What can I do here please fellas? - Page 1
Forum section: electronics / projects

author: orbiter
author_rank: Frequent Contributor
timestamp: October 14, 2011, 07:40:59 pm
content: Hi All,I'm in the process of replacing the power supply socket on a Asus eee pc 904HD netbook, which is ordinarily quite a straight forward thing to do. However this netbook came to me looking like it had been dropped on it's side, the power socket was stuffed right back into it's hole and the socket itself broken. Not only that but a tiny SMD resistor behind the socket had been ripped off it's joints too.Luckily I found the resistor rattling around inside the netbook (pictured) but this is where I'm stuck, as I don't know what the resistor is as I've no idea what value it is, and I can't test it as it's damaged and has no ends. There are similar looking resistors on the motherboard but they're all different values.I've had a go at trying to solder the resistor back on but it's futile without it's factory soldered ends. I've also had a google for a schematic on this netbook but I'm not having much luckAny advise on what I could try here please guys?The resistor goes here, right behind the power jack socket.The tiny SMD resistor on the right is the one I can't value or refit.Thanksorb

author: Rufus
author_rank: Super Contributor
timestamp: October 14, 2011, 08:14:18 pm
content: It doesn't look like a resistor.Looks like it is straight across the DC input so not much point having a resistor there.Could be a varistor.You could try applying some voltage through a current limiting resistor and see if you can get what is left of it to draw some current. I would guess at around the dc supply voltage + 50%.

author: jimmc
author_rank: Frequent Contributor
timestamp: October 14, 2011, 08:48:13 pm
content: I agree it's not a resistor but I think it is much too small to be effective if a varistor at these power levels.I suspect it is a ceramic capacitor used to decouple the DC input. (There are four other (brown) caps visible in the picture.)You could probably run without the cap fitted but radiated interference would be higher.If I had to guess I'd fit something like 100n 50v in an X7R or Y5V dielectric (avoid Z5U)Jim

author: orbiter
author_rank: Frequent Contributor
timestamp: October 14, 2011, 09:16:09 pm
content: Ah ok.. Thanks a lot for help and advice guys. The board input at the socket is 14v if that helps any.When trying another cap is it crucial to use an SMD one, or can I use a small 100nF through hole? I have a good bit of room in that area so I could make one fit.Here's a couple more images of the other similar components.Thanks again guysorb

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 15, 2011, 01:49:38 am
content: if its decoupling caps, then you can replace it with through hole, no problem. and as jimmyc said, you can even live without having any.

author: orbiter
author_rank: Frequent Contributor
timestamp: October 15, 2011, 09:44:24 am
content: OK Brilliant,New power socket parts are coming Monday, so I'll give it a go then.Thanks very much for the help guys.orb

author: Rufus
author_rank: Super Contributor
timestamp: October 15, 2011, 03:01:00 pm
content: I don't see why it is going to be a capacitor there unless it is part of a filter with some inductor on the other side of the board.Switch mode power bricks are leaky. With a meter I measure 80v AC to ground on the output of my notebook supply.When you plug in the power jack if the hot side connects first you can put a 100v spike on the +ve supply input with respect to ground and if the netbook doesn't have a ground connection through some connected peripheral it is still grounded to some extent through stray capacitance.A varistor would clamp that spike and couple it to ground and there isn't enough energy to need a big varistor.I don't know that a varistor is needed. There is probably a lot of capacitance to ground on the +ve supply which you would think would soak up the spike anyway, but, if there is a lot of capacitance to ground what is a pissy little capacitor next to the power jack going to do?I would still try to put some voltage across what is left of the part through a limiting resistor (1k or so) and see if you can get it to draw any current.

author: orbiter
author_rank: Frequent Contributor
timestamp: October 15, 2011, 05:33:02 pm
content: Quote from: Rufus on October 15, 2011, 03:01:00 pmOK I'll give that a go later this evening Rufus. Dunno how I'm going to go about connecting anything to that part yet thoughorb