ACER ASPIRE 5942G-724G50Mn -Problem: it turns on and off continuously by itself

I was looking to my webmail when suddenly the display goes black...
From that moment if I turn on the pc, it turns off by itself after a few seconds and turns back on by itself in an infinite loop. Display always black.
Before switching off, the Fn F9 sequence switches the keyboard backlight on and off correctly.
You hear that it accesses the DVD and the hard drive but then turns off and then on again.
I removed the hard drive and the dvd drive but the problem remains.
Only if I remove both RAMs the PC remains on.
If I just put a RAM bank, the problem arises.
I opened the PC and disconnected the RTC battery for two hours. The battery is ok and measures 3.1 volts. I re-soldered the battery but the problem remains.

What can it be? motherboard failed?

Can I try to disconnect the monitor, turn on the PC and see what happens?
Why Fn-F9 works properly?

Thanks in advance from Italy

Accepted answers

All comments

JackE

Still Windows 7? Jack E/NJ

Paolo6

Yes, all original.

The sequence seems extremely regular: I press the power button, the fan turns on immediately and after 1 second you hear the usual short noise from the CD / DVD drive (empty), another 5 seconds (you hear that the hard drive starts spinning ) and labtop turns off: after 1 second it lights up again by itself, and then again in a continuous cycle. The monitor always remains off.

If I remove hard disk, nothing changes.

I suppose that if it was a graphic card failure, when if turns off it should remain off... why it switches on again?

Maybe BIOS corrupted?

Hardware or firmware failure?

Thanks

JackE

>>>Maybe BIOS corrupted?>>>

How do you think that could've happened? Jack E/NJ

Paolo6

It was only a question. There is no reason for the bios to be corrupted.
What can I do?

JackE

>>>Only if I remove both RAMs the PC remains on>>>>>>The [RTC] battery is ok and measures 3.1 volts.>>>

Do you hear a BIOS beep code when you turn it on with the RAM modules removed? Jack E/NJ

Paolo6

No. Simply I dont hear access to the hard drive

Paolo6

I also tried to mount another RAM, but nothing changes

JackE

>>>The [RTC] battery is ok and measures 3.1 volts.>>>

Measure voltage when it's still connected to the mainboard. Jack E/NJ

Paolo6

Voltage remains 3.1V

JackE

What happens when you press the FN+F6 or FN+F5 screen toggle key combination during the loops? Jack E/NJ

Paolo6

Something happens....sometimes....
While I toggle Fn F5, once every 10 /20 Times the PC remains ON. Loop stopped.

Only once while toggling fnf5 fnf6 the backlit of the display powered on (with no characters) before switching off

JackE

I now suspect the LCD video ribbon cable may have a broken or shorted conductor traces. Please disconnect the ribbon cable at the mainboard. Then if possible connect an external TV or monitor via the HDMI or VGA port. Try to turn it back on. Do you see an external TV screen? Jack E/NJ

StevenGen

Have you tried using another HDD? With the Ram and DVD/CD installed? Go through a process of elimination of all these components. As it could be either your HDD/Power source/Ram/Display (as JackE suggests) or DVD/CD that are the culprits but, it sounds like its your LCD or HDD, so use another HDD and/or another external display, see if helps at all. Let me know what happens'

Paolo6

I opened the PC and disconnected two connectors: LVDS (flat) and the conductive cable (6 pin). I reconnected all the peripherals except the bluetooth module.

I connected a TV via HDMI and then turnedthe PC on.

On the TV monitor, without pressing any key, a Windows error screen appears asking me to reset the Windows configuration due to hardware changes.

The image on the TV screen is very noisy with rbig vertical lines disappearing if I press any key to continue- The image remains very noisy-

Keep in mind that the PC is not closed so it may not be adequately shielded

It says (in italian):

Restore from windows errors

Windows startup failed. The problem may be due to recent changes to the hardware or software.

Launch windows recovery tool.

Should I Disconnect Only the LVDS Cable?
How to proceed to detect if one of the cables or LCD is faulty?

Many thanks

Paolo6

I referred to this Service guide:

www . informaticanapoli . it / download MANUALI / Acer / aspire%205942%205942g . pdf

picture 13 on page 80 (pdf #92) and picture 14 on page 81 (pdf #93)

JackE

Yes, disconnect the LCD video cable at the motherboard to see if the TV screen gets better. You don't have the equipment to test the video cable or LCD screen itself. A new video cable is cheap. A new LCD is expensive. So you buy a new video cable to test if it's the cable or the LCD. Jack E/NJ

Paolo6

Unfortunately it seems that you can't change only the cable but all the LCD module...
I have left disconnected only the big connector of the display and closed all.
Connecting a TV monitor the screen is always very noisy: is it normal or something is wrong?

JackE

No!!!! The video ribbon cable is separate from the LCD module and can be replaced separately. https://www.aliexpress.com/i/4000167836188.html

It must be disconnected from the mainboard connector, NOT from the LCD connector (which is known as an inverter board). This must be done so the video ribbon cable is isolated from and does NOT interfere with the signal to the TV screen.

Jack E/NJ

Paolo6

Do you mean that -from the motherboard- I must disconnect both connectors and not only the big one (LVDS) otherwise the cable may interfere with the TV screen?

JackE

There's only one connector on the motherboard/mainboard. The other two connectors go to the lid videocamera and the lcd screen board. Only disconnect the circled mainboard connector shown below. Jack E/NJ

Image: https://us.v-cdn.net/6029997/uploads/editor/6u/bb0knfo241az.jpg

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