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Thread: PC monitor repair question

  1. #1
    Flashaholic*
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    Default PC monitor repair question

    A friend and I both bought Viewsonic PF790 CRT monitors, nearly five years ago. Beautiful Trinitron picture and mine is still in use today. Her's will not hold the brightness/contrast settings. Whenever the power is cycled on the monitor or the PC reboots, it reverts to quite dark contrast/brightness settings. You can then adjust them back up via the digital controls but it will only hold them to the next reboot or power cycle. Do these monitors have a battery to hold the settings much like a pc motherboard has a battery to hold the cmos settings? I'm sure at today's replacement costs, it's not worth trying to get repaired via Viewsonic. Any ideas?

  2. #2
    Flashaholic* DarkLight's Avatar
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    Default Re: PC monitor repair question

    Buy a new one.

    You can get new one for 200 in 19inches..

  3. #3
    Flashaholic*
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    Default Re: PC monitor repair question

    geepondy,
    I have the same monitor you use, it is a "secondary" monitor now I a 19" LCD took its place. Not sure about the monitor but there might be a work around.
    Go to your video card drivers under the advanced tab and boost the video card settings to see if that will work. My ATI drivers can be boosted to rediculous levels... worth a try. Good luck!

  4. #4
    Flashaholic*
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    Default Re: PC monitor repair question

    Well I took it apart tonight. If there's a flash memory, NVRAM, battery or someother method of storing the settings, it isn't readily apparent but there must obviously be a way. I think I'll try to do a good search.

  5. #5
    Flashaholic
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    Default Re: PC monitor repair question

    G,
    Some things to consider. Most CRT monitors over two years old need help.

    Electrolytic caps used in them start to dry out. When that happens they loose efficency. Most people see it on start up where the monitors don't start well, or 'click' as the circuits try and kick over.

    Also the caps near the flyback tend to 'fry' in the heat. These are filtering various DC's that are not smooth waves, so as the caps get old, their ability to filter also suffers.

    I use an ESR (Equilivent Series Resistance) tester and a marking pen to check caps. I fully power down the monitor and using the ESR tester probes like chop sticks start to probe the caps in circuit. On units I don't like the reading of, I color in the tops of the caps with the marking pen for later changing.

    The ESR meter makes a small signal of about 3mv at 100khz and translates that into an equilivent 'ohms' reading. So if all works well it will read the just the cap your probing and tell you in general terms what it's internal state is. Not it's value in uF's.

    A new 1uF cap will usually show less than one ohm. A failed one will show usually five or more ohms ESR. So if I get a 220uF or 1000uF and it shows me any resistance, I know it's a failed unit.

    About the 'memmory' in the monitor, you might want to look for a 'gold cap'. This is a class of device that are used to back up sold state memmories. If you look at the values you will see numbers like 1F. Huge caps in a small space. These die too. They operate like small batteries and the chemicals in them tend to erode the internal parts. In Uniden radios I used to change this part on a regular basis because if it hasen't failed yet, it was going to. Mouser used to sell them.

    So look for a gold and black cap with an odd value and you will most likely find the memmory keep alive for your values.

    Consult with some of the other tech guys here, they are sharp dudes.

    Hope I diden't put you to sleep.

  6. #6
    Flashaholic* turbodog's Avatar
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    Default Re: PC monitor repair question

    [ QUOTE ]
    geepondy said:
    A friend and I both bought Viewsonic PF790 CRT monitors, nearly five years ago. Beautiful Trinitron picture and mine is still in use today. Her's will not hold the brightness/contrast settings. Whenever the power is cycled on the monitor or the PC reboots, it reverts to quite dark contrast/brightness settings. You can then adjust them back up via the digital controls but it will only hold them to the next reboot or power cycle. Do these monitors have a battery to hold the settings much like a pc motherboard has a battery to hold the cmos settings? I'm sure at today's replacement costs, it's not worth trying to get repaired via Viewsonic. Any ideas?

    [/ QUOTE ]

    I think VS had a bad run of monitors about this time. I had about 8 of these models and half of them failed early. I'm a die hard VS fan though..... they were all replaced w/o any problems, and VS even provided return shipping labels for some.

  7. #7
    Flashaholic* Negeltu's Avatar
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    Default Re: PC monitor repair question

    Watch out for those caps...

  8. #8
    Flashaholic* snakebite's Avatar
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    Default Re: PC monitor repair question

    force a hard reset.
    those use a small eeprom for user setting storage.forcing a reset may fix it.
    if not there is a way to re init the eeprom from the service menu but the average joe can get in over their head there.
    iirc that unit has a capetronics chassis.viewsonic just rebadges monitors and pastes on the little birds;-)
    they range from taiwan/china cheapies to panasonics .

  9. #9
    Flashaholic*
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    Default Re: PC monitor repair question

    there must be a battery or a little .1 farad(or so) memory back up power source.

    unless it uses something like nv ram - then something is glitching and clearing it.


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