Viewsonic VX924 monitor SMPS failed. Replaced all bad capacitors and have found that one pair of inverter driver transistors has failed. They are marked as DKQR (They are apparently Rohm 2SC4672 transistors). What could have caused the failure? Do you have a circuit diagram for this SMPS/inverter board?

Look for bad caps as shown in my pictures here: http://s807.photobucket.com/albums/yy352/budm/Viewsonic%20VX924/

If you are going to DIY and already try the monitor with another PC, and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply (they should be replaced in a set), blown fuses; poor solder joints, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed monitors to get some ideas what to look for: http://s807.photobucket.com/albums/yy352/budm/
Post back what you see inside so we can guide you further and it will help out other people in the future also.

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r7406380-tv_training_manuals
Failed TV and Monitors: http://s807.photobucket.com/albums/yy352/budm/

Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague

Capacitors kit: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.

Or www.digikey.com just make sure to use caps with low ESR, 105c, high ripple current, long life rating such as PANASONIC FM or FC series.
Please leave rating if it helps.

Here is the service manual: http://ftpkuban.com/FTP/Manual/ViewSonic/va712-2_sm.pdf
You need to verify that you do have steady 5vdc and 12vdc first, the problem can be due to bad caps, failed transistors/IC or inverter transformers, or worst cas the lamp assemblies.
If you are going to DIY and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply (they should be replaced in a set), blown fuses; poor solder joints, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed monitors to get some ideas what to look for: http://s807.photobucket.com/home/budm/allalbums
Post back what you see inside so we can guide you further and it will help out other people in the future also.

http://en.wikipedia.org/wiki/Capacitor_plague
Capacitors kit: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.

Look for bad caps: http://s807.photobucket.com/albums/yy352/budm/Viewsonic%20VX924/

Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx

If you are going to DIY and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply, blown fuses; poor solder joints, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed monitors to get some ideas what to look for: http://s807.photobucket.com/home/budm/allalbums
Post back what you see inside so we can guide you further and it will help out other people in the future also.
http://en.wikipedia.org/wiki/Capacitor_plague

More likely the power supply/inverter board may have failed due to bad DC caps which happen after about 2~3 years.
http://www.shopjimmy.com/power-supply-unit-200-000-170dtlbmh-from-viewsonic-va1930wm-2.htm

If you are going to DIY and have proper tools and know safety precaution then please read on:
Most common failures in the LCD monitors are bad capacitors (bulging top/seal or leaking) in the power supply, blown fuses; poor solder joints, failed inverter circuits (blown fuse, shorted transistors, shorted/open transformers), bad lamps (poor solder connections or worn out lamps). You will need to open it up and inspect the inside, see example of failed Viewsonic and all others monitors to get some ideas what to look for: http://s807.photobucket.com/home/budm/allalbums
Post back what you see inside so we can guide you further and it will help out other people in the future also.
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.badcaps.net
Capacitors kit: http://lcdalternatives.auctivacommerce.com/

My VX924 did the same thing but now displays nothing and power switch light just blinks. According to an answer listed on previous page, it may have bad capacitors. I may have to take a look at them. Viewsonic repair facility examination of this monitor runs $70.

Hello,

If youcan take a picture or two of the boards in your system as close and clear as you can and go to our web page and email them to me I will check and see if we can help you find the problem.

Buddy
Corporate Computer
www.ccl-la.com

See ebay item 390074135923
http://cgi.ebay.com/2-Inverter-transistor-viewsonic-VX910-VX924-DK-QB-QO-QA_W0QQitemZ390074135923
Fran

Hey Brandon.
Besides those transistors, you may also fine the large capacitor adjacent to the transformer gone too, Possibly the transformer may be bad too ?
Also the 924s used at least two style boards.

This is a generic symptom that could happen to any LCD monitor.
The following is a generic answer applicable to most.

The most possible causes are bad capacitors or a bad semi-conductor.

Open the unit and check to see if any of the capacitors in the power supply or other boards look domed or vented on the top.

Replace any capacitors accordingly. Use the same value capacitors. Most often, 1000uF 16V or 25V, 470uF at 16 or 25V, 220uF at 16V or 25V.

If this doesn’t solve the problem, try checking the surface-mount transistors on the inverter board that run the lights. Some times these transistors go bad and can cause the power to cycle up and down. Check the area for any cracked or overheated ceramic or mylar capacitors.

Don’t forget to check for caps on the main board. Some times these boards are overly simple and only have a couple of caps, but other times they are teaming with them.

This is a generic symptom that could happen to any LCD monitor.
The following is a generic answer applicable to most.

Two possible causes are bad capacitors or a bad light inside the LCD panel.

Open the unit and check to see if any of the capacitors in the power supply or other boards look domed or vented on the top.

Replace any capacitors accordingly. Use the same value capacitors. Most often, 1000uF 16V or 25V, 470uF at 16 or 25V, 220uF at 16V or 25V.

If this doesn’t solve the problem, try checking the surface-mount transistors on the inverter board that run the lights. Some times these transistors go bad. Check the area for any cracked or overheated ceramic or mylar capacitors.
Also, you may have a bad light inside the panel. This is tough to test without a spare light to use for troubleshooting.

You can take the panel apart and inspect the lamps but it is very tedious. It's tough enough to get them apart and back together again never mind keeping the layers clean. You have to try not to get any dust between the layers or you will see it in the picture.

There are usually two light fixtures each of which holds two lamps. One fixture is at the top and one at the bottom. Remove them one at a time and inspect the lamps to see if any are broken or very dark on the ends. If one looks out of place, it could be bad.

You'll have to find replacement lights on the net. It's not easy to replace them, but if you've gone this far, good luck. You should be able to get generic instructions off of the site that sells the lamps.