Question about ViewSonic A90f+ 19" CRT Monitor

1 Answer

Wavy distortion on bottom of screen

ViewSonic A90f+ 19 in.CRT

I have a horizontal wavy type of distortion on the bottom of my screen. It started on the very bottom and has been growing ever since to the point where it now is taking over almost a quarter of the screen.

I checked the cable, changed computers and all settings.

Does anyone know what this is? I have experience with Guitar amplifiers so I can probably handle it if its fixable. Anyone know what this is?


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  • 9 more comments 
  • donkey22 Feb 02, 2009

    Just to add...

    I know Moire is described as a wavy distortion but this is more like a sea of distortion in which you cant even make out the image underneath.

  • donkey22 Feb 02, 2009

    Hey thanks

    So this kind of mess on the bottom of the screen that grows each month is usually a capacitor shorted?

    It funny ..this monitor was only 3 years old when this happened

  • donkey22 Feb 02, 2009

    One more thing

    If I turn the computer off the monitor keeps powering on and off. I didnt mention this because I though its something to do with my computer settings but maybe its related? This started a few months after the initial problem

  • donkey22 Feb 04, 2009


    The amps I have restored are point to point wiring. I know amps--this is very different. If I had a schematic that would help

    but anyway there are 2 circuit boards.
    Im assuming most problems are on the small circuit board attached to the tube--is this correct?--and are the capacitors I should check on this small board?--and should I desolder these 2 caps check for a short or will these read infinate resistence while on the board?

    thanks guys

  • donkey22 Feb 04, 2009

    The monitor model Viewsonic 19" A90f+
    vcdts23307 made in 2003

    Im gonna open her up tomorrow to get the other info. Is that big cap on the little board connected to the tube?

    Thanks so much

  • donkey22 Feb 06, 2009

    Hey Thanks

    I checked a bunch of stuff but the problem Im having is I cant find a layout diagram for this so Im blind. All the caps I checked are good. They were 100uf/250v , 220/400, 1000/16 which was next to the burnt resistor. The was glue inbetween these 2 so I dont know if the glue heated.

    I took some pictures so maybe someone can give a bearing. You will see the circle where the missing caps I tested were from. There was a burn spot on a 5 ohm reisitor at R384. I think its 5 or 6 ohm--it has a green-gold-gold-gold pattern--which I have never seen(I have never used such low resistors) It tested at 7 ohms

  • donkey22 Feb 06, 2009

    Oh Yeah
    There is little cut in the Z809 under the Big cap on the bootm in the picture

  • donkey22 Feb 06, 2009

    I looked through so many and nothing

    So far I cant find any bad caps

  • donkey22 Feb 08, 2009


    someone said this is a symptom of a vertical IC problem. Can anyone look at the picture and tell me where this is so I can see if the burnt resistor was in this location?

  • donkey22 Feb 18, 2009

    To update
    I replaced the caps around the Vertical IC and the pic filled the screen again. But after a week it seems to be starting all over again ever so slightly. Im thinking it might be the chip

  • Anonymous Mar 13, 2009

    I think I have the same problem. It started about a week ago with just a fewhorizontal quivering lines over the task and its been getting worse. tonight i can only faintly see the image through a cloudy looking covering of lines. I have to right click and wait and see whether I have 'hovered' over the correct icon to do anything.


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  • Master
  • 6,966 Answers

Hi and welcome to FixYa,

Depending on the length of time the monitor has been used, this would often indicate a power supply problem, more specifically a low main B+. Since you are familiar with electronic components & circuitry, you might want to check the big filter capacitor right after the bridge diode on the hotside, likewise the capacitor after the single diode on the secondary side and or the capacitor along the + rail going to the FBT/HOT.

Good luck and thank you for using FixYa.

Posted on Feb 02, 2009

  • 2 more comments 
  • Louie  Role
    Louie Role Feb 04, 2009

    Hi again,

    For some reason, I failed to receive notice of your postback/comments, my apologies for replying rather late then.

    On the monitor, your additional information all points to the big capacitor of the power supply, something like 470uF/160V, that has started to leak and over time lost its ability to filter and store electrical charge. The leak normally takes some time.

    On the amp, it would help if you could postback the brand/model. Capacitors in this type of design (tubes) tend to deteriorate faster because of the heat. Capacitors should always be checked out of circuit and discharged. When using an analog tester, the capacitor should show the needle deflect towards the right and then slowly go back to the left. Reversing the test prods would show the same.

    If the brand/model could not be determined or if no schematics are available, you could get the tube numbers (something 4BA6), the spec sheet could be Googled and the voltages normally applied to each pin could be determined. Thereafter, measuring the voltages on these points while referencing the spec sheet would give you an idea if the bleeder/bias resistor supplying the voltage needs further investigation by the presence or absence of the volts. In some instances, removing the tubes and cleaning the pins would correct some problems.

    Am curious so would appreciate an update.


  • Louie  Role
    Louie Role Feb 04, 2009

    Honestly I got mixed up. I though the first part of your recent post was about the monitor and that the second part was about a vacuum tube amplifier, LOL, gotta layoff the coffee.

    Anyway back to your concern on the monitor. The smaller PCB right at the rear of the tube has nothing to do with the bottom wavy line. That smaller squarish board with shielding is for the color drive transistors/IC. If the display is missing a color, fault would be in this board.

    The bigger bottom board is the main board. If you would follow the AC power cord, it would lead you to a bridge diode then to the big filter capacitor. This would be the primary hot side. From the capacitor, it would go to a power pack IC that does the regulation switch mode, then to a small transformer. This is a high frequency high power transformer. The secondary side of the transformer would lead you to single diodes and slightly smaller capacitors.

    Foremost to check would be the primary capacitor after the bridge diode.

  • Louie  Role
    Louie Role Feb 06, 2009

    This page has about 200+ schematic diagrams of Viewsonic models but none exactly for an A90F+. What could be tried is to download is a schematic for a 17 or 21 inch whose chassis is identical to the A90F. Unfortunately due to limited bandwidth I am unable to do this. Additionally, some other brands like AOC shares the same chassis as the Viewsonic.

  • Louie  Role
    Louie Role Feb 18, 2009

    Appreciate the updates. Might be the vertical IC, one indication is if it heats so much that it could not be touched.


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