVTPWM, I checked these too for safety and there is no voltage.

The voltages on the Q28 are about 3.3V on pins 2 and 3 ... on pin 1 0V.

I also checked Q1 and on its pin 1 there is about 3.3V

So you think everything is ok?
Do I proceed with the connect you told me about the Q28?
The mass can I take it from C2 immediately close to Q28?

[mon2]

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

Yes, looks logical on the readings.

To force Q28 mosfet (P-channel) to turn ON, yes, you can apply a jumper wire on C2 (pin # 1) and can short it to:

a) C2, pin # 2 (since this is GROUND)

(could even use tweezers but a wire is more stable to handle)

or

b) Ground anywhere else that is convenient.

Then Q28 should turn ON and pass the voltage onto Q28, pin # 1. This voltage should then reach pins 24 & 25 of the LVDS display connector.

Check it.

[Paul20]

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

Here are the updates.

I connected pin #2 of Q28 to ground taken from pin #2 of C2.

When the card is turned on, on pin #1 of Q28 I find 3.3V and consequently also on pins 24 and 25 of the LCD connector.

The screen seems to want to start, but it stays black, not off, but it appears to be on but completely black.

Against the light you can't see anything.

The screen works perfectly, tested with a fully functional Motherboard.

Something still seems to be missing.

[mon2]

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

You may be missing some other required signals to drive this display.

Attach the same display to your other but working box.

Measure the voltages on each LVDS connector pin.

Then do the same for the non-working board.

Post the readings so we can compare.

[Paul20]

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

Not working motherboard:

Pin 1, 2, 3 - 18.9
Pin 4 e 5 - NC
Pin 6 e 7 - 0
Pin 8 - NC
Pin 9 - 006
Pin 10 - 006
Pin 11 - GND
Pin 12 - 006
Pin 13 - 006
Pin 14 - GND
Pin 15 - 012
Pin 16 - 012
Pin 17 - GND
Pin 18 - 2,34
Pin 19 - 2,34
Pin 20 - GND
Pin 21 - 003
Pin 22 - 014
Pin 23 - 3,3
Pin 24 - 3,3
Pin 25 - 3,3
Pin 26 - 0
Pin 27 - 3,3
Pin 28 - 002
Pin 29 - 002
Pin 30 - GND


Working motherboard:


Pin 1, 2, 3 - 18.9
Pin 4 e 5 - NC
Pin 6 e 7 - 3,3
Pin 8 - NC
Pin 9 - 1,23
Pin 10 - 1,19
Pin 11 - GND
Pin 12 - 1,19
Pin 13 - 1,25
Pin 14 - GND
Pin 15 - 1,05
Pin 16 - 1,36
Pin 17 - GND
Pin 18 - 1,06
Pin 19 - 1,37
Pin 20 - GND
Pin 21 - 3,3
Pin 22 - 3,3
Pin 23 - 3,3
Pin 24 - 3,3
Pin 25 - 3,3
Pin 26 - 0
Pin 27 - 3,3
Pin 28 - 002
Pin 29 - 002
Pin 30 - GND

[mon2]

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

Pins 6 & 7 are LOW (0 volts) on the non-working board which means the logic board is requesting that the display remain OFF.

DISPOFF# has the '#' symbol which denotes an ACTIVE LOW signal. So if this line is LOW, the display will be OFF.

DISPOFF# is tied to BACKOFF# which is linked through R13 to the KB930QF (pin #104).

Confirm that R13 is present on the logic board.

Next step I think should be to reflash the KB930QF device. No experience in this area so wait on others to comment. Perhaps this controller has corrupted firmware.

I am assuming that your lid sensor is working since you can work with an external screen.

[Paul20]

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

R13 I can't find neither on the diagram nor on the boardview in my possession, so I can't search on the motherboard, maybe we look at slightly different schemes.

BKOFF in my case is connected to R375 (not present on Motherboard) Pin 2 BKOFF pin 1 + 3VS.

BKOFF connected to KB930QF is on pin 105

If KB930QF needed reflash, I wouldn't be able to run it, as I don't have a programmer.

[mon2]

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

I have a very bad schematic for this logic board. My schematic lines are not aligned with the component symbol. More crapware.

Is your version of the schematic any better ?

Can you link or post it here if on the forum ? Want to be 110% sure we are referencing the same logic board.

[Paul20]

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

I have a very bad schematic for this logic board. My schematic lines are not aligned with the component symbol. More crapware.

Is your version of the schematic any better ?

Can you link or post it here if on the forum ? Want to be 110% sure we are referencing the same logic board.

My Motherboard is exactly that of the scheme I am using, same for the boardview.
If I can post it here on the forum, I do.
I simply downloaded it from the internet, but I don't want to risk infringing any copyright.