KEF LSX Teardown and Repair

[wouter]

It only took me a couple of months but my power supplies are back to working condition! It's been too long of a ride with a couple of unexpected issues (accidentally slipping with a set of tweezers and blowing up the working PSU, oh well!) to start-to-finish document everything that went wrong, but it was a fun project to work on!

If anyone is ever taking on a broken KEF PSU, definitely get yourself a cheap Optocoupler tester! The TO2 optocoupler tester helped me identify some of the issues I was running into, and a thermal camera ended up being a super helpful tool too. I ended up identifying into a couple of broken parts on the bottom of the PSU near the TI LM339 IC, such as a broken IC and a shorted capacitor.

I also noticed last week the gate driver on the front side (the side with all the capacitors) quickly heated up to 150C, causing the mosfet on the back to heat up as well. I replaced the gate driver and a diode besides it, since that one appeared to be shorted too. Which brings me to the question: does anyone happen to know what a good replacement for Z803 and U806 are? That's the missing pieces I need to permanently fix the PSU, since I borrowed them from the working PSU to test this one.

I think it's marked as

J3 4
   3

But I'm not entirely sure.

Okay, figured that part out. The J3 43 part is a 12V to 5V LDO, so I'll be replacing that with a TI LDO. It doesn't seem to use the most common pinout, but the TI LM3480IM3X-5.0 should be a good drop-in replacement.
My last struggle is finding a good replacement for the inductor (or ferrite bead?) on the back of the power supply:

It's a 1806-sized part, and I can basically only find ferrite beads in that size.. It measured as a 20uH inductor on my LCR bridge, with ~125-130mOhm series resistance:

This is definitely beyond the limits of my electrical engineering knowledge, so if anyone has good suggestions for a replacement part I'd love to hear it! I've tried emailing KEF and a local service center, to see if they might be willing to share some of their knowledge, but they either weren't willing or didn't have access to the service manual unfortunately. How did the other people on this thread get access to service manual snippets?

 

[wouter]

After some back and forth with KEF they shared that L802 is a Murata BLM41PG102SN1L.

 

[FraPia-62]

After some back and forth with KEF they shared that L802 is a Murata BLM41PG102SN1L.

Sorry for the late reply...
I guess that in the mean time you found the replacement, since the Murata BLM41PG102SN1L is rather easy to get (e.g. Mouser has it). Anyway if for some reason you need to procure an equivalent one, it is a ferrite choke, with an impedance = 1kOhm at 100MHz and max current=1.5A. The exact impedance is not particularly critical, just use the closest you can find.

 

[wouter]

Sorry for the late reply...
I guess that in the mean time you found the replacement, since the Murata BLM41PG102SN1L is rather easy to get (e.g. Mouser has it). Anyway if for some reason you need to procure an equivalent one, it is a ferrite choke, with an impedance = 1kOhm at 100MHz and max current=1.5A. The exact impedance is not particularly critical, just use the closest you can find.

All good! Just wanted to share the info I got from KEF in case it helps anyone else my replacement BLM41PG102SN1L (along with some other parts) is on it's way, so the power supply should be back to working order soon!

 

[lurks]

This is a great write up, thanks for your work.

I have a pair of KEF LSX and the master speaker has stopped powering on (no lights front or back, tried power cycling, various power outlets, and the second speaker cable - the second speaker does power).

The only other thing is that the remote is out of battery, but surely this does not prevent the master from powering on, right??? (I hate the lack of controls on these speakers and while they sound amazing, I wouldn't purchase again for this reason).

While I am not very experienced with electronics, I am a qualified electrician (domestic and commercial mains power) and consider myself somewhat capable with fault finding (at least for mains power) and I do have soldering experience.

I am thinking that I would like to open the speaker up and attempt to diagnose the problem with a test pen. Before I do, I wanted to check whether a likely cause could be a switch or a blown fuse that is easy enough to rectify/replace. Otherwise, if it's more complicated than this, I probably should just take it to the shop in case I break other components!

The speakers are out of warranty, so I don't mind fiddling. I thought I would give it a crack before taking it to a shop for diagnosis and repair.

 

[wouter]

This is a great write up, thanks for your work.

I have a pair of KEF LSX and the master speaker has stopped powering on (no lights front or back, tried power cycling, various power outlets, and the second speaker cable - the second speaker does power).

The only other thing is that the remote is out of battery, but surely this does not prevent the master from powering on, right??? (I hate the lack of controls on these speakers and while they sound amazing, I wouldn't purchase again for this reason).

While I am not very experienced with electronics, I am a qualified electrician (domestic and commercial mains power) and consider myself somewhat capable with fault finding (at least for mains power) and I do have soldering experience.

I am thinking that I would like to open the speaker up and attempt to diagnose the problem with a test pen. Before I do, I wanted to check whether a likely cause could be a switch or a blown fuse that is easy enough to rectify/replace. Otherwise, if it's more complicated than this, I probably should just take it to the shop in case I break other components!

The speakers are out of warranty, so I don't mind fiddling. I thought I would give it a crack before taking it to a shop for diagnosis and repair.

Welcome!

I haven't heard anyone mention similar issues, so I'm curious to see what's wrong with your unit. If I were you, I'd definitely open them up to check. There are multiple power rails, and the speakers not powering up does sound like something went wrong on the 12V power rail. It could very well be a cap that's gone bad.

