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Oh snap....I dun goofed

post #1 of 10
9/12/10 at 11:56am
Thread Starter 
Okay, so accidentaly I switched the plus and minus wire on the power adapter for my Dell Inspiron 9400.

Meaning I put +20V on the ground wire, and +0V on the live wire. (Normally it's the other way around)

After this the PC won't start at all.There is no reaction when I press the powerbutton. Are there any fuses or something on the mainboard that could have hopefully took off for my stupid mistake? Or is the entire mainboard fuked?

Thanks.
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post #2 of 10
9/12/10 at 4:08pm
there are thermal fuses on the board.

Have you tried on battery only ?

You will have to try to find a schematic for the motherboard, but yuo can always try to race the power from the jack and see if yoiu can find the dead fuse,

These fuses are typically SMT type devices, and can be very hard to repalce.


but it may well be toasted as well
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post #3 of 10
9/13/10 at 4:39pm
Thread Starter 
Unfortunately the battery is empty and there is no way of recharging it seing as the entire laptop is "dead" including the battery circuit.

If there are fuses, would those be soldered onto the mainboard and not removable by hand?
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post #4 of 10
9/13/10 at 7:41pm
Now is too late for me but tomorrow (around 7 hours from now) I take a closer look on one 9400 mainboard to see what could happened.
Power adapter is still ok?
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post #5 of 10
9/13/10 at 8:09pm
Thread Starter 
That would be nice if you could.

Yes the power adapter is still okay. I used a 130W Clevo power adapter. What's a bit weird about this adapter is that if it short circuits it keeps delivering max wattage without turning off. My fear is that the i9400 has a kind of diode reverse polarity protection which short circuits the power adapters upon connecting with the wrong polarities. This would normally turn a power adapter off, but since my adapter is a bit weird I fear it may have caused serious damage by burning out the diode, then allowing current to flow further into the mainboard.

But I didn't smell any burning or anything, so I'm just hoping there's no diodes involved. Although I seem to remember reading somewhere that most laptops use this diode system for reverse polarity protection.
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post #6 of 10
9/14/10 at 5:08am
Here is




At first sight there is no diode for reversed polarity protection.
In some cases there is no need for such diode.
At a first look (since I don't have schematic for this model) seems like first two transistors in + path could act like an electronic fuse but even if normaly applying reversed polarity will lead to block voltage at first stage damage could happen.But this could be wrong presumption.
Anyway looking at other Dell schematic voltage must be blocked at first transistor in case of reversed.

First check that coil if is ok,next take a look and check if transistors are ok. But for this you need some knowledge of electronics.

Was your 9400 charging with that charger? since you need third wire for laptop to recognize charger.

If this will help you here is a Dell charging part schematic.Looks very similar.
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post #7 of 10
9/14/10 at 12:02pm
Thread Starter 
Hi and thanks for the pictures & explanation, much appreaciated

So there is one transistor and one coil in the path directly after the powerjack? And the reverse polarity has to have been blocked by the first transistor. Do I understand this correctly?

If so, I have a multimetre lying around. Would that be suffient for testing the two devices?

I could also try and plug in the poweradapter, then check various components for where there is a voltage drop. If there is zero volts behind the coils/transistor, I would know for sure those are the culprits, correct?
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post #8 of 10
9/14/10 at 1:33pm
Some like that.
Set your multimeter on continuity test (most of them have this) and without any power source connected check coil marked as PL2 you should get a sound or some indication like when you touch together both leads.
If you get higher value could be coil damaged.

Next step is to check if is not shorted to ground.Put one lead on coil terminal and one on ground (or any metallic shield on mainboard, in that case there must be some value of indication on multimeter but not like in coil case.

Beyond this you have to have much attention on what you do.Is a little risky for someone without a little practice.

Next if coil seems ok attach battery then charging plug then do few measurements.
I think best way is to keep mainboard in case with upper part removed.
Black lead put on some metallic shield of mainboard and with red lead do some checks on few components. (I'll edit my previous attached pictures in few moments to indicate where).
Depending on results can go further.
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post #9 of 10
9/15/10 at 1:12am
Thread Starter 
Alright that sounds good, thanks for the help. I will check the coil first, then proceed to check components as you marked on the drawings and report back here. Thanks again for all the explanations and help, as I would have never figured out this on my own lol
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post #10 of 10
9/15/10 at 4:21am
Good luck!
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