Help Needed with LG Subwoofer

[Hyra]

So, here's my dilemma. I recently picked up an LG "Wireless Active Subwoofer" Model S33A1-D (The 40W version) at a garage sale and realized that there is no normal way to connect it to an audio source without the soundbar. Since the family had sold the soundbar a long time ago, I wanted to find another solution that didn't involve outright buying another soundbar. Any ideas about how I can use the ESP8266 (https://www.aliexpress.com/item/New-Wireless-module-NodeMcu-Lua-WIFI-Internet-of-Things-development-board-based-ESP8266-with-pcb-Antenna/32656775273.html) To broadcast either from the computer it's attached to or from an sd card reader a signal that can then be played by the sub?

(FCC specs on the wifi card can be found here https://fccid.io/BEJ9QK-R2)

 

EDIT: If you have any other cheap solutions feel free to share them!

Edited March 24, 2019 by UnreliablyGood

[Bitter]

Open it up, find the line in from the wireless module to the amplifier, connect a standard RCA cable to it, now you have a wired sub. It likely uses some proprietary wireless signaling you won't be able to duplicate without that compatible sound bar.

[Hyra]

Just now, Bitter said:

Open it up, find the line in from the wireless module to the amplifier, connect a standard RCA cable to it, now you have a wired sub. It likely uses some proprietary wireless signaling you won't be able to duplicate without that compatible sound bar.

how would I find the line in for the sub? it seems to be connected as a full wireless card to a computer board

[Bitter]

Can you post some good photos of the cards and where they're connected?

 

 

Looks like there's 3 boards, one small at the far right is some kind of wireless card, then a 'brain' card which may contain the amp circuitry, and a power supply card which might contain the amp circuitry. It's hard to tell which the speaker connects to, but you should be able to trace backward to find the amp portion of the board which usually takes in an analog signal from the processor.

[Hyra]

Here's the assembly:

Then the power supply/amp, appears to server both purposes

Then the "brain" or motherboard, as it seems

and the wifi card, I can provide ant serial codes as needed.

[Bitter]

So does the speaker connect to the big two pin white header on the 'brain' board? If so then it's not going to be possible or easily possible to do what I said, it will be a processor that's taking the signal and spitting it out on some traces to the digital amp that's then dropping it to the speaker as analog.

[Hyra]

2 minutes ago, Bitter said:

So does the speaker connect to the big two pin white header on the 'brain' board? If so then it's not going to be possible or easily possible to do what I said, it will be a processor that's taking the signal and spitting it out on some traces to the digital amp that's then dropping it to the speaker as analog.

So the plug connects into the large white header on the PSU, and the brain board has the medium white and small brown connectors for what I'm assuming are the speakers in the unit.

[Bitter]

Wait, it has two speakers? I thought this was just the subwoofer unit?

[Hyra]

Just now, Bitter said:

Wait, it has two speakers? I thought this was just the subwoofer unit?

It has one 3pin connector and one big white two pins for the brain, and yes it appears to have two speakers.

[Bitter]

The speaker is using that small brown 3 pin connector? I'd have expected the bigger white two pin for the speaker.

[Hyra]

These are the two connectors that go into the body of the speaker and connect to the brain. I can't figure out how to get into it without doing considerable damage to the wood.

[Bitter]

Usually speakers will screw in from the front behind the grill, the 3 wire looks more like a 2 color status LED. Odd that the 2 wire uses such different wire gauges.

[Hyra]

2 hours ago, Bitter said:

Usually speakers will screw in from the front behind the grill, the 3 wire looks more like a 2 color status LED. Odd that the 2 wire uses such different wire gauges.

So do you have any insight on how I would communicate with the subwoofer through the ESP8266? Do I use analog or digital? Do you think that it needs some kind of key to communicate? How would I find what specific frequency it broadcasts on?

 

EDIT: I believe now that the brown three wire connector is the status LED on the front that flashes red and green

Edited March 24, 2019 by UnreliablyGood

[Bitter]

If you can find which chip is the DSP that drops the wireless digital signal to an analog one for amplification and find the spec sheet or find the amp chip and it's spec sheet you might be able to solder on some wires to feed in analog audio at the right levels. It's probably using some specific proprietary wireless signalling to send audio from the bar to the sub. Maybe some data sheet somewhere might have some info, but the wireless radio info will only tell you what bands and frequency, not the setup and signaling of the connection.

