I accidentally plugged a 110v soundbar into a 220v source :(

[zippydan]

Hi.  I have a new LG SK10Y soundbar.

In my excitement to test it out I forgot to check the input requirements on the sticker.  I plugged it into 220v and, there was no spark, no strange sounds, no smoke and no smell.  I pressed the power button, and there was a confirmatory beep, but nothing else happened.

Realization quickly dawned and I switched it to a 110v source.  Same symptoms: pressing power button results in confirmatory beep, but nothing else (there should be lights and stuff).  Also, it doesn't respond to power on signal from the included remote.

So it seems that the control panel is fine with whatever voltage was getting to it, but nothing else was...

My (limited) experience in these scenarios tells me that usually it is just the power board (or the power-related part of the board) that tends to fail.  So I disassembled the unit and it does have a separate power board.  However, after inspecting the board as well as I could (which is not saying much), I didn't notice anything obviously burnt or damaged.  The board even has a fuse but I tested it for continuity and it is fine.

I'm actually more concerned by the fact that I didn't notice anything burned, that the fuse is fine, and that the power button still gives me a beep.  That makes me think that perhaps the power board itself had no problem with the 220v input, and then passed on a stepped-down voltage that was too high and then fried something farther down the chain of circuit boards (but not the control board with the power button which still beeps).  That scenario would make this repair a lot more costly and complex, I think.

After posting this I'm going to edit this from my phone to add pictures, so if you don't see any pics just hold tight for a few minutes and check again, thanks.

Edit: had some trouble getting the pictures uploaded because of the strict size requirements here, and inability to edit easily on my phone.  Two pictures now available of top and bottom of board.  More detailed pictures available upon request.

The power board seems to have a rather straightforward, simple design.  I think my first task would be to test to see if this board is outputting the expected voltages from a 110v input.  You can see the input connector with fuse on one end, several capacitors and a transformer in the middle, and then a connector cable at the opposite end which connects to the next board in the chain.

[OwO]

I'm actually more concerned by the fact that I didn't notice anything burned, that the fuse is fine, and that the power button still gives me a beep.  That makes me think that perhaps the power board itself had no problem with the 220v input, and then passed on a stepped-down voltage that was too high and then fried something farther down the chain of circuit boards (but not the control board with the power button which still beeps).  That scenario would make this repair a lot more costly and complex, I think.

That's unlikely because I'm fairly sure this uses a SMPS which regulates output. It's possible it's just defective and wouldn't have worked on 110V either.

Since there is no sign of damage I would return it for RMA 

[Mechatrommer]

what the manual says? maybe thats the way it is.

[zippydan]

I'm actually more concerned by the fact that I didn't notice anything burned, that the fuse is fine, and that the power button still gives me a beep.  That makes me think that perhaps the power board itself had no problem with the 220v input, and then passed on a stepped-down voltage that was too high and then fried something farther down the chain of circuit boards (but not the control board with the power button which still beeps).  That scenario would make this repair a lot more costly and complex, I think.

That's unlikely because I'm fairly sure this uses a SMPS which regulates output. It's possible it's just defective and wouldn't have worked on 110V either.

Since there is no sign of damage I would return it for RMA 

Argh. The problem is that it is a US model that I am using overseas (hence the difference in voltage).  I doubt I could get the local LG to honor the warranty.

I've uploaded the pics of the board now, can you take a look to confirm that it uses SMPS?  I can provide more pictures if necessary.

Thanks for your help.

Edit: Oh, heh.  I see it says SMPS right on the board itself by the model number and revision number.  So, does that mean that this board would have had no problem with a 220v input?

[Richard Crowley]

Yes, it is definitely a SMPS.  It is increasingly rare to find linear power supplies in anything these days, consumer goods, or even professional gear.  You confirm that the fuse (F901) tests good (a very few ohms of resistance). 

The mains power input appears to be across the PW901 connector.  Is FL901 good?  What is the resistance across the two spark gaps?  They should each  be very low.  And in a similar manner across FL902?  From each of the "top" pins to the corresponding "bottom" pin?  (as shown in your photos).

The output appears to be those multiple wires coming out the end of the board. If you can safely plug the board into 110V mains, what voltage (if any?) do you measure across the output (C925)?

