OpenWrt Forum Archive

Topic: WRT54G v2.2: replacement of some damaged SMD components

The content of this topic has been archived on 5 May 2018. There are no obvious gaps in this topic, but there may still be some posts missing at the end.

Hello,

A few months ago, I hurt my WRT board a little while opening it, partially ripping off a capacitor and a 5 leads component. Then stupidly tried to fix it with a cheap 25W soldering iron and its burned tip. Oh, and a little glue to keep them in place firmly... roll
That was my first time at SMD rework and it didn't left me with a good impression.

As you can (or cannot) see on the (blurry) photo below, the result was not as expected. Since then, no radio interface showed up and I was left with an expensive wired router.

Now that I own a hot air rework station and all, I'd like to train my skills.
It seems to me that the battlefield I wasted is the alimentation of the radio part of the router, located just under the Faraday shield.

Could someone which has already tinkered his/her way in a similar version of the board put a name on the U8 chip, please? The part is burned and inscription are unreadable here.
Last but not least, capacitors C82 and mostly C106 may have been damaged, do you know roughly their values?

Thanks in advance for your help.

http://i.imgur.com/sE1pO.jpg

Hey, if you post clearer images I can try to see what are those components..btw the capacitor seems a 1uF-10uF 16V ceramic, not trivial. The other can be a LDO (Low Drop-Out voltage regulator)

Thanks for your help dabyd64!
I'll try to put a better photo online. Since capacitors don't have any markings and the one from LDO have been erased with my soldering iron, I thought this wasn't useful.

Since then I've been able to identify the 5-lead chip, a LDO as you assumed.
A friend of mine has a v2.0 board with a pretty similar design to my v2.2: same components at the same location. The marking on the 5-lead being 'LAYA'.
I found its reference (LP2985AIM5-1.8) on an older version of the datasheet (p.3): http://www.ti.com/lit/ds/snos510o/snos510o.pdf
It's the SOT-23 package, 1.8V A-grade version of the component.
They come really cheap at Farnell (a few cents in France): http://fr.farnell.com/national-semicond … dp/1469131

If needed, I will scavenge the C106 cap on a useless v6.0 board which has a quite similar radio alimentation circuit (different LDO though).

I'll keep you updated.

Nice ! Sometimes is really hard to find the component with the smd marking code. You had luck! If they're chinese copies then it is almost imposible.
For the smd capacitors, solder some capacitors as big as possible, that could fit in that size, but cheap.
I recommend you some 0805 size, 10uF capacitor, since a bigger value is better for the voltage stability, specially in RF devices.
Most of the smd ceramic capacitors used in boards are 100nF (0.1 uF) for decoupling. Only a few are more than 1uF.
Usually, the color will give you a hint. The more brown it is, the more capacity it will have, but not always. Source: My electronics experience.

Just in the case you wanna buy them I found those in ebay for less than $3 (50pcs):
http://www.ebay.com/itm/50-PCS-0805-10u … 3373aa8757

Let's hope you will fix that!

If you for some reason still need pictures of the WRT54G v2.2 board - let me know as I have one here somewhere.
(virgin board, everything untouched so far)
Wife has a good Nikon so it should be doable.

/Huldu

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