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    #1

    Philips no Backlights

    I have a Philips 200W 20" lcd monitor with no backlights. When I power up the monitor the green power light is working (but no display). I connected some working ccfl lamps to see if the problems is with the lamps, The montior has 6 lamps, if I connect all six, then I do not get any light on the lamps but if I only connect 2 lamps (one on each transformer) then thay try to light up, it looks as if there is not enough power to light them up. I am trying to find the data sheet for the backlight driver chip, Not sure where to start I have changed all the caps but still the same.
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    #2
    Re: Philips no Backlights

    Originally posted by terry
    I have a Philips 200W 20" lcd monitor with no backlights. When I power up the monitor the green power light is working (but no display). I connected some working ccfl lamps to see if the problems is with the lamps, The montior has 6 lamps, if I connect all six, then I do not get any light on the lamps but if I only connect 2 lamps (one on each transformer) then thay try to light up, it looks as if there is not enough power to light them up. I am trying to find the data sheet for the backlight driver chip, Not sure where to start I have changed all the caps but still the same.
    Check this out
    http://pdf1.alldatasheet.com/datashe...LD/SI4542.html

    Comment

      #3
      Re: Philips no Backlights

      bobdee you rock dude i think you solved my problem with that all data sheet link for the complimentry mosfet 8 pin ic

      YAY
      School fees paid as everyday is a learning curve.

      Comment

        #4
        Re: Philips no Backlights

        Help please, Is there any way I can test to see if the inverter transformers are ouputing, I can not find the fault on this monitor, not sure if the problem is with the chip or the transformer. The service manual can be found here if any one want to have a look. www.linfotech.co.uk/schematics/philips/Philips 200w6.pdf

        Thanks

        Comment

          #5
          Re: Philips no Backlights

          Originally posted by terry
          Help please, Is there any way I can test to see if the inverter transformers are ouputing, I can not find the fault on this monitor, not sure if the problem is with the chip or the transformer. The service manual can be found here if any one want to have a look. www.linfotech.co.uk/schematics/philips/Philips 200w6.pdf

          Thanks
          The link for the service manual is bad.

          Do you get any hint of back light activity? There are two separate drive circuits for the transformers. The chances of both of them failing is very small.

          There is a 13 pin cable running from the power supply / inverter to the logic card. I will call the red wire pin 1. With the monitor plugged in, check the voltages on pins 2, 3, 4 (pin 11 is ground). Do any of them change when the power button is cycled (pressed twice slowly)?

          PlainBill
          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

          Comment

            #6
            Re: Philips no Backlights

            Hi PlainBill, If you paste the whole link in www.linfotech.co.uk/schematics/philips/Philips 200w6.pdf

            The power and backlight are on the same board. I have connected some tested and working lamps to the board, When you press the power on/off switch the lamp light up about half way and go off. I have checked the power to the inverter drive chips and thats fine, aslo the power voltages to the logic card do not change when starting the monitor( The only pins the change on the logic board are the enable and the dim).

            Comment

              #7
              Re: Philips no Backlights

              I have the same monitor with the same fault.
              Actually it is the second one, as last year I had my original 200W6CS replaced for free just three months before the warranty expire date; the "new" monitor they delivered me lasted just one year and then broke up in the very same way. These products are really quite reliable!!

              Warranty is obviously over, so I got it to an official Philips service center and they told me it is "not repairable" (= throw it away and buy another) because, they said, the inverter is broken and is not available as a spare part.

              Which seems to me quite absurd, considering that we are talking of an only 4 years old product!

              Maybe I'm too old-fashion-minded, but I really can not... swallow the idea of throwing away a nearly new monitor (my previous crt lasted 12 years) which costed me more than 400€ just because some board component maybe worth twenty times less!

              Unfortunately I am not keen in electronic do-it-yourself (testing, soldering and so on), however it seems impossible to me that at least the whole power board can not be found somewhere; it should cost far less than the whole monitor, any way!

              Any suggestions?

              Thank you
              Last edited by armando; 05-30-2010, 10:18 AM.

              Comment

                #8
                Re: Philips no Backlights

                You can start by taking apart the unit and posting pictures like the OP above.