REMEMBER THAT MAINS POWER SUPPLIES ARE DANGEROUS, LETHAL, EVEN.  And SMPS are even more dangerous than conventional linear supplies.  And they pack a lethal charge even minutes/hours after disconnecting from the power mains.  You will see responsible people like Dave and BigClive very carefully discharge (short out) that big input capacitor (100s of uF and 100s of volts) before messing with the SMPS board.

If you don't have experience with mains power or don't feel comfortable, please don't mess with it.  It could kill you and burn down your house just for spite. 

The mains power input connector (PW901) appears to be labeled with both the European color code: BLue and BRown, as well as the North American color code: WHite and BK = black.  Those all seem to suggest that the power supply might be a "universal" design that will operate on both mains voltages.

But even if the power supply survived the ordeal, it may have still toasted the main part of the circuit.  Even if you don't see any obvious signs of electrical trauma.

[zippydan]

I'm going to perform those tests you specified within the next hour and post them here.

In the meantime, some follow-up questions for my own curiosity. 

The idea that the power board is fine but that the next board in the circuit got fried was exactly my fear, but I would assume that the next circuit board would definitely run on some universal voltage like 5v or 12v or 24v, which the power board is responsible for providing by stepping the power down from whatever input it can handle (110v or 220v or both). 

So the only way that would make sense to have happened is if the power board was only designed to step down from 110v to 5v (for example), but instead received 220v, somehow survived, but then outputted a higher than expected step down voltage of like 10v, and this was enough to get the next board. 

Is that a correct basic level understanding?

Is that a plausible failure mode for this kind of equipment?  I would have expected that the board either could take 220v or not, and if it couldn't, then it would fry something in the power circuitry itself. 

Also, would a receiving 10v when 5v is expected typically be enough to fry a board?  I would expect a bigger difference needed to fry your typical PCB.  Maybe if it was expecting 24v and got 48v (I assume there are likely multiple voltage rails)? 

Is there any other way to tell conclusively from the design of the board or the ICs or the transformer or other circuitry whether it was meant to take 220v?

[zippydan]

You confirm that the fuse (F901) tests good (a very few ohms of resistance). 

The mains power input appears to be across the PW901 connector.  Is FL901 good?  What is the resistance across the two spark gaps?  They should each  be very low.  And in a similar manner across FL902?  From each of the "top" pins to the corresponding "bottom" pin?  (as shown in your photos).

The output appears to be those multiple wires coming out the end of the board. If you can safely plug the board into 110V mains, what voltage (if any?) do you measure across the output (C925)?

Results:

Fuse F901: Continuity Test solid tone, Resistance: 0.1 ohm
FL901 Spark Gaps: Top Pair: 0.5 ohm; Bottom Pair: 0.3 ohm
FL902 (Spark?) Gaps: Left Pair: 0.2 ohm; Right Pair: 0.2 ohm
C925 and C924: 23.2V DC

You will see responsible people like Dave and BigClive very carefully discharge (short out) that big input capacitor (100s of uF and 100s of volts) before messing with the SMPS board.

I just do this by holding a screwdriver (by the plastic handle) across the positive and negative leads of each of the two large capacitors after I'm finished testing and it is unplugged, correct?

Results:

Fuse F901: Continuity Test solid tone, Resistance: 0.1 ohm
FL901 Spark Gaps: Top Pair: 0.5 ohm; Bottom Pair: 0.3 ohm
FL902 (Spark?) Gaps: Left Pair: 0.2 ohm; Right Pair: 0.2 ohm
C925 and C924: 23.2V DC

So it seems the next board is expecting a higher low voltage (but still LV) of 24v.  If this power board is only designed for 110v, but somehow survived 220v, would a plausible failure mode be that it then outputted, what, 48V DC?  I'm not sure how that calculation works out.

Since it seems the power board is still working, despite being plugged into 220v, would it be worth plugging the power board into 220v again and retesting the C925 and C924 outputs and see what they give me?

[OwO]

The very least I would do is trace out the first stage of the power input, the rectifier and cap, to get an estimate of what voltage the PSU is designed for by looking at the capacitor ratings. If they bothered to use 600V caps then most likely the PSU is a universal design that supports 220V. I have never seen a SMPS without feedback control so outputting twice the nominal voltage at 220V input is very implausible unless something is damaged.