[Unimportant]

It's probably a class D amplifier in which case it's possible the digital signal is never converted to analog before sending it to the amplifier. They could use the digital signal directly to modulate the PWM.

[Bitter]

48 minutes ago, Unimportant said:

It's probably a class D amplifier in which case it's possible the digital signal is never converted to analog before sending it to the amplifier. They could use the digital signal directly to modulate the PWM.

That's a very good point and likely the case, in which there is no way to use any of the electronics present. Gut the parts and bolt a plate amp to the back of the enclosure and call it a day.

https://www.parts-express.com/dayton-audio-sa25-25w-subwoofer-plate-amplifier--300-782

40W is probably peak power, who knows what the RMS wattage is but I can almost guarantee that this is a better amplifier. You need a 5.25 by 5.25 inch hole in the back or side and about 2.6 inches deep, I don't know what that enclosure looks like.

[mariushm]

It's really unlikely you're gonna get that working

That's not just a plain wireless card, it has a processor with bluetooth that receives signal from the main unit, decodes it and reformats it into I2S , I2C or SPI and sends this digital stream to that Pulsus chip in the center of the circuit board.

That's basically a sound processor and class d audio amplifier in a package - YOu can search for Pulsus PS9854

I could only find the Pulsus 9850 which is an 8 channel amplifier, so the 9854 is probably a 4 channel or 2.1 version, a cheaper model of the big one.

Here's the Pulsus 9850 datasheet: PS9850-Brief-Data-sheet.pdf

 

I suspect they use this chip because it has built in equalizer and "bass management" and they probably configure it in bridge mode (join two outputs together to get a more powerful single speaker output) ... there's some chips around it that look like eeprom chips, so that pulsus may read its configuration/preset from one of those chips and then the "wireless" card just hits the reset and starts sending audio data packets to the amp chip

 

Still it's not a total loss / waste ... the power supply part looks solid and you have the pinout right by the connector ... can't see it quite well but it looks like 3 wires are ground, 3 wires are voltage and one wire is "control" or something like that .. i'd guess it's "power on/standby" - basically you probably connect that wire to ground to turn on the power supply fully.

So you could buy some other mono class D amplifier and replace the audio board inside with your audio amp and use the power supply from the bar .. just get a circuit board that can handle the voltage of the power supply and the impedance of the speaker.

 

For example, if the power supply outputs less than 24v, then this could output up to 60w and it's easy to wire up : https://www.ebay.com/itm/TPA3118-High-Power-Audio-Amplifier-Board-Mono-60W-BTL-AMP-DC-8-24V-D-Class/392265009168

Another model : https://www.ebay.com/itm/DC-12V-24V-TDA7492MV-Mono-50W-Class-D-Audio-Power-Amplifier-Board-Amp-Module/323296765773?

 

[canbulatemre]

Hi. The main PSU of my device does not work. Total 4 missing. How do I learn part names?

[Unimportant]

4 hours ago, canbulatemre said:

Hi. The main PSU of my device does not work. Total 4 missing. How do I learn part names?

Are you sure someone removed those parts? Having unpopulated positions is not uncommon.

[mariushm]

As Unimportant says, some components are missing from the factory.  The locations are there in order to reuse the base board with higher power models, or if some markets demand stricter output quality, for example.

 

In your case, you can see in the bottom right corner that a jumper link ( a piece of wire) configures the power supply between two groups of models and two components have different values, depending on where the jumper link is.

In your current configuration, the C913 position is listed as NC, which means No connection, so it's on purpose left empty.

 

If a part was blown or damaged, you would still see the leads or some solder residue on the other side of the circuit board.

 

I would be concerned about the component right by the side of the transformer (the yellow big block), above the D901  text.

That's a diode or a set of diodes which are critical for the power supply, can't work without them.

It looks like it may have blown up, or there was another diode or another component right above it (I can't tell the text because of the Flash).

I say something was probably wrong there because you see carbon or some signs of overheating there.