                The members may be able to spot bad caps for you or make suggestions. If you can't solder, it is pretty easy after watching some youtube videos. But if are not comfortable, get a friend to do it.

                Originally posted by armando
                Unfortunately I am not keen in electronic do-it-yourself (testing, soldering and so on)
                Thank you
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                Comment

                  #9
                  Re: Philips no Backlights

                  I also have a Philips 200W6 monitor - it has been in use since 2006.

                  Recently it stopped working abruptly - so changed all but one of the Power Supply Capacitors (the remaining 120uF 450Volt capacitor is meant to be delivered by the end of this month).

                  It is working again but with an intermittent glitch of image distortion triggered by the moment the BIOS screen gets replaced with the Windows 10 log in screen (DVI input resolution changes?) - sometimes the screen loses a couple of inches in a column on the right hand side with the remaining image compressed but otherwise perfect OR only a one inch column showing a highly compressed Windows log in prompt with the rest of the screen entirely black except for that one inch column - either intermittent glitch can be cleared by power cycling the monitor Off & On which immediately produces a perfect picture - which then stays perfect for several days of boot ups and then the glitch comes back!

                  Can anyone help identify the Seven SMD Capacitors on the Logic Board?

                  There are 5 Marked:-

                  "5k
                  47
                  25V"

                  and 2 Marked:-

                  "6a
                  22
                  16V"

                  Do those markings mean 470uF at 25Volts and 220uF at 16Volts? Or perhaps something else?

                  Any ideas what make and model those 7 SMD's are?

                  Have included a Photograph of the Logic Board - intend to swap those 7 SMD capacitors, re-solder the DVI connector and other suspects (suggestions welcome) if changing the remaining PSU Capacitor still leaves the glitch.

                  Will also re-solder the heavier connections on the PSU and the ones factory marked as "Check" on the solder side of the board when I take it out again to fit the remaining capacitor - see the thread starters photo of the back of the PSU PCB.

                  Have posted up before and after Photos of my PSU (I think the thread starters PSU photo is a before photo as the white glue seems intact) - it is noteworthy that the Capacitors I have numbered 3 and 8 are 125 Celsius capacitors the rest all being 105 Celsius capacitors - Looks like Philips changed the capacitor specifications during the production run as it became aware of premature failures. I changed Capacitor 9 to a 125 Celsius version also.

                  Ideas and suggestions for fault finding are welcome.
                  Attached Files
                  Last edited by UHU; 09-02-2016, 06:30 PM.

                  Comment

                    #10
                    Re: Philips no Backlights

                    Those caps would be 47uf/25V & 22uf/16v

                    Comment

                      #11
                      Re: Philips no Backlights

                      Thank you R_J - you were absolutely right about those capacitor values.

                      Took it all apart again to finish the job - it was still working when I disassembled it - just with random bouts of mangled garbage display (but no more missing image) at power on (power cycle to clear) - then discovered the top right hand side (next to PSU) screw holding the Logic Board to chassis was loose and as I had not touched anything else yet tightened it and tried power on - thinking it was only intermittently earthing and that was causing the weird problems (have had similar issues on some odd designs of PSU's) - instead now it is dead as a doornail!

                      A feeling of doom washed over me - how could tightening one screw render a monitor dead? By now couldn't care less.

                      Took it apart and fitted the replacement mains inlet capacitor - finally completing the PSU rebuild.

                      Then removed the Logic Board and changed the seven capacitors, re-flowed the solder on the following parts:- two hefty diodes, all the board edge multi-pin connectors, DVI socket and just for good measure the unused VGA socket.

                      Reassemble and it immediately powers on - seems fine - plug into PC still fine - actually the picture is now so sharp/vivid it is almost too much - literally eye-watering.

                      There I was suspecting I might need glasses for computer screen work - NO my vision is in fact still perfect!

                      Turns out just the monitor logic board capacitors gave a strange intermittent blurriness - like a slight ghosting blur around letters on screen - all gone now.

                      After an initial week of enduring a thermonuclear style of monitor display either I got used to it or the parts/repair burnt in and calmed down.

                      About a month has passed since then and the monitor has not misbehaved or skipped a beat even once.

                      Here are some photographs
                      Attached Files

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