[Richard Crowley]

You are generally on the right track, but there are still too many unknowns to give any reliable answers.
In a way, it sounds like the SMPS is good and putting out 23.2V (close enough to a nominal 24V).
But, OTOH, it may suggest that the SMPS survived, but the rest of the circuit may be damaged.
Unfortunately, we don't know for sure how it is supposed to behave when working properly.

[zippydan]

The very least I would do is trace out the first stage of the power input, the rectifier and cap, to get an estimate of what voltage the PSU is designed for by looking at the capacitor ratings. If they bothered to use 600V caps then most likely the PSU is a universal design that supports 220V. I have never seen a SMPS without feedback control so outputting twice the nominal voltage at 220V input is very implausible unless something is damaged.

the two big blue caps in the middle are 460v 68uF, and the two medium sized black caps at the end are 35v 1000uF

Can you give me some direction as to how to trace the first stage of the power input, rectifier, and cap?

You are generally on the right track, but there are still too many unknowns to give any reliable answers.
In a way, it sounds like the SMPS is good and putting out 23.2V (close enough to a nominal 24V).
But, OTOH, it may suggest that the SMPS survived, but the rest of the circuit may be damaged.
Unfortunately, we don't know for sure how it is supposed to behave when working properly.

Do you have any suggestions for a next step of diagnosis?

Edit/Update: I did a search for the model number of the yellow transformer, part # EBJ62690001, and many websites seems to stock this as an LG replacement part.  One website gave the following specs: "120-240V 14Kv 0H 5Ma".  This seems promising for the theory that it is a universal power board, but not conclusive since who knows if the website is accurate and one part being universal doesn't necessarily mean the whole board is?

[OwO]

the two big blue caps in the middle are 460v 68uF, and the two medium sized black caps at the end are 35v 1000uF

Can you give me some direction as to how to trace the first stage of the power input, rectifier, and cap?

Sounds like a 220V rated PSU then. I would say everything is fine and the unit is simply defective.

You can take a picture of the wiring side of the PCB, print it out, then draw component symbols on it by looking at what is soldered on the board. Finally re-draw it as a schematic.

[zippydan]

You can take a picture of the wiring side of the PCB, print it out, then draw component symbols on it by looking at what is soldered on the board. Finally re-draw it as a schematic.

Trying to do this but it is nearly impossible to read some of the component markings because other components are blocking them and/or there is white goop covering them 

Also, does my previous edit give you any more indication of the likelihood of the board being universal?

[capt bullshot]

So the primary electrolytics are 450V rated and there's a reasonable voltage at the output. Nothing blew up while it was connected to 220V.
There's one conclusion: This PSU is not defective at all, and it is most probably a typical 90V ... 240V input type, having a flyback architecture.

From my experience, there's one good thing with this kind of PSU:
They work as desired, they don't work at all or they're violently blown - so this one is of the first kind.

Don't mind about 23.2V instead of 24V, internal power supplies of such kind of stuff use all kinds of unusal voltages.

[JimS]

From the traces on the bottom it looks like the output is basically a dual diode and filter caps.
I found the manual and it says that for the power input voltage to see sticker on the unit.
If it is labeled 110/120 I would guess that the supply put out way more than 24V and fried the controller.
If it is a 110-220 volt unit looks like it's a dud.

[OwO]

I see an optocoupler (IC902) so it definitely has feedback control. The situation described (supplying a higher voltage to downstream electronics) is highly unlikely.

[brabus]

The specs on the LG Website state: 100 to 240VAC.

In my very, very humble opinion, there is nothing wrong at all with the soundbar. Are you turning it on correctly? Is it visible via Bluetooth/WiFi? I don't know if these things need a specific configuration procedure; maybe it's listening to the TOSLINK or HDMI input...

[zippydan]

The specs on the LG Website state: 100 to 240VAC.

In my very, very humble opinion, there is nothing wrong at all with the soundbar. Are you turning it on correctly? Is it visible via Bluetooth/WiFi? I don't know if these things need a specific configuration procedure; maybe it's listening to the TOSLINK or HDMI input...

When plugged in, pressing the power button should light up the power LED and the display panel (according to the manual).  Instead, there is a beep and then nothing. 

And as far as looking for the right input, there is an input button to change the source and it does nothing also. 

It's looking more and more likely that the power board is good for 110v or 220v in which case I didn't fry it, but then it seems there is still something wrong with the soundbar...

