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Monitor Dell M781S Problem

14 Gru 2007 23:34 2660 6
  • Poziom 12  
    Hi all colleagues
    i've this monitor Dell model M781S with Chassis Code DP85 and inside the monitor there's a print on the main board sayes DP17MT , the closest schematic i've found for this monitor was here :


    the original fault was excessive width with no user contorl and the cause traced to Q408 = D2058-Y which was short circuit , this is not a 2SDxxxx but it's a KTD2058 and u can replace it using the standard 2SD2058 or 2SC3691...3851 , the fault with cured by replacing this transistor and the monitor worked fine for more than 3 hours test .
    when i came to collect the monitor back and before closing the back cover i tried to make one more test and surprisingly the monitor didn't work and the power led is not even glowing!!
    dismanteling the monitor again and checked the power supply and found :
    57V@D609 and collector of horizontal output Q404
    the 13V line @ D611 is as low as 10.5V and no 6.3 filament voltage
    there is 5V@ pin 11 of the micon IC201
    does this means a faulty micon?
    any idea what could cause this?
    thanks for any help or tips
    Kind Regards
  • Poziom 12  
    hi again
    well , let me rephrase my problem so that someone can help me :)
    1- the schematic link included is not exactly as my monitor chassis but the closest i've found , if any one know the exact service manual , please upload or tell where to download it .
    2- i have a power supply voltage values printed on the chopper secondry side and they are as follow :
    A- the 6.3V line that comes out of D608 and the actual measured voltage here is 4.99V
    B- the 50V line that comes out of D609 and the actual measured voltage here is 58.1V
    C- the 72V line that comes out of D610 and the actual measured voltage here is 83.1V
    D- the 13V line that comes out of D611 and the actual measured voltage here is 11V
    E- the -12V line that comes out of D612 and the actual measured voltage here is -14.9V

    this is for the power supply lines and checked all semi-conductor components and changed some electrolytics capacitor with no avail .
    3- for the Micon i have Vcc = 5V and i can see the filament of the CRT lit dimmly but the power LED is not lit neither orange nor green or even blinks!
    4- for IC601 i have the following voltages :
    pin 1 = 11V
    pin 2 = 11V
    pin 3 = 0V ( GND)
    pin 4 = 5.37V

    any hints or comments is highly appreciated and thanks for any help
    Kind Regards
  • Poziom 12  
    any help or suggestation?
    does any one has an eprom dump for this monitor please?
    This is a samsung Chassis with micon = S3P8629XZZ-AQB9
  • Poziom 12  
    hi lisek
    thank you very much for help and support :)
    i have the following chassis information :

    1- MCU = S3P8629XZZ-AQB9
    2- Sync Processor = TDA4859PS
    3- FBT = FQB-17A003E
    Rev.02 F
    3- Vertical ouput = KA2142
    4- Eprom = KS24CO4
    5- Power Controle = DP104C
    IC 602 = PQ12RD11
    IC 603 = KIA324P
    IC 604 = KIA7805P

    one more thing i'd like to add , according to this link :


    this monitor should have OSD in case the cable of VGA is disconnected from PC and in my monitor it doesn't do that , if the cable is connected or disconnected i don't have OSD , i'll check the link and will see .
    i just changed Q408 in the E/W circuit and restored normal width and control and the monitor worked fine then dead as i said in my fault
    will try to dump the emprom and feed back , hope it's not the micon
    thanks again :)

    Kind Regards
  • Poziom 12  
    Hi all colleagues
    the monitor has been repaired using another salvaged MCU from a scraped samsung DP17LS chassis and it was actually the microprocessor and not the sync processor as i've replaced the sync processor before trying the MCU and the monitor was still dead , but after replacing the MCU , the monitor worked fine and everything is ok now and here's the dump of this monitor incase some one need it and also has been uploaded to dump database
    thanks for every help given :)
    Kind Regards