Nigel Goodwin

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.

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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

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

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.

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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

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ParkingLotLust

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?

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

mvs sarma

Ok, can you parallel an extra elecrtolytic across the imput power (say 470uF )

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Sarma.

ParkingLotLust

Pardon? I dont understand what youre saying, or more off, what thats going to do.

EDIT do you mean just connect a 470uF cap across the + and - leads coming into the board? What will that do? Im guessing filter the power? But wouldnt buzzing be more than just a dirty power supply, considering the buzzing is coming from inside the power supply?

mvs sarma

power brick but istead of breaking, i am trying to see whether buzzing will comedown-- if it reduces, then we may suspect the power brick. we need not spoil our asset(power brick by breaking) you can also supply external DC of suitable votage from any adjustable PSU if you have one -- this will help eliminate the possibilities, you see

Sorry-- it may be mid night for you-- better tomorrow morning .

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Sarma.

ParkingLotLust

I tried it with a computer PSU, and while it didnt buzz, the router still didnt work. I noticed something though, as marked in the picture (pink to make stuff show up). The yellow part is labelled:
P30V
JF34

and on the other side:

P30V
IGOU or I6OU

Voltages while hooked up to the computer psu (hooked up to 5v line):

The other side shows 0v (in reference to ground) with or without the part (obviously without)

mvs sarma

Hi, perhaps the yellow part may be a polyfuse (i mean self re-setting type)

what is the input power supply to the equipment(eqpt) ?

now you try to see the output voltages from the regulator IC. generally it may be 5V or 3.3V in modern epqt. if this is complied we ahve to see for other failures,if any.

check for too hot chips( unusual) better if you have a another piece for comparison. then check for failure of any line protection devices like transzorbs. generally these will be either two or three terminal devices. if they become short the unit under querry maynot function for that port and if in the common input entire eqpt may suffer

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Sarma.

ParkingLotLust

The input from the original power supply is 5v, so Im using a computer power supply, and connecting the router to the 5v rail. The bottom side of the yellow part is always 0v, even right at startup, i dont notice a difference. So if it is a polyfuse, could it be possible that something is blown and is shorting it out? Ive checked over the board with a magnifying glass, and there arent any shorts or torn traces.

mvs sarma

Hi, it appears, the power converter may be in the bottom plane and may be 5pin type very near to L3 torroid.

or is it one of the 8pin dip ICs?

whether the output is ok at saay 3.3V or so?

FUSE F1 APPEARS GONE????

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Sarma.

mvs sarma

Hi,

REMOVE AN CHECK F1--- suspect it is gone

also check DS1,ck1, CA3 and C3 for short-- whether any of them is warm or HOT??

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Sarma.

Oznog

I see no Full Wave Bridge Rectifier is apparent.
So the supply takes in DC from the "wall wart" transformer.

It is possible that the wall wart has either a bad filter cap or even a bad rectifier diode.

Basically I'd rate liklihood:
1. The big caps on the board
2. The little caps on the board
3. The cap in the wall wart
4. The rectifier in the wall wart.

You need some way to measure things. An oscilloscope would be ideal. You can measure the wall wart's DC output when the router is powered up but disassembled. You can try to measure the ripple with the AC scale on the meter but it may be very unreliable due to it being a higher freq than the meter was intended for. It'll probably read lower ripple than the actual value.

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I thought what I'd do was I'd pretend I was one of those deaf-mutes.

ParkingLotLust

Ill check F1. No components are getting warm/hot. The power converter is a PWM chip, the small one in the bottom of the picture. It has been replaced with an equivalent chip. The one below it is the one I described on page 1, but I dont know what type it is and couldnt find any info on Google.

As for the wall wart, oznog, it would buzz when connected, so Im using a computer power supply instead. As you can see from the picture, with the yellow thingy soldered in, the voltage of the 5v rail drops to 4.6v. With it removed, it goes back up to 5v, but breaks the circuit which would bring power to the board.