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[Taxi_Driver]

My Dell 19" LCD monitor on my desktop decided to turn itself off the other day....and wont come back on....i suspect it maybe the power supply. It doesnt have an external power supply, the mains cable plugs into the monitor.
If it was an analogue monitor i would probably chuck it and get another....but its a digital input one.....and gives really sharp image even at 1280x1024.....and was a few dollars.....yes erm dollars.....i bought it from the usa bout 4 years ago.

You can hear the mains arc as you plug the mains cable in.....which its always done....so suggests the primary side of the psu is taking power....the green power led doesnt come on tho.....and as its got membrane switches for all the controls including on/off , i guess a logic circuit could have gone and its not the power supply :-/

Im gonna have the back off it tonight.....any ideas peeps?

[Danny]

does that mean it doesnt have its own fuse?

these days not much in the way of technology lasts too far beyond warranty, might it just have died its death?

[CaptainZok]

Careful round that psu TD those things bite even when disconnected, trust me I speak from experience.

[pete1666]

I`m no expert but the onboard power supply failing is a common fault on LCD`s,
also check if it has a fuse inside near ths power supply.

[TheBoy]

It will be a smps, they can be a bugger to fix when not working

[CaptainZok]

Dried up PSU capacitors are a common fault IIRC.

[TheBoy]

Dried up PSU capacitors are a common fault IIRC.

Yup, though, esp with smps, when they dry up and fail, further damage to the psu may happen...

[Marks DTM Calib]

Yup, sounds like the primary side may be at fault......generaly, the led lights otehrwise and on some models will flash a code sequence to indicqate what rail is down.

Not much to the primary side.....a rectifier to get a nice chunky 325V DC (be VERY careful of this as the smoothing cap stores it for some time on some models). A chopper setup to chop the HV DC into a high frequency square wave to feed into the switching transformer (high speed means less iron required and hence a smaller and lighter transformer).

There will then be some control circuitry which varies greatly and normaly includes an opto or small transformer for feedback across the safety barrier (secondary to primary).

[Taxi_Driver]

Careful round that psu TD those things bite even when disconnected, trust me I speak from experience.

I will be careful....dont worry....many moons ago i used to tweak 24" CRT's (as part of my job and the biggest crt you could get then  ) adusting H & V axis as well as curvature.....my boss then like to see a nice square image and not overlapping the outer edges like tv's do. I never killed myself then  

[CaptainZok]

Careful round that psu TD those things bite even when disconnected, trust me I speak from experience.

I will be careful....dont worry....many moons ago i used to tweak 24" CRT's (as part of my job and the biggest crt you could get then  ) adusting H & V axis as well as curvature.....my boss then like to see a nice square image and not overlapping the outer edges like tv's do. I never killed myself then  

Hope you kept one hand in yer pocket like a good little tv repair man.

[Kevin Wood]

Another fault I've seen is the inverters for the cold cathode backlights. These have voltage and current monitoring circuits and will crowbar everything if they go out of spec. Sometimes if you can isolate the supply to this part of the circuit you can verify that the main SMPS is working.

Kevin

[Ken T]

Another thing to check is the SMPS controller chip supply. They used to generate this by tapping into that nice 325V DC supply and using a 100K-200K resistor to provide the VCC for the controller chip. Trouble was they used to use general resistors rated at 100V which didn't like the 325V across them, so they tended to wear out kind of soon, just after the guarantee expired !. I kind of think its the PSU gone awol, if something else later on was duff, you would still get the front panel LED. If the voltage is high, keep one hand in your pocket, if really high keep both hands in your  pockets!

[Markjay]

Dried up PSU capacitors are a common fault IIRC.

Yup, though, esp with smps, when they dry up and fail, further damage to the psu may happen...

Are these the ones that used to blow up with a bang filling the PSU with white fluffy stuff and making horrible burnt stench?

[Taxi_Driver]

Found the fault......

There was only 4ohms between the VCC rail and ground

It was this causing it.......

http://www.datasheetcatalog.com/datasheets_pdf/I/C/E/2/ICE2AS01.shtml

Cut pin6 and VCC rail to ground is over 5Mohms now  

Just gotta replace it now....

And i didnt kill myself