Kogi L7EH monitor

First thing I'd check are electrolytic capacitors, they're the most common thing I see fail in any switchmode power supply.

Inverter and CFLs. I could see absence of a good signal or the presence of a fault signal from these inhibiting the psu.

flashes,

Further information:

I was able to test the PSU at slightly above the nominal 4 amp rated capacity, and it did fine. Voltage dropped a little, to 11.5V, but the green LED stayed solid.

I was finally able to get the monitor apart, and disconnected and removed the main circuit board into which the PSU plugs. Then I plugged the PSU into that board, and got the same problem as before - no voltage and a blinking PSU LED. So it seems something is shorted in the circuit board - which at this point is no longer even connected to the LCD. But, when I measure resistance across the power input of that board, there doesn't appear to be a short. Lots of capacitance, but no short.

So then I removed the electrolytics that appeared to be part of the power input section, and tested them as best I could, but they seemed fine.

What's left is a switching regulator marked 8050SD, and a surface mount Schottky diode marked SM340A which is part of the output circuit of the regulator. And it seems to me that one or both of these has to be the problem. It doesn't seem likely that a short further into the circuit would feed back all the way to the power supply input if the regulator was ok. Of course such a short could have destroyed the regulator, so just replacing the regulator might not be the solution.

Well at this point I may just go ahead and order those parts if I can find them, and see if that will do it. As a practical matter, the electrolytics seem fine, and there's nothing else on this SMD board that I would be able to replace anyway.

How did you test the lytics? You need an ESR meter to get any meaningful results.

Were the CCFL drivers disconnected? If not I'd suspect them first.

You really need an ESR meter to accurately test electrolytics especially when they are in circuits where high frequency signals are involved. Is the inverter located on the main board? There is a remote chance that the LCD/CFLs/Inverter needs to be in circuit to render a 'good' signal to the PSU. I've not done too many stand alone monitors (2) but have done a good dozen laptop displays.

Please update us if you find the culprit(s) as I and probably others archive this stuff for future reference.

Yeah, but I don't have one of those. I just figured if they appeared to behave normally when tested with an analog ohmmeter, they probably weren't the cause of what appears to function as a near-dead short.

I don't know. The logic output lines to the LCD come from this board, and they were disconnected. The backlight supply, however, appears to come from another board, but that was also disconnected from the board I tested.

And, there is no "good" signal to the power supply. The power supply is just a 2-connector 12V brick that plugs into the monitor. It operates fine on pure resistive test loads from infinity down to 3 ohms, but goes into shutdown when plugged into the monitor. And this is without even pushing the Power button on the monitor, so whatever is wrong is apparently drawing excess current even in vampire mode. That's what made me think it must be something fairly early on in the monitor's power section.

Well, in any event, the owner has decided not to invest any money on it given its age, so I'm not going any further with it. Of course I'm curious about what's wrong, but I'm not going to fund the research. That particularly doesn't make sense given the limits of my knowledge and the fact that almost everything is surface-mount (i.e. - unrepairable by me even if identified as the culprit).

But I very much appreciate everyone's comments and suggestions.