This is stinking annoying, Whats the problem?

[formulav8]

I have a dv9500 lappy with core2 and I think nvidia 8600m graphics.

The problem is that the lcd doesn't brighten up. You turn it on, and you can see the hp logo very dimly (you have to look hard to see it). Basically the backlight isn't working.

I hook up the lappy to a monitor using the vga output and its perfectly fine on the tv monitor.

I've tried 3 different inverters, 2 different lcd screens, and 2 or 3 lcd cables.

Now heres what screwy. If I touch the inverter on a certain resistor/area the screen lights up nice and bright. As soon as I stop touching the inverter in that area it dims back down. All 3 inverters, Lcds, and cables were changed and it still will only work correctly when I press down on a certain area of the inverter.

I'm guessing i'm doing some sort of ground or something and it works. I've tried unhooking this, and that, and taking parts off the mobo, unhook uneeded mobo cables, drives, and tried to keep the lcd from grounding and so on and it still will only work when I touch the inverter.

Also while I am touching the inverter with the lcd bright, and then touch the metal on the lcd frame or other ground, the lcd dims back down.

So... Whats the problem? Anyone know how to fix this thing? I'm not sure if the nvidia gpu defect could have anything to do with it and if it needs to be reflowed (maybe just one pin isn't contacting properly on the chip for all I know). Thanks for any help.

 

[Stuka87]

You may have a bad ground, and/or ground loop.

Typically there is a mesh ground strap that goes from the LCD to the chassis. Does this machine have anything like that? It sounds as though you have voltage sag so the backlight can't fully turn on due to a bad ground.

Although touching components also adds a fair amount of capacity, although in this case I don't think thats an issue (Thats typically an RF thing).

 

[formulav8]

Hi, it doesn't appear to have anything like that. Only one cable which plugs into the wide flat retangle slot. And then the cable splits to provide a connection to the inverter and to the motherboard. Of course at the bottom of the lcd a two piece wire connector that connects to the other side of the inverter.

Two different lcd's were tested with the same results.

 

[KingFatty]

Are any of your capacitors swollen at all (e.g., look if the metal dome on the top is rounded instead of perfectly flat, or if the sides/circumference is bulging at all)?

Maybe you have a bad capacitor somewhere that you haven't replaced, and when you touch the inverter you add the capacitance needed to compensate for the bad capacitor?

Take a very close look at the capacitors:

 

[KompuKare]

Fairly sure that despite the 8600M in this case Nvidia is blameless. (Which doesn't mean the 8600M would not bumpgate sometime in the future of course.)

If you've replaced both the relevant parts, something else must be wrong. These kind of things are hard enough to diagnose in person much harder at a distance but let me try few ideas:

- With a bright torch can you see something on every part of the screen? If yes, then the GPU can be pretty much ruled out as can the signal cable.

- Grounding causing a capacity is possible, but maybe an easier explanation would be that something isn't properly grounded, or

- those resistors you are touching have a bad solder. But since swapping out the inverter didn't work, I'd say it's more likely grounding. The input into the inverter board has tons of wires and while one or more grounds may be working, maybe one input is not?

BTW, I assume you've realised this but you don't want to touch the output from that inverter: CFCLs need a high voltage afterall.

 

[formulav8]

Thanks alot for all of the info.I will check out everything mentioned, especially the capacitors. I did try a quick reflow but no go. I did notice a weird looking discolored spot at a corner of the gpu but thats all I noticed gpu related.

I never thought to try finding a bad capacitor. Although there doesn't seem to be all that many capacitors on the mobo? I wonder if a resistor would go bad like capacitors...?

Komp, You are definitely right about the complexity of figuring out a lappy problem like this, especially over the internet. I might just get a replacement mobo and try that if I can't get it working Sunday night. I already have lots of time and money in this thing. Hopefully it will be worth it in the end.... It does have decent 8600m graphics and especially a fast T7500 2.2ghz 4mb cache cpu. But if I can't fix it this weekend I wonder if I would be better off replacing the mobo or parting it out??? I already have almost $100 in it at least and a mobo is alittle more than $100 in itself....

I will check things out Sunday and see what I come up with.... Thanks for the replys!


Jason

 

[KompuKare]

See HP DV6000s are notorious for Nvidia bump defects because they run so hot. Not sure about DV9000s.

A common diagnostic was always along the lines of: 'if ext. monitor works, the GPU is okay, but in theory (never seen it but...) it's possible for only part of the chip to be not working by for example having a few pins bad (bumpgate was about the connection from the silicon to the packing after all). That's why I mentioned the bright torch: if ext monitor works and the laptop screen displays (backlight is not relevant here!) the GPU is most likely ok.

If the DV9000s are as bad as the DV6000s though any ebay mobo you find might have been reflown and those will usually fail again. Investigating grounding might be worth it but aside from getting lucky, actually tracing the grounds is beyond my skill level.

One of my most frustrating bumpgate was a 8400M on an MXM card for this 22" AiO 'desktop'. Never found a replacement and the oven trick only lasted so long, but the frustrating part was the mobo had a perfectly adequate Intel GMA4500 onboard but due to design of MXM cards it would need a pass-through-card (sort of like an old SCSI terminator maybe). Needless to say those pass-through-cards only exist in theory...