Help: TV/Monitor Samsung Syncmaster 2033HD problem

[XpsikotiX]

Hello,
My monitor crapped on me so i cracked open and see what went wrong...
What are the symptoms:
Blank screen - the backlight is not lighting up
No sound -  i don't really think is a faulty ,just doesn't' have input signal
The blue led from front panel is lighting as it should , i can turn on and off the TV with the remote.
I measured the power supply and all the voltages for the main board are nominal , but i have no voltage for the backlight - 700v
All the caps seem fine, also checked them with a multimeter and the capacity is ok.
power supply model : PWI2204ST
Can anyone that works in the domain can help me if this is a common issue?
Any suggestions?

[w2aew]

I don't know about that specific model, but there is often a separate inverter power supply board for the backlight.  The few that I have repaired had a shorted transistor or two, which opened an SMD fuse. Failure was initiated by dried up electrolytic caps on the same board.

[KarlMonster]

I don't have direct knowledge of your model, but I'll share what I learned from fixing my 8(??) year old ViewSonic that had gone very, very dim.

I approached the scenario that my dark screen was either from bad display, or from no backlight. Some LCD units have the lighting inside the LCD display unit, in which case, I'd get a new monitor - and I did anyway. If your backlighting is in the form or cold cathode ray tubes, then they need a very specific minimum voltage to light up. This voltage may be specific to your unit.

In my case, I needed to have about 400 volts to start the Cold cathodes, but I was reading only about 99 and 96. After some examination, I realized that my monitor effectively had 3 separate voltage zones across at least two PCBs, with any two separate voltages maintained by a pair of film radial caps. I have little faith in that type of cap, and replaced them with higher value caps, which completely solved the problem. I don't remember clearly, but at the time I don't believe that I confirmed that the original caps were bad, I just went ahead and replaced them. I simply treat those caps with great suspicion, and it made sense that IF the correct voltage differences were not being maintained across three different voltage zones, then of course the inverter - in the third zone - wasn't going to have nearly enough juice.

Also I should add that my monitor had slowly grown dimmer and dimmer and dimmer, which should also have cued me in on the bad caps.

If you are getting ZERO volts at your back light, then find where the voltage trail ends. You may also be getting zero volts at your audio circuitry.

[XpsikotiX]

There are no bad caps unfortunately ... the monitor has like 40 hours of use but no warranty . Every thing looks brand new inside : no signs of overheated components, no blown components , no dust ... nothing....
I will take it to a service repair center to see what went wrong .
Thank you for your support

[wraper]

Check the secondary windings of the inverter transformer. Resistance should be around 1k. If transformer is ok, then check if inverter trying to work at all with oscilloscope on transformer primary. But must do it at the moment of switching on, as after 1-2 seconds inverter will shut down because protection will kick in. If one transformer winding winding or backlight bulb is dead, backlight usually appears for a short moment until protection kicks in. So there might be also that inverter mosfets, driver IC are dead if it does not light at all. Also check fuse F201 on the inverter power rail.

[wraper]

There are no bad caps unfortunately ... the monitor has like 40 hours of use but no warranty . Every thing looks brand new inside : no signs of overheated components, no blown components , no dust ... nothing....
I will take it to a service repair center to see what went wrong .
Thank you for your support

I doubt this is economical in Italy.

[Redcat]

I just finally repaired an old Fujitsu Siemens 19 inch Monitor (because it has a very nice image and I wanted to keep it) last week at work and maybe it could help you:
Actually I "repaired" it 3 times  .
First 2 electrolytic caps on the secondary rail were blown. I changed them and the Monitor worked for 2 weeks. Then nothing worked.
I took it back home and changed the other caps. I hooked it to my private computer as second monitor (for stability test), but it worked only for another day. But next day back at work, the monitor was going on and off and on and off, only showing the start logo for half a second.
What can I say  , took it back home, changed all other electrolytics I hadn't changed and tested almost all components on the main power supply.
All fine. But... during this I red, that it could be the ccfl backlight transformers ( or the controller chip, which went to protection mode).
I desoldered the one of the two transformers out which was suspicious to me... and it worked again  .
I measured the transformer and...no shortcuts.
Hmmm...there was only one component near the transformer left and this was a blue polypropylene capacitor.
Capacitance was good, but showed no esr value - the other blue PP cap showed both.
I bodged in a new one (actually a bigger old one from my parts bin) in place of this cap and soldered the transformer back in.
And now the Monitor is back to life for a good week without any problems  and I think it will be good.
Be careful with the high ccfl voltages and the big input cap   .
I would never have suspected the lil cap, so check really everything, all the lower power supply output voltages and components around the ccfl transformers.
I hope this little story helps you and good luck  , Tom

[XpsikotiX]

Thank you guys for the info, i will check all the tips that you gave me and see if applies to me. I did not have any time this week to take it to a service, so i will give it another try.