LG W2252TQ-PF, high-pitch noise remaining after repair

[TKMANKINDV2]

Hello everyone,

So... First, I am not an electronic enthusiast, I had few lessons in school several years ago but nothing really technical. No surprise if what I ask in this topic can be easy stuff for you

My previous monitor (LG W2252TQ-PF, an 21" LCD monitor without LEDs @ 1600*1050 / 16/10) died one year and half ago. Before dying and for a good week, he produced an high-pitch noise at specific situations (in sleep mode, even offline but power connected, and between resolution changes) and so I expected it to stop working, and he did. Unable to start it again, I stocked it somewhere and replaced it by a new one.

I wanted to repair it someday mostly by curiosity, and yesterday I finally got time and motivation to repair this old guy. I opened it, saw two bad capacitors but decided to replace nearly all of them (8, all Su'scon). Of course, I respected polarity/capacity, security and bought some decent replacements (Panasonic for the most part). The only ones I didn't replace was the two 68µf @ 450v but they didn't look bad.

And he works again ! The image is fine in all areas, I don't see any problems BUT... he still produces the high-pitch noise he did before dying, in the same situations than before. Obviously, this sound is not coming from the capacitors or maybe from the 68µf ones I didn't replace ?

I can't pinpoint the exact location of the sound, the only thing I am sure is that it come from the power board, but as I don't want to get an accidental hurtful discharge, I prefer to avoid getting too close of it while it is working, now that he got some power in nearly two years

So I want to know your opinion of it, or if there is a way to know what can produce this damn sound offline.

(I attached an image of the power board. It is not my image, I found it in the web but it is exactly the same board. If needed, I can produce some...)

Cordialy,

[stj]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

did you check the soldering for cracks on large items - specially the transformers?

[TKMANKINDV2]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

No, I didn't. I only took care of the capacitors.

I will check and redo any suspicious soldering I will find when I have the time Until then, the monitor is unplugged.

[SteveNielsen]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

You can use a flexible plastic tube (like for a fish tank air pump) with one end to your ear (don't stick it in too far, just enough to hear through the tube) and the other to move around the area of the noise to help narrow it down to a specific part. Most likely a transformer or coil.

[TKMANKINDV2]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

Hi,

SteveNielsen, I just tried your idea but I guess that I didn't have a good plastic tube... I think that 1/3 of the board, at the bottom-right of the previous image, has the highest volume with maybe a preference for the coil, but I can't confirm as the tool wasn't great.

Just to be sure, I want to ask two informations from everyone :
- In the first image I attach in this post, I guess that the curiously shaped soldering (not conique) must be replaced ? I can see this shape in multiple location, it will be a lot of work...

- I think that the green (and solid) goo at D102 and D104 is some kind of glue in the second image, but can someone confirm ?

[stj]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

the star shape on the soldering is fine - it's a rivet under the solder to make the board stronger.

the green is threadlock used to stop the ferite beads vibrating

[TKMANKINDV2]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

Hello again,

I tried redo some of the soldering, and I even replaced the two 450v 68uF as the sound seemed come from there, but the high-pitch noise is still here.

That means that it is probably the transformer at location T101, the yellow-plastic cube at the middle-right of the first image. It is written AT0471 / LC SA01 L / TF-2820-W52.

Unfortunately, I failed to find a location to buy a new one... Some people said that some glue can fix this problem, but I don't see where I should apply it (is this the datasheet ? it is visually similar and it is written TF-2820, but mine is partially enclosed). Build a brand new one is probably possible but not for me, I don't have the tools nor the time and competences.

I guess that my best course of action is probably to buy an old powerboard on eBay from China, at least if I want to remain costly-efficient, or just don't care and unplug the cable when not needed. But for this last option, I want to know if this sound is just a sound or if it means serious problems at long term.

[TKMANKINDV2]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

Hello again,

So... I let this thing "sleep" somewhere for a year and I just retried recently. Yes, I am somewhat stubborn

I think I know what is generating this high-pitch noise : the blue cap at location C102 (cf screenshot). It is a 2200 pf 1kV capacitor. It is in the area where the sound come from and each time I touch it with a screwdriver (with caution), the sound change a bit. It is the only one who do that.

As it is a high voltage stuff, I don't have any way to take some measurements, and I am not motivated to do that anyway, too dangerous.

I tried to replace it by a new one after waiting some days that the board discharge itself... but the new one generate the sound too.

So I am stuck. I wonder if I just have to sink it into some silicon, or maybe an other way ?

[CapLeaker]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

replace it with a better one? are you sure that the noise is coming from that HV cap?

[stj]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

i have heard of ceramics making noise - they can act like a piezo transducer.
what is more interesting, is why changing it didnt fix it and it never happened originally.

i wonder what it does, and if something has shifted its operating frequency?

[TKMANKINDV2]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

Hello,

Sorry for the VERY LATE response, computer crashed, bookmarks lost, etc. and life Now I am determined to finish it because if I failed, it goes into the recycle bin in a month at maximum. I need a second monitor asap as the one I had is dead.

So, hum...

replace it with a better one? are you sure that the noise is coming from that HV cap?

I can't be sure at 100%, but I tried to touch the resistances and capacitors near C102 with the screwdriver (with the same ulmost care) but only the HV C102 cap does a reaction : the sound changes a bit, as long as I am touching it. I haven't try to test the transformer, as I don't know if I would get an electrical welcome. Better safe than sorry.

I can certainly replace it with a better one, I will buy some on the web. Just to be sure, I need to find higher voltage, but stay with same capacitance, right ?

i have heard of ceramics making noise - they can act like a piezo transducer.
what is more interesting, is why changing it didnt fix it and it never happened originally.

i wonder what it does, and if something has shifted its operating frequency?

It happened originally with the old cap, it was the reason I soldered a new one. I didn't expect that it would act the same, this is baffling me too.

[TKMANKINDV2]

Re: LG W2252TQ-PF, high-pitch noise remaining after repair

Hello again,

I just changed the C102 blue cap with an another one, same capacitance but 3 KV.

There is no high-pitch noise while off anymore, this is a progress.

But, there is one similar noise while on, a very feint one. Apparently this sound disappear when the resolution is changing, and return once it has something to display.

It is not a trouble as it is not like the previous sound who was very loud, and even with new caps the rest of the monitor is still old so I guess it is normal.

Still, I only tested for 2 hours so far. No problem for the moment but I will try it with serious stuff to display once my real computer is back online (PSU gone, 7 years warranty, dead after 8 years ).