21" Cinema went dead in storage

[CelGen]

When I got this monitor at first it had one dead blacklight inverter but it did work. I put it into storage for six months and now when I try to use it (prior to me spending the afternoon opening it to replace the inverter coil) the thing is dead to the world. The power button is useless and when the G5 is powered on from its power button the monitor displays nothing and the power lamp for the display does not even light. no power over USB either. It's like it's not even plugged in....even though it is.

 

[CelGen]

Missed the edit cutoff.

I stand corrected and yes there is actually +5v going to both USB ports ( I just was not testing using something that immediately showed life when plugged in. )

I can also find +24.7v DC leaving the video card (5200FX for testing reasons) in pins 1 and 2.

Okay, I'll start a teardown and see what's going on inside....

 

[CelGen]

Huh, very odd.

I opened it up and it seems a surface mount coil fell off. It was easily soldered abck on and the monitor came back to life.

The inverter on the other hand is not going to be as easy....

Well at least I know what the problem is. Unfortunately the inverter boards I have are not actually for my model cinema display. :-/

 

[techknight]

And unfortunately, that "burn" makes the PCB become conductive becuase of the carbon. so it just keeps burning.

The only fix for that other than replace the board, is remove the inverter transformer, pay attention of the traces in the burned area. Take a dremel router bit, and route that entire section out. Mount the the transformer back, and re-make your electrical connections with wires. Fill in the hole with silicone.

 

[CelGen]

Burned up circuit is mirror identical to the one next to it. Just solder in the new coil and run a wire from one end of the SMT cap to the leg of the coil. For added protection run another lead from the other leg to R25. You really don't need to cut out the burn in this case because the PCB is only two layers and there's nothing on the other side or close enough to be affected.

 

[techknight]

just depends on the setup. as long as its not multilayer and there is no other copper in the effected area, your fine.

In my case though, i had mains run through a burned area on a board I once worked on. So i had to redo it all.

 

[Bunsen]

Sounds like the perfect time to replace the compact fluorescents with LED strips.

 

[beachycove]

...replace the compact fluorescents with LED strips.

Can that be done?!

 

[techknight]

yes. ive done it on multiple occasions.

I modified a 32" Sharp TV from CCFL to LED. took some hacking in the power supply circuit so the main CPU wouldnt shutdown due to inverter malfunction.

 

[CelGen]

Sounds like the perfect time to replace the compact fluorescents with LED strips.

I'm interested. I know where I can locally buy rigid and ribbon based strips.

Thing is the power light will blink because it thinks the inverter is FUBAR.

 

[techknight]

Thats when you trace the error signal and pin it to the proper logic state.

Most error return signals are active-high, so you hold it low. When it goes high, it signals the CPU to error out.

Umm, not sure if its labeled or not, but you may be able to find a datasheet to the IC that runs the inverter. Then from there, you could follow the error return signal. Thats what I normally do if the plug pins arent labeled what they are. Most modern inverters have 3 signals: Enable, PWM, Error