Dell Inspiron N5110 Fluctuating Voltages

[JJR]

I have here a Dell N5110 that will not power with or without the battery.
After dismantling I found the CRT board showing 19v when disconnected from the MB but when connected it fluctuates between 1.2v and 3.6v

When disconnected from the MB PU3801 gives 19v on pins 1,2,3,5,6,7,8 and 3.2v on pin 4
When connected it gives 1v to 3v on pins 1,2 & 3, 0v to 0.38v on pin 4 and 0v to 1.5v on 6,7,8

Any help would be appreciated

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

I also checked PU4002 & PU4003

PU4002
1- 0v to 0.38v
2- 0v to 0.38v
3- 0v to 0.38v
4- 0v
5- 0v to 1.6v
6- 0v to 1.6v
7- 0v to 1.6v
8- 0v to 1.6v

PU4003
1- 0v to 0.38v
2- 0v to 0.38v
3- 0v to 0.38v
4- 0v to 1.6v
5- 0v
6- 0.38v
7- 0.38v
8- 0.38v

[caspian]

Re: Dell Inspiron N5110 Fluctuating Voltages

measure resistance on all pins of PU4002 and PU4003.

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

Thanks for your reply Caspian, is that resistance from pin to ground?

[caspian]

Re: Dell Inspiron N5110 Fluctuating Voltages

yes, resistance to ground is important on these two transistors.

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

I wont be able to get back to this until Monday, thanks for you assistance so far.

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

OK, back to work

Resistance to ground

PU4002
1- 44 ohms
2- 44 ohms
3- 44 ohms
4- 101k ohms
5- 201k ohms
6- 201k ohms
7- 201k ohms
8- 201k ohms

PU4003
1- 43 ohms
2- 43 ohms
3- 43 ohms
4- 201k ohms
5- 13M ohms
6- 13M ohms
7- 13M ohms
8- 13M ohms
pins 5-8 steadily drop to 4.5M ohms

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

PU3801 on CRT Board

1- 286K ohms
2- 286k ohms
3- 286k ohms
4- 47k ohms
5- 35M ohms
6- 35M ohms
7- 35M ohms
8- 35M ohms

[caspian]

Re: Dell Inspiron N5110 Fluctuating Voltages

Now you should check all the components located between PU4002 and PU4003 to discover which one is shorted.

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

Thanks Caspian, this takes me a long time as I don't really know what I'm doing and I don't want to fry anything while I am learning.
Do those reading indicate a short to you? I am assuming 100K ohms and above is open circuit.

[caspian]

Re: Dell Inspiron N5110 Fluctuating Voltages

A resistance between 100K ohms and 30 Mega Ohms indicates a very good condition in that part of the mainboard. But the resistance of 43 ohms seems too low. Do you know how to inject voltage to find a short?

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

I bought a bench psu (30v 5a linear) at the weekend, but a bit scared of frying the board

[Techtiger]

Re: Dell Inspiron N5110 Fluctuating Voltages

Caspian you have indicated 43ohms or less seems a short doe’s this apply to every part of the Motherboard ?

[mosfett]

Re: Dell Inspiron N5110 Fluctuating Voltages

Motherboard work in power?

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

What concerns me is what to apply voltage to.

[caspian]

Re: Dell Inspiron N5110 Fluctuating Voltages

Caspian you have indicated 43ohms or less seems a short doe's this apply to every part of the Motherboard ?

no, it was for this section of the mainboard.

[Techtiger]

Re: Dell Inspiron N5110 Fluctuating Voltages

Ok thanks

[JJR]

Re: Dell Inspiron N5110 Fluctuating Voltages

Unfortunately I had to give up on this board, a used board was found at a very good price so everyone is happy. Except me LOL!
Thanks again for trying Caspian.
Dave