Or I'm doing something wrong, but I can't imagine what should be more complex than simply pressing a power button.  Also, there is no response at all when trying to turn on the power using the remote.  That suggests to me that somehow the touch control panel is getting power, sending signal to the main board to power on, and getting no effect.  Similarly, the IR receiver seems to be non-functional.  That or maybe the batteries for the remote are bad?  Not likely consider they are new and alkalines don't really degrade...

I'm thinking I'm just going to try plugging the power board into 220v and test the C925 and C924 for output so I can be sure it still outputs 23.2v... any votes against?

[amyk]

If you happen to have another 24V DC supply  (or something close, like 19/20V from a laptop adapter) you could try connecting that instead, which will rule out the PSU as being at fault. Just be mindful of the polarity!

[CJay]

Stop messing about with it, the SK10Y LG soundbar has a universal PSU in it which will work from 100 to 264V input, speak to LG about warranty repair.

[zippydan]

I was tired of the uncertainty and all the signs pointed to it being a universal power supply. So I rolled the dice on the 95% chance.

Tested at input and got 224V AC.

Tested at C925 and C924 output and got 23.1V DC.

So, it looks like I didn't fry the speaker.  Lucky me.  Sorry for wasting your time, but the sticker on the back of the unit does say 110V 60Hz only and I generally expect those to be accurate.  (The country I'm in is 220V 60Hz standard btw.)

So this means I either don't know how to use this sound bar, or something else is wrong with it.  The second possibility is actually more troubling to me, because I don't think I can get warranty service where I am (I'll check tomorrow) and trying to troubleshoot the rest of the unit looks like it will be hellish.   

[Mechatrommer]

or you can pack them together again nicely before further or noticable damage is made making warranty claim inapplicable. you cant recognize an smps is for general 120-240V purpose, i havent heard any modern smps specifically made for certain geographical mains location, except the older pc atx psu smps design or they will have switch near power input for each 110 or 220V. trying to troubleshoot logic side of the circuit should pose more challenging feat. just return it to the seller and get a replacement before warranty void is inevitable.

[brabus]

The manual mentions an "AUTO POWER" function, I am still figuring out how it works. Have you tried playing with that? Is it possible to perform an Hardware reset?

[CJay]

or you can pack them together again nicely before further or noticable damage is made making warranty claim inapplicable. you cant recognize an smps is for general 120-240V purpose, i havent heard any modern smps specifically made for certain geographical mains location, except the older pc atx psu smps design or they will have switch near power input for each 110 or 220V. trying to troubleshoot logic side of the circuit should pose more challenging feat. just return it to the seller and get a replacement before warranty void is inevitable.

A good clue is the voltage rating of the main filter capacitor, if it's 385V or higher then it's likely universal but in this case, the manuals I found for this soundbar specifically state it's 100-264V input.

[zippydan]

Thanks for your help everybody.

Er, the unit is working now.

After I put everything back together I decided to try again and...  power LED lights up now.  Display lights up.  And I have sound.  I've also already got the unit connected to my WiFi and the firmware updated.

No idea what was wrong the first time.  Maybe unplugging and replugging the inter-PCB connectors fixed some flaky connection.  I have no idea.  I'm just happy the voltage sticker on the unit was wrong.  I'm happy I didn't fry the unit.  And I'm happy it is working now.

I also learned a bit more thanks to all of you here and that's always a positive.

The manual mentions an "AUTO POWER" function, I am still figuring out how it works. Have you tried playing with that?

I believe "auto power" is just a feature where the LG sound bar will automatically turn on and off when you turn the connected TV on and off.  This may be a feature that only works with an LG TV since there is some kind of proprietary LG-only communication over the optical line if you enable that setting on an LG TV.

[Mechatrommer]

Er, the unit is working now.
After I put everything back together I decided to try again and...  power LED lights up now.  Display lights up.  And I have sound.  I've als already got the unit connected to my WiFi and the firmware updated.
No idea what was wrong the first time.

maybe you are destined/born/encouraged to fix things. or the soundbar just wanted a little bit of attention from its new owner. usually my stuffs that got my attention will last much longer. some people say intruments have feeling, sometime i feel kind of that. but since no hard written proof on the fact, so i tend to not believe it. but made me wonder sometime. maybe its good for imaginative story telling or just for fun. sometime friend/relative asked me to fix their broken unit, but when i get there, all of sudden the unit is working fine without anybody touching it, so we made fun... its afraid of me