WRT54G Power Supply Chip

[ParkingLotLust]

If you search my recent posts, youll see I have a buzzing WRT54G. The power brick is whats doing the buzzing. I discovered that if I removed the PWM chip, it stopped. I purchased a replacement and installed it, and now it still buzzes. This leads me to believe the other chip might have been bad. Since I have no freakin' clue whats wrong with it, Im left replacing chips until it works again. Anyways, I need an equivalent to a chip with the following markings. I google'd it and couldnt find any matches in terms of the markings.

9936
:delta:31B9M

It is an 8-pin SOIC chip, located right at the power input. I can try and get a close-up picture of the location of the chip if it will help.

 

[justDIY]

the wrt54g contains an onboard buck converter, I believe accepting up to 20v and down to 5v, the unit itself running on 3.3v.

have you tried using other power bricks, to see if they have the same problem?

my wrt54g (all three of them) came with heavy unregulated "12vdc" power supplies ... the heft implying a simple transformer + rectifier + cap configuration, leaving the regulation to the chip onboard the wrt

in the field I run my wrt off a parallel bank of 6v gel-cells which fit nicely in a small camera bag, but have also run it straight off "12 volt" power from my truck and a 12v deep-cycle battery, it's a pretty flexible chip

all that being said, if there were something wrong with the chip, it would either not work at all, get terribly hot, smoke something else in the router or all of the above. has any of these symptoms occurred?

 

[ParkingLotLust]

I replaced the synchronous buck pwm controller chip. That was my first guess since it would handle the incoming power, but that didnt fix it. I bought it for $20 off eBay, as being broken, as something to play around with.

Its running off the power brick that came with it. I have a v5 running dd-wrt but theyre a different voltage brick, so I dont want to hurt it. I believe the one I have is a v1 or a v2 (with the mini-pci card on the wrt54g board). Anything else I can try before I start replacing more chips?

 

[mvs sarma]

Hi,

whether the buzz (if it is audible) is not due to transformer packing being loose and the coil former sitting loose on the Ferrite core and things like this--

 

[ParkingLotLust]

So what should I do to fix it? I dont quite understand what you're saying.

 

[Oznog]

Also a bad output or input cap can cause instability that can make audible buzzing.

If the supply has a prob causing terrible ripple, that can cause a similar instability prob.

 

[ParkingLotLust]

So try replacing the big electrolytics by the input jack aswell? Ill try another power brick too if I can get my hands on one of the same rating

 

[Nigel Goodwin]

To be honest, I would have thought the least likely cause is going to be a faulty IC - as suggested FAR more likely is the transformer mechanically noisey, or a faulty capacitor.

 

[ParkingLotLust]

Will it do any damage to remove a capacitor and test?

 

[Nigel Goodwin]

Will it do any damage to remove a capacitor and test?

Presumably you mean test the PSU without the capacitor fitted?, depending on the capacitor it might well do LOT'S of damage.

 

[ParkingLotLust]

Hmm which caps are we talking about, that could be bad? the ones in the power brick, or the ones on the board of the router?

 

[justDIY]

whichever electrolytics there are, replace 'em both, they're cheap!

I see two on my wrt54g rev 1

 

[ParkingLotLust]

My board looks more like this. Which caps should I be replacing? The big pair, or the small pair?

**broken link removed**

 

[justDIY]

oh, that's not your board ... but if yours look like that, with no visual signs of distress, I'd be highly suspect of anything being wrong with the caps.

if you still want to replace any, replace all four, two big ones and two little ones.

 

[ParkingLotLust]

Thats exactly what my board looks like. No visual signs of wear or anything. Thats why I suspected the chip, because when I removed it the buzzing stopped, but it obviously still doesnt work.

 

[Nigel Goodwin]

Thats exactly what my board looks like. No visual signs of wear or anything. Thats why I suspected the chip, because when I removed it the buzzing stopped, but it obviously still doesnt work.

If you unplug it from the mains the buzzing will stop as well, it doesn't really help much.

Presumably then, you've not made it clear before, it's buzzing but not working?.

I would check for shorts on the outputs, rectifiers S/C, perhaps a crowbar zener, or even a duff output capacitor.

 

[ParkingLotLust]

But I figured if it was a bad cap or something, even removing the chip would still have the cap shorting out, etc, causing it to put a huge load on the power pack and make it buzz. Correct, its buzzing, but nothing lights up.

How would I go about checking things? Just probe around with a multimeter? I have no clue even where to begin.

 

[Nigel Goodwin]

But I figured if it was a bad cap or something, even removing the chip would still have the cap shorting out, etc, causing it to put a huge load on the power pack and make it buzz. Correct, its buzzing, but nothing lights up.

If you remove the chip the PSU doesn't work any more - so it can't buzz.

How would I go about checking things? Just probe around with a multimeter? I have no clue even where to begin.

You should be able to easily identify the output from the transformer, through a rectifier, with a capacitor or two to ground - check on ohms across the diode and capacitors.

 

[mvs sarma]

Hi,

Do you suspect any bulge on top od caps? If not, try to replace the power brick , if you have a suitable one -- i am suspecting high ripple from that

 

[ParkingLotLust]

You should be able to easily identify the output from the transformer, through a rectifier, with a capacitor or two to ground - check on ohms across the diode and capacitors.

For the xformer and rectifier, you mean crack open the power brick and check, right? There is no xformer or rectifier on the board itself. As for testing caps. What should I be looking for when I first apply the leads? After ten seconds?

try to replace the power brick , if you have a suitable one and try-- i am suspecting high ripple from that

As soon as I find a suitable one, that is my next goal.


Sorry for being a bother and asking dumb questions, but Ive gotta learn somewhere