View original (French)

Benq screen won't turn on anymore

Solved
20156 -  
ecomptan Posted messages 7 Status Member -
Hello,

well, my BenQ T905 monitor won't turn on anymore. For the past few days, I had to press the on/off button a few times because it wouldn't turn on directly. But after that, it worked just fine. But now, nothing at all :(
The LED doesn't light up either. I opened it up to check for any dust or something that might be causing a bad connection, but the screen still won't turn on.
If anyone has any idea?? Is the monitor fried??

Thanks

18 answers

  1.
    20156 Posted messages 81 Status Member 4
     
    Hi Mushu14 and thank you for your help!

    I'm attaching some photos because I really don't know how to recognize good or faulty components...

    Uh!!!!! I must not be awake, but how do you insert a photo here???
    Thanks :)
    3
  2. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    Well, the capacitors seem fine at a glance, but we should still be able to test them with a capacitance meter.
    Otherwise, the common failure with the BenQ is the transistors and the fuse (but if the fuse blows, it's due to the transistors).
    http://www.cijoint.fr/cjlink.php?file=cj201001/cij6PSGyAa.jpg
    (in red the transistors, in green the fuse)
    Depending on the reference, you can easily find them on eBay.
    https://www.ebay.fr/sch/i.html?_from=R40&_nkw=C5707&_sacat_sel=See-All-Categories&_trksid=m38

    To start, you need to test the fuse (without power) with a multimeter to see if it’s blown or not.

    Be careful though, there's 400V charged in the big capacitor and even more on the coils side.
    --
    The return......
    2
  3. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    That's the problem with an ohmmeter, it doesn't give the capacitance
    but keep in mind that if they're swollen, it's because they're failing or have already failed

    Can you check if you have around 300 V DC going through your big capacitor?
    Just be careful not to electrocute yourself, it hurts very, very, very much
    --
    the return......
    1
  4. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    Hi,
    probably 1 or 2 dead capacitors
    when you disassembled it, did you see any swollen ones?
    otherwise, post some photos
    --
    the return......
    0
  6. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    We don't insert photos on CCM, you host them and paste the link
    --
    the return......
    0
  8. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    I have to move, I'll be back tonight
    --
    the return......
    0
  9. 20156 Posted messages 81 Status Member 4
     
    Wow !! Thank you for your quick responses!
    I'll see if I can find these machines to test the things. I'm not sure I'll find them...
    Anyway, I'll keep you posted
    See you later :)
    0
  10. 20156 Posted messages 81 Status Member 4
     
    It's fixed now!!
    But the problem wasn't where we thought it would be.
    It was just a solder joint that had come loose on the board at the socket!!! Just that... it goes to show that you should look a little before throwing it away and buying a new one ;)
    Thanks, mushu14, for your help.
    0
  11. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    content for you and looking forward to it :-)
    --
    the return......
    0
    1. ecomptan Posted messages 7 Status Member
       
      Hello
      I searched Google for repair Benq T905 and ended up on a discussion in the hardware forum...
      I have a screen of this type where the LED went from green to orange... but after changing the capacitor 0.22UF 275V to a 0.22UF 650V, the LED remains off!!!! Yet I checked the solder joints and the component???
      Connected to 220V, the rectifier delivers 1.8V DC (terminals + and - at the ends)!!! Do the middle terminals receive alternating or direct current?? ...I have a value of 30V AC but strangely if I reverse the + and - I get nothing???
      Can you help me??? Thanks
      0
  12. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    Hi ecomptan,

    Can I have a photo of the capacitors?
    0.22µF seems like a strange value, isn't it 22 or 220 µF instead?

    The rectifier bridge does receive alternating current on the middle pins, and if you have 1.8 V in direct output, something is wrong

    Desolder the diode bridge and test it
    Did you pay attention to the polarity of the capacitor you changed?
    --
    the return......
    0
    1. ecomptan Posted messages 7 Status Member
       
      Hello
      First of all, thank you for the quick response...
      I took a picture with my mobile phone (sorry for the quality... I hope it's enough!!!)
      https://www.cjoint.com/?dbngpAwdnw
      I scanned the 0.22uF capacitor that I replaced with the red one in the picture... I don't think this type of capacitor has polarity...
      https://www.cjoint.com/?cBxNt3p511
      How do you test a diode bridge???
      I’m waiting for your information and suggestions.
      See you soon
      Alain
      0
  13. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    The capacitors circled in red seem swollen, if that's the case they need to be replaced.
    https://www.cjoint.com/?cCaMulilkk

    To test the diode bridge (or Graetz bridge) follow the link (it's on page 4).
    http://the.nerv.free.fr/docpro/test_transistors.pdf
    http://www.premiumorange.com/daniel.robert9/Digit/images/Pont_redresseur_et_son_schema_interne.gif

    But in my opinion the diode bridge was dead, your fuse would have already blown.
    --
    The return......
    0
  14. ecomptan Posted messages 7 Status Member
     
    Hello again

    I haven't been able to work on the printed circuit board this week. I only have the weekend... sorry.
    I just unsoldered the diode bridge 541A 2KBP06M and according to the documentation you sent me, it's fine, so fuse good = bridge okay. How come I have 30V AC and 1.8 VDC??? What values should I have???
    Could it be from the transformer (or coil with 4 pins) ref 19 452025 011 located before???
    As for the capacitors, I changed one (I don't have replacements for the others) but I tested them by unsoldering (with an ohmmeter alternating + and - it charges and discharges normally, now I don't know if the capacity is good!!)
    Thanks for your info
    Alain
    0
  15. ecomptan Posted messages 7 Status Member
     
    I just re-soldered the diode bridge and measured across the terminals of the big capacitor; I find 4 to 5 V DC... far from 300, there’s really a problem!!!
    See you soon
    0
  16. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    well, all you have to do is follow the trail and test the different components
    one thing's for sure, it's in the primary (before the big capacitor)
    --
    the return......
    0
  17. ecomptan Posted messages 7 Status Member
     
    Ok, but where to start.. how to test coils (with the ohmmeter to see if there's a short circuit or an open circuit)???
    0
  18. mushu14 Posted messages 11897 Registration date   Status Contributor Last intervention   1 123
     
    Absolutely, start with that
    anyway, there aren't that many components in the primary, so you'll quickly get a handle on it
    also check the solder joints and the condition of the tracks
    --
    the return......
    0
  19. ecomptan Posted messages 7 Status Member
     
    Well, I'm going to get started, and I'll keep you posted... haha, not in amps
    Thanks
    0