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    #1

    ViewSonic Optiquest Q191wb

    I recently was given a broken ViewSonic flat panel monitor. Specifically a ViewSonic Optiquest Q191wb, model number VS11584. It's a 19" widescreen LCD monitor with CCFL backlighting. The reported problem was the monitor would not turn on.

    Step 1 was to open the monitor up. This ended up being more difficult than I had expected. Like so many monitors of this size it's held together by plastic tabs around the edge. But these tabs were very difficult to pop open. I ended up making a few minor scratches in the plastic as I pried it apart.

    Once open the monitor looks like every other monitor, the video board is on the right and the power/inverter board is on the left underneath some metal shielding. After I removed the shielding I immediately noticed a bulging capacitor. I ended up replacing the following 4 capacitors:

    C802 470uF/50V
    C817 1000uF/16V (obvious bulge on top)
    C819 680uF/16V
    C904 220uF/50V

    After acquiring the replacement caps I began the repair. I removed each capacitor, soldered in the replacement, and then tested the old capacitors using my multimeter. I know, I should probably test them first that way I don't replace good caps, but I figure caps are cheap and I'd rather not have to repair this monitor a second time. So I just went ahead and replaced all four. Unfortunately, my capacitor tester cannot handle electrolytic capacitors above about 500uF, so I could only test two of the capacitors. Here's what I found:

    Location | Rating | Measured Capacitance | Comments
    C802 | 470uF/50V | 433uF | Probably bad, 433 is only 92% the rated value
    C817 | 1000uF16V | na | Unable to test, but was bulging
    C819 | 680uF16V | na | Unable to test, probably was still good
    C904 | 220uF50V | 219 | Most likely still good

    I used the following replacement parts from Digikey (part numbers are Digikey part numbers):

    Panasonic EB series 470uF/50V - P13134-ND
    Panasonic EB series 1000uF/16V - P13119-ND
    Panasonic FR series 680uF/16V - P14395-ND
    Panasonic EB series 220uF/50V - P13131-ND

    Digikey is great. Parts were $2.86 plus a couple of bucks for standard USPS delivery. Parts arrived in 2 days.

    After soldering in the new caps the monitor works perfectly! So for less than $5 and about 5 minutes of actual work time I have a working widescreen monitor. Thanks to all the members on this forum. Everything I've learned reading other posts helped this repair to go smoothly.

    Hopefully this post will help others who might be experiencing problems with their Q191wb monitor.
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    #2
    Re: ViewSonic Optiquest Q191wb

    Good Job, I have found that Viewsonics are one of my favorites to fix. Most of the time it is the cheap caps.

    Comment

      #3
      Re: ViewSonic Optiquest Q191wb

      Originally posted by Freezer View Post
      I know, I should probably test them first that way I don't replace good caps, but I figure caps are cheap and I'd rather not have to repair this monitor a second time..
      You missed replacing C824. It plays an important role in the SMPS startup process.

      No multimeter I know of measures ESR (ohms). Low ESR caps are required in the SMPS application.
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        #4
        Re: ViewSonic Optiquest Q191wb

        Originally posted by retiredcaps View Post
        You missed replacing C824. It plays an important role in the SMPS startup process.
        Hmm, I intentionally left that one alone because in my admittedly limited experience small caps like this are never the problematic ones. But maybe I should just replace it to be thorough.

        I am seriously considering ordering the Blue ESR Meter kit. At which point I'll be able to truly test caps.

        Comment

          #5
          Re: ViewSonic Optiquest Q191wb

          Originally posted by Freezer View Post
          Hmm, I intentionally left that one alone because in my admittedly limited experience small caps like this are never the problematic ones.
          That small startup cap has been responsible for many problems here on the board (including some first hand experience). It costs around 33 cents for a Panasonic FM or FC cap so it is a no brainer to replace.
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            #6
            Re: ViewSonic Optiquest Q191wb

            I wanted to post a followup with more information. On retiredcaps suggestion I went ahead and replaced cap C824. I also recently built the Blue ESR kit, so I went back and tested all the caps I removed. Here's what I found:

            Location | Rating | Measured Capacitance | ESR | Comments
            C802 | 470uF/50V | 433uF | .04 | Low capacitance but ESR was fine, possibly dying
            C817 | 1000uF16V | na | 1.3 | High ESR, bad cap
            C819 | 680uF16V | na | .03
            C904 | 220uF50V | 219 | .06
            C824 | 10uF50V | 9.5 | 2.5

            Also, all the original caps were CapXon brand, known to cause lots of problems. Again, I hope this info helps someone else.

            Comment

              #7
              Re: ViewSonic Optiquest Q191wb

              For your C802,rember that the majority of electrolytic caps are plus or minus 20%,so in fact it would be within spec !!

              Comment

                #8
                Re: ViewSonic Optiquest Q191wb

                Originally posted by Freezer View Post
                On retiredcaps suggestion I went ahead and replaced cap C824.

                Location | Rating | Measured Capacitance | ESR | Comments

                C824 | 10uF50V | 9.5 | 2.5
                The Panasonic FC ESR is 1.3 ohms according to

                http://search.digikey.com/scripts/Dk...name=P10316-ND

                I think for the extra 33 cents and the fact that the Capxon caps are 5 years old, it was a good choice to replace the Capxon cap.
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                  #9
                  Re: ViewSonic Optiquest Q191wb

                  Originally posted by retiredcaps View Post
                  The Panasonic FC ESR is 1.3 ohms according to

                  http://search.digikey.com/scripts/Dk...name=P10316-ND
                  I'm glad you mentioned this. I noticed on Digikey's site, very few caps have an ESR value, but they do have an impedance in ohms which is what you quoted. Are ESR and impedance the same, or at least for our needs can they be considered the same?

                  Comment

                    #10
                    Re: ViewSonic Optiquest Q191wb

                    Originally posted by Freezer View Post
                    Are ESR and impedance the same, or at least for our needs can they be considered the same?
                    Basiclly yes.
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                      #11
                      Re: ViewSonic Optiquest Q191wb

                      another little tip: look for the cap datasheets on google.

                      for example searching for "panasonic fc filetype:pdf"
                      ... and the first result is the FC datasheet

                      "filetype:pdf" tells google to only show pdf's and nothing else.
                      the only thing you need to watch out for is that the pdf should be from the manufacturer's website and not some random other site (because they might be outdated)
                      Last edited by Scenic; 04-19-2011, 02:22 PM.

                      Comment

                        #12
                        Re: ViewSonic Optiquest Q191wb

                        Digikey also has the same datasheets linked on their site. That is, their links point to the Panasonic website.
                        Last edited by retiredcaps; 04-19-2011, 02:35 PM.
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