 

Also, just replacing parts is not enough, some components may be damaged without showing signs of failure... you must test before blindly replacing.

I'd use a multimeter to check the fuse for continuity, then use it in diode mode to check the bridge rectifier (BD901 in top right corner), then test the diodes D901 (right of transformer) and D905 (below bridge rectifier)  and then I'd test the mosfets for shorts using the diode mode  (they're the chips on the heatsinks -  well, they're probably mosfets, could be offline switcher chips which contain a mosfet)

 

Anyway. the strong suspect for me would be D901 and whatever was above it, I'd start from there.

[canbulatemre]

We removed the missing electronic parts to replace them but then we lost them

[pumukli]

Sziasztok, ma kaptam javításra egyet, még gyárilag van őszerakva. Van egy alkatrész ami kidúrrant, nem lehet leólvasni az értékét.Vagy egy kapcsolási rajz kellene, vagy ha valaki meg tudná mondani a C911 értékét az jó lenne. A rajz pedig óriási.

Ngyon megköszönném segítségeteket.

[skunk8pe]

I too picked one of these subs up (Goodwill $5) and was hoping to throw in the back of my jeep wrangler.

 

I read thought the previous posts and came to the decision that I would just remove the boards and slap a amp board in it as suggested above. While removing the boards I found buss designators and test points printed on the underside of the processing board and proprietary kerfuckkle bluetooth board. I know very little about digital signal processing but was hoping that the pics below could shed some new light and hopefully lead to being able to shoehorn a line in somewhere...

 

Yes, I am well aware I could just go and buy a cheap-ish amp but what fun is in that?

 

edit:

I know absolutely jack about digital audio but in googling the buss i2c buss lines I found this..

https://www.diyaudio.com/forums/digital-line-level/206745-i2s-nomenclature.html

Might make sense to someone here.

 

[artuc]

Just skimmed through previous replies but the general concern is that the Bluetooth (?) sub board with ribbon cable would be a digital audio signal back to the mainboard.

 

Now depending on the ICs on the board, there may be a dedicated DAC, in which case you could potentially tap in where that analog conversion is. However the amplifier IC may take a digital signal straight in and it may go through crossover stages, etc. etc.

 

May be possible, but difficult to trace out based purely on a photo even for someone knowledgeable enough.

[deroo]

On 11/21/2019 at 6:24 PM, mariushm said:

As Unimportant says, some components are missing from the factory.  The locations are there in order to reuse the base board with higher power models, or if some markets demand stricter output quality, for example.

 

In your case, you can see in the bottom right corner that a jumper link ( a piece of wire) configures the power supply between two groups of models and two components have different values, depending on where the jumper link is.

In your current configuration, the C913 position is listed as NC, which means No connection, so it's on purpose left empty.

 

If a part was blown or damaged, you would still see the leads or some solder residue on the other side of the circuit board.

 

I would be concerned about the component right by the side of the transformer (the yellow big block), above the D901  text.

That's a diode or a set of diodes which are critical for the power supply, can't work without them.

It looks like it may have blown up, or there was another diode or another component right above it (I can't tell the text because of the Flash).

I say something was probably wrong there because you see carbon or some signs of overheating there.

 

Also, just replacing parts is not enough, some components may be damaged without showing signs of failure... you must test before blindly replacing.

I'd use a multimeter to check the fuse for continuity, then use it in diode mode to check the bridge rectifier (BD901 in top right corner), then test the diodes D901 (right of transformer) and D905 (below bridge rectifier)  and then I'd test the mosfets for shorts using the diode mode  (they're the chips on the heatsinks -  well, they're probably mosfets, could be offline switcher chips which contain a mosfet)

 

Anyway. the strong suspect for me would be D901 and whatever was above it, I'd start from there.

What an awesome reply, I just wish I knew what to do with that info. I too have an S33A1-D subwoofer that won’t power up. I opened up the unit and can see some overheating has occurred. I suspect the best course of action would be to replace the whole PSU board, I contacted LG but they won’t supply one. So, trying to now source a board. If you happen to know where I can get one I’d appreciate it. It is an old soundbar and woofer, but it was given to me by my dad who is now gone and I can’t yet part with it. If I can breathe a bit more life into it I’d be really pleased