Netgear WNDR3700 Whining Sound

[shpitz461]

Re: Netgear WNDR3700 Whining Sound

So you're saying the caps can be bad even if they physically look OK? I'm not seeing any bloatness nor any deposits. The smell is really bad, and is very strong.

Also, it looks like I damaged a small ceramic cap near that yellow arch while trying to pry the case open.

I'm going to look in my storage bins to see if I have a similar adapter. I also saw on eBay a new adapter for $14 shipped, not sure if I want to start replacing every part while not being 100% sure the adapter is bad. I'm almost positive it is.

I'll follow Mock's and RW's ideas about measuring and report back.

Thanks guys!

[shpitz461]

Re: Netgear WNDR3700 Whining Sound

So, got a new adapter from eBay, the high-pitch sound is still there. I'm at a loss at this point.

Can other components make the sound or only the caps?

Anything I can test for (voltage/amps wise)? if so, where?

[mockingbird]

Re: Netgear WNDR3700 Whining Sound

Never plug adapters from eBay into your peripherals.

[mariushm]

Re: Netgear WNDR3700 Whining Sound

It's not the capacitors that make the whine, but most often it's the inductors, those coils of wire around a ring or a bar of ferrite/metal powder/etc.
When pulses of current go through them, the wire expands and shrinks a bit, scratching against the coils and against the ring.
When capacitors go bad, the circuit gets "out of balance" and this inductor noise can be more pronounced.

In the adapter, you have all that glue that locks the coil on that ferrite core ring, so that it won't scratch against the ring and the components around to make sound.

Inside the TV, right near those two capacitors in the green circle, you have two small inductors, one that has 150 written on it, and one saying 4R7
On the right, you have three inductors, but those are unnamed.

Anyway, if you're sure the whine comes from the green circle area, you can try to determine if the inductors make the whine by gently pressing with the finger on those inductors. This may prevent vibration a bit, just as you would put some of that white glue like substance you see in the adapter.

There's another issue that can cause the whining.. see those two small chips right at the top right in the green circle, to the right of the inductors?
Those are the switching regulators, which convert a higher voltage (let's say 12v) into the lower voltage, maybe 2.5v or 3.3v or whatever, doesn't matter now.

They're supposed to run at a specific frequency, let's say 240 kHz, which is set by some surface mount resistors and capacitors that are somewhere near those small chips.

If for some reason, one of this surface mounted capacitors or resistors cracks or goes bad (it can happen, and in some cases there's still some capacity or resistance but varies with heat), the chip will not run at that frequency of 240kHz or the frequency it was designed for but a different one which however makes the inductor whine.

It's sort of like what happened with Tacoma Narrows Bridge : http://en.wikipedia.org/wiki/Tacoma_Narrows_Bridge

The smell in the adapter can be caused by electrolyte leaking but it can also be caused by that white gunk drying out due to repeated cycles of heating and cooling
It looks quite well made otherwise, that adapter.

[redwire]

Re: Netgear WNDR3700 Whining Sound

The whining sound is due to the switching regulators going unstable when the capacitors fail. It comes mainly from the inductors and some from the ceramic caps.
If the capacitors in the AC adapter or the router's main board go bad, you can get a hissing or whistling sound.

At this point (after your recap and new AC adapter), I think the new caps you put in (Lelon) are el-crapola, or the router is overloading its voltage regulators. Sometimes the AC adapter's capacitors die which then takes out one of the main board's cap, due to the high ripple currents. They can look fine but will run hot.
Otherwise, measure the voltages on the 4 caps and see if they match my earlier post.

[ratdude747]

Re: Netgear WNDR3700 Whining Sound

Never plug adapters from eBay into your peripherals.

That should be a rule of hardware. Unless it's a genuine OEM one...

[tang3nt]

Re: Netgear WNDR3700 Whining Sound

Hi All, I know this is an old thread but it's relevant in my case since my WNDR3800 just started to whine last week with "radio death" as a bonus.

The electrolytic caps are on order and I'll be replacing them all just to be sure. Outside of that, I noticed one of the three components (2nd picture, there are two right in line below the cap by the power switch and one to the left) is kind of bulging at the top. But I don't know if this is also a capacitor of another type or another component altogether. What is it and should I replace it too?

Also, anyone know if the original poster fix their WNDR3700 and what did it?

[mockingbird]

Re: Netgear WNDR3700 Whining Sound

Are you talking about the inductors? Can you take a picture?

You might want to give some attention to the power adapter too. If the input power is not clean, you can use the best capacitors, it won't help.

[tang3nt]

Re: Netgear WNDR3700 Whining Sound

In the 1st attached picture, those in the red box, they're the inductors? The one that looks visually "off" is the one circled in yellow.

The rest of the attached pictures are close-ups.

[mockingbird]

Re: Netgear WNDR3700 Whining Sound

Yea, those are just inductors... It looks a bit funny, but it's probably just the heatshrink that was shrunk a little too much, so it's most likely fine.

[tang3nt]

Re: Netgear WNDR3700 Whining Sound

Well, I recapped the router, but it's still making the same noise. I tested the voltage on the power supply. Got a reading of 12.30V plugged into just the outlet and 12.25V after plugging into the router.

The noise on mine seems to be coming from the same place as in picture two of the original poster. The green circle.



Any thoughts or ideas on what to look for next or is this a lost cause at this point?

[mockingbird]

Re: Netgear WNDR3700 Whining Sound

You need to measure ripple in the output of the power adapter to get a good idea of how much AC noise is coupled with the DC current. To do that, you need expensive equipment.

It's a lot more economical to just re-cap the power adapter. 99% of those adapters that come with routers use substandard caps, and that may very well be the cause of the squealing.