Viewsonic VX2233WM LCD monitor

[buzzawak]

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 ?

[Nusa]

My guess is one of the CCFL tubes has failed, and the backlight circuit gives up after a few seconds.

[tautech]

My guess is one of the CCFL tubes has failed, and the backlight circuit gives up after a few seconds.

Failed 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.

[neil]

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.

[Nusa]

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.

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.

The 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.

[wraper]

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 capacitors
3. bad ccfl lamp

[pbarton]

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, or
2. defeat/overide the Inverter Controller chip (there may be safety considerations) or
3. get a replacement LED backlight strip.

[wraper]

3. get a replacement LED backlight strip.

And get crappy bluish image lacking green color.

[buzzawak]

3. get a replacement LED backlight strip.

And get crappy bluish image lacking green color.

Wraper it sounds like you don't think the LED is the way to go.

[wraper]

3. get a replacement LED backlight strip.

And get crappy bluish image lacking green color.

Wraper it sounds like you don't think the LED is the way to go.

LEDs 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: