Viewsonic VX2233WM LCD monitor - Page 1
Forum section: electronics / repair

author: buzzawak
author_rank: Contributor
timestamp: April 01, 2019, 05:19:35 am
content: Viewsonic VX2233WM LCD monitor faulty.Symptoms: Monitor turns on (blue power light)Displays for 3 seconds then goes black, power light stays on.Turn the monitor off and on again, repeats 3 second display and goes black, power light stays on.Monitor recognizes when a signal from the computer is present.Resources:Unable to locate circuit diagram.Action: Inspected circuit boards no visual sign of failed components.Replaced all electrolytic capacitors.Advice needed:Next step ?

author: Nusa
author_rank: Super Contributor
timestamp: April 01, 2019, 05:35:04 am
content: My guess is one of the CCFL tubes has failed, and the backlight circuit gives up after a few seconds.

author: tautech
author_rank: Super Contributor
timestamp: April 01, 2019, 05:53:56 am
content: Quote from: Nusa on April 01, 2019, 05:35:04 amFailed yes as in it's drawing too much current and the back light inverter controller chip that monitors current draw then shuts down.Look up the datasheet for the backlight IC and study it to understand the shutdown mechanism.The normal fix is to get a replacement LED backlight strip and it's matching inverter and power it from one of the LV rails.The CCFL inverter can/should be disabled and often it's real easy to do as they can be fed through a jumper link, an inductor or a SMD link.

author: neil
author_rank: Contributor
timestamp: April 01, 2019, 04:37:38 pm
content: How is Brightness and Sleep (switching off backlight) handled with the replacement LED strips? There doesn't appear to be any documentation mentioned in the ads for the LEDs, although they seem to have some sort of connections for Enable and Brightness in addition to their power leads.OTOH, I see inexpensive CCFL tubes advertised on eBay as well - are LED strips preferable to just replacing the fluorescent lamps, given those considerations?I have a MAG 22" monitor with identical symptoms and visibly burnt CCFLs (with blackening at the ends and some local melting of the adjacent plastic light diffuser) so I'm also wondering which way to go.

author: Nusa
author_rank: Super Contributor
timestamp: April 01, 2019, 06:23:35 pm
content: If you decide to replace the CCFL's with new, replace all of them, not just the dead one. The others will likely be near the end of their life as well.Quote from: neil on April 01, 2019, 04:37:38 pmThe one I did (a 22 inch BenQ) had 4 wires as input to the converter board. Vin: 12-30V DC, ENA: enable, DIM: brightness, and Ground. It's up to you to find ENA and DIM signals on your monitors logic board, or you can leave them unconnected for full brightness.As I recall, I got my LED kit from Aliexpress for under $4. Check the feedback and pick a vendor that packages them properly, as the LED strips are easily broken if bent. Mine arrived inside a 2-foot piece of cheap plastic conduit for protection. And I tested them with a lab supply before I confirmed delivery.

author: wraper
author_rank: Unknown
timestamp: April 01, 2019, 06:27:37 pm
content: What happens is protection kicking in, in 95% of cases it happens because of one of these 3 things:1. bad secondary winding of CCFL transformer (each should be around 1k, 2 secondaries in total)2. bad capacitors3. bad ccfl lamp

author: pbarton
author_rank: Frequent Contributor
timestamp: April 01, 2019, 08:23:58 pm
content: There is a single 'Intelligent CCFL Inverter Controller' chip which is monitoring overcurrent on start up, on all tube circuits, hence the screen illuminates for 3 seconds and then closes down in the presence of an overcurrent fault. Typical part numbers include OZ960 and OZ9938. So, you can either....1. identify the failing CCFL transformer or capacitor or CCFL tube, and replace/repair, or2. defeat/overide the Inverter Controller chip (there may be safety considerations) or3. get a replacement LED backlight strip.

author: wraper
author_rank: Unknown
timestamp: April 01, 2019, 08:38:10 pm
content: Quote from: pbarton on April 01, 2019, 08:23:58 pmAnd get crappy bluish image lacking green color.

author: buzzawak
author_rank: Contributor
timestamp: April 01, 2019, 10:04:10 pm
content: Quote from: wraper on April 01, 2019, 08:38:10 pmWraper it sounds like you don't think the LED is the way to go.

author: wraper
author_rank: Unknown
timestamp: April 02, 2019, 12:13:53 am
content: Quote from: buzzawak on April 01, 2019, 10:04:10 pmLEDs for LCD backlight are very different from LEDs you get on LED strips, not to say panels are designed for light source with particular spectra. Regular white LEDs emit basically mix of blue and yellow, blue prevailing. Still, cheap panels, especially early ones somewhat suffer from this issue too. But nowhere close to what you'll get by simply placing led strips instead of CCFL.CCFL:Cheap WLED for LCD:Usual white LED: