Blown XPS 1340 inverters!

I am at a total loss, and don't know what to do.

I have changed three (read: THREE) inverters consecutively on an XPS 1340 and all I got is a dark screen and blown inveters. Did check that I have an LCD screen - LED screens do not require an inverter strip, CCFL-powered screens do.

Am I doing anything wrong? I have searched for the exact part number and lot number both on Amazon and Google, but every purchase ended in vain - a fizzle in the screen every time I press the power button! So I ended up with three junk inverters on my work table right now.

If you need the part numbers that I have, here they are:

One of them did work fine for a week (207S00391AA) and started to flicker, and decided to blow itself and burn the PCB on it.

Any thoughts? Shoot me up questions and I'll be happy to answer it.

 

I don't understand why you bought all these funny-numbered inverters instead of just looking for an inverter with the Dell P/N P927C? Am I missing something?

 

Those were the individual lot numbers. The XPS 1340 in my possession uses P/N 0P927C.

 

So you replaced them with other P927Cs? And they still broke again?

 

Oh yes I did.

And now I don't know what to do. Could be the motherboard, CCFL (unlikely, it worked couple weeks ago), or something else.

 

I wouldn't rule out the CCFL being the culprit, but you could have a short elsewhere. If it's the CCFL, high inrush current could be responsible due to an intermittent failure somewhere. I'd check for contact points between PCBs and metal chassis components, just in case. Aside from that, look for failed capacitors (which can short), or damaged ICs. I don't remember offhand what one of these assemblies looks like. Can you either describe or take a picture of what the inverter board connects to?

 

I checked the continuity on the LCD ribbon cable pinouts and they seem to be okay. There's a bit of gray-ish image in the screen when booting, so a failed cable/LCD display logic board would be ruled out. There seems to be nothing wrong with the LCD assembly, so I'm completely stumped T_T

 

I think the reason you are stumped is that you are too focused on ruling out potential candidates, and not focused enough on what would be consistent with this sort of failure. With that many boards having failed, and given the failure mode, it sounds like the problem most likely has to do with instantaneous load at power-on. The CCFL is a good candidate for this type of failure. I don't know what else is in series with the inverter, but I'd check (and possibly replace) those components as well, if you are trying to avoid replacing the panel (or the backlight, if that's separable).

 

So, you're saying that the CCFL board may be drawing too much power from the inverter? Anyways, I noticed that when I pressed the power button prior to inverter failure, the LCD would light up for a second and then the whole computer would shutdown (I would hear the fans spin down). Odd enough for an inverter replacement.

Speaking of decapping/SMD desoldering - that would be out of the question for now, as I do not have a soldering iron suitable enough for SMD rework. My main competency lies in through-hole, but a total noob at SMD's (sigh).

I'll post more details - stay watched.

 

I don't have one of these computers, so I don't know what the inverter is connected to. Whatever is drawing power from it may be putting an excessive instantaneous load on it when you turn the power on. Your description about the manner in which it fails sounds fairly consistent with this type of failure mode.

 

It's Y-shaped ribbon cable. The long end connects to the motherboard, then branches out to one for the inverter to power the CCFL, and one to the back of the LCD monitor for video.

ADDENDUM

I checked the power supply, and it was getting 19vdc out as according to its specifications. Ran some tests with a spare known-working LCD, and still no backlight. That leaves me with the possibility of the motherboard getting too much power out to the inverter.

 

Ran tests with a known-working panel...with one of the fried inverters?

 

No, no, no. Fourth inverter (yipes!) just arrived, and it is still doing the same thing. Press the power button - a half-second flash, then a slight crackling noise and the computer turns off after that. Press the power button again, everything starts fine except for the screen.

That leaves me needing a fifth inverter now T_T

It leaves me with the possibility of replacing the motherboard, too. Before I do that, I'm gonna need some second opinions, just to make sure.

 

You aren't being clear enough for me to help you. When it failed, were you using the fourth inverter with the "known-working LCD"?