Aspire 7750-6423 backlight is out. Tried keyboard tricks and BIOS load---negative result.

Piper35
Piper35 Member Posts: 5 New User

Replaced LCD screen and still no backlight. Troubleshooting charts say replace MB. MB is P7YEO_U98 .  Is there different number for the MB?  Any other backlight solutions to try?

PS: It is working with an outboard monitor using the 'D' connecter.  While I was using that method to update Windows the backlight popped on and stayed for the session.  Have not gotten it back after multiple tries.

Answers

  • Did you also replace the inverter? If not, that could be the problem.
    However, as the problem is intermittent, it is most likely a poor connection or broken cable. If a visual check doesn't reveal the fault, you could try a continuity test. Another test is to partially open and close the lid to check for on/off or flicker which would also indicate poor connection, broken cable or fractured ribbon cable.
    Personally, I wouldn't suspect the motherboard until all the above have been thoroughly checked and proved to be good.
     

  • philetus
    philetus ACE Posts: 4,759 Pathfinder

    I would look at the connection where the DC-IN cabbe connects to the display, to the motherboard and the cable itself.

  • Piper35
    Piper35 Member Posts: 5 New User

    Wish it were that simple.  This is an LED LCD - no inverter.  I'm getting proper voltage on the three test points on the back of the LCD itself which are past the connector.  I wish I could look at the internal setting to see if the IRQ for BKL enable is 'on'.  I'm not suspecting of the cable since I've wiggled it alot to see if intermittantcy is possible.  I would love to see a part layout of the board (already have a schematic) to check 'U' points and resistor levels.

  • philetus
    philetus ACE Posts: 4,759 Pathfinder

    You sure there is no inverter?

    7. Unplug and remove the Acer 7750G Inverter from the LCD.

    http://www.laptopinventory.com/LaptopInventory.php/Acer/Aspire/7750G/LCD

  • Unfortunately, I can find no information whatsoever on your model.

     

    If you are able to get the panel manufacturer and part number from the screen, you should be able to find the data sheet. From that point it is reasonably straight forward to test all connector pins.

     

    If the backlight is the only issue you should be able to confirm data is being displayed by shining a torch on the screen. If your panel does not employ an inverter then, on the face of it, it does suggest power is not getting through and the data sheet will indicate the power pins to test. If those pins appear ok, it does suggest an internal problem which would probably require panel disassembly. However, as you have a replacement screen and both exhibit the same problem I would still suspect a cable problem. I say that simply because the panel did come back to life and, in my experience, this is not at all common where component failure is the cause.

     

    Is it possible for you to bench test your original panel? Can you find the backlight connections/requirements (from the data sheet) and apply the correct voltage/current and see if it works?

    Clearly, I have no way of knowing your ability level so I must stress that any action you take is entirely at your own risk. I am not recommending you do this - that is a decision for you. If your panel does have an inverter (and even if it doesn't), you may expose yourself to high voltages that could kill!!!

     

    Afterthought:
    I assume your model will have a function key to switch video output. It may be worthwhile taking a look at that too (although I would put that low on the list).

  • Piper35
    Piper35 Member Posts: 5 New User

    Positively  NOT a CFL LCD.   Box it came in has " 17.3" HD+Acer CineCrytstal LED LCD."  Hence no inverter.

  • Piper35
    Piper35 Member Posts: 5 New User

    Thanks for the comments.  Yes, the torch works.  It is a Samsung LED unit and had three Voltage test points on it, all good. I was not wanting to spend any more on it ($55 for cable) until I could prove it bad.  It's like good money after bad.  I got over $100 in case parts in it now and since it was working when I started I'm flumxed.   I guess I'll try pulling up a data sheet on the panel and test with voltage after I disassemble it for the 9th time.  Nothing to loose.  BTW, on the MB I found an 'on the board' number of P7YEO _ LA-6911P.  The number I originally listed was on a paper sticker.  Nowhere is there any number with an 'MB' in it???

    PS: The keyboard screen on/off (Fn + F6) has no effect.  The Fn+F5 toggles to the outboard monitor no problem.

  • philetus
    philetus ACE Posts: 4,759 Pathfinder

    MB.RCX02.001