You don't need the remote to power them on, the app should work regardless. You can try resetting them with the switch on the back, and they should broadcast a WiFi network to set them up. But if you're not getting any power LEDs, I'd be surprised if you'd get that far.

 

[FraPia-62]

If the master speaker gives no signs of life don't forget to check first the mains fuse (T4A, 250V, close to the mains connector) with an ohmmeter, then the standby power supply (the small transformer and 7-pin controller chip close to the main transformer) on the power supply PCB. Try to measure the voltage on the filter capacitor on the secondary side of the stand-by power supply. Don't try to measure the output of the controller chip (pin 4, the separate one), there are high voltage (~600V) peaks there, thus it can be rather dangerous! Let us know the results, maybe I can help a bit.

 

[lurks]

This is a great write up, thanks for your work.

I have a pair of KEF LSX and the master speaker has stopped powering on (no lights front or back, tried power cycling, various power outlets, and the second speaker cable - the second speaker does power).

The only other thing is that the remote is out of battery, but surely this does not prevent the master from powering on, right??? (I hate the lack of controls on these speakers and while they sound amazing, I wouldn't purchase again for this reason).

While I am not very experienced with electronics, I am a qualified electrician (domestic and commercial mains power) and consider myself somewhat capable with fault finding (at least for mains power) and I do have soldering experience.

I am thinking that I would like to open the speaker up and attempt to diagnose the problem with a test pen. Before I do, I wanted to check whether a likely cause could be a switch or a blown fuse that is easy enough to rectify/replace. Otherwise, if it's more complicated than this, I probably should just take it to the shop in case I break other components!

The speakers are out of warranty, so I don't mind fiddling. I thought I would give it a crack before taking it to a shop for diagnosis and repair.

I have sent my speaker in to a tech for assessment. They have indicated that there is a blown SMPS power supply circuit. They have quoted $605 AUD (which represents about 42% of the inital purchase price) to fix the speaker. This includes replacing the power supply PCB.

I am wondering how hard this would be to fix myself. Could anyone provide some insight into how hard this would be? If the SMPS is blown, could other parts be damaged? Can I buy the power supply PCB myself? Or should I cop the costs and have this done by a professional?

Cheers,

 

[FraPia-62]

I have sent my speaker in to a tech for assessment. They have indicated that there is a blown SMPS power supply circuit. They have quoted $605 AUD (which represents about 42% of the inital purchase price) to fix the speaker. This includes replacing the power supply PCB.

I am wondering how hard this would be to fix myself. Could anyone provide some insight into how hard this would be? If the SMPS is blown, could other parts be damaged? Can I buy the power supply PCB myself? Or should I cop the costs and have this done by a professional?

Cheers,

It really depends on the kind of failure. If the custom components (transformers) are still good, the repair is usually quite simple and the needed spares can mostly be purchased everywhere. If the transformers are bad, it is usually simpler to try to find the whole smps board, provided kef is willing to deliver it. The transformers alone are kind of unobtainium.
Be careful however that on the smps there are high voltages that are dangerous, on the drain of the transistor of the stand-by smps there are peaks of about 600V. If you are in doubt if you can repair the smps or not, most likely you should contact some professional to do the work.

 

[billqs]

I just got the dreaded red/orange flashing on LSX. Are the speakers good enough to bypass the electronics and run them passive? I know the LS50 are really good quality. I imagine these are enhanced by a DSP you would lose, but I have a McIntosh amp I could power them with.

 

[FraPia-62]

I just got the dreaded red/orange flashing on LSX. Are the speakers good enough to bypass the electronics and run them passive? I know the LS50 are really good quality. I imagine these are enhanced by a DSP you would lose, but I have a McIntosh amp I could power them with.

The LSX are biamped and use a X-over implemented in the DSP. If you want to run them passive you would need to design and assemble a passive LC X-over filter, then develop the EQ. It can be made, but I think you should rather try to repair them.

 

[Ebar]

Thanks to @FraPia-62 for the guide and to others who have posted their experiences and pictures in this thread. This is an excellent resource which evidently is helping quite a few of us who are facing this same issue. I have managed to disassemble my master speaker and found very similar damage to what others have reported.

For context, the lights on the front of my speaker were flashing alternating orange and red. I could connect to and configure the speakers via the KEF Control app, and attempt to play music, but the main speaker would not produce any sounds at all, while the secondary speaker would only play the chimes when powering on/off or changing source.

After disassembling, I found two separate areas of visible damage on opposite ends of the board.

1) The classic exploded L236 and cracked C433, with shorts to ground on C433, C434 and C435.
2) On the bottom end of the board, C441 has also exploded, apparently quite violently as it has destroyed the pads and produced a rather large crater. The cap itself had completely separated; I could just pick it up with a pair of tweezers. However, unlike others who have reported damage in this location, C442 and C443 are not visibly damaged and when tested with a multimeter are not shorted to ground.

I'm a total noob when it comes to SMD soldering and electronics in general, so I have no idea if the damage to the board is too great for me to repair, or if there is a problem further upstream which has caused these failures. But since these things are a paperweight anyway at this point, I'm planning to simply try to replace the damaged components and hope for the best! I'll report back with the results.

 

[ivayvr]

Another stellar example of KEF's exceptional engineering!
They probably saved 49 C per speaker by using the sub standard components and made thousands of people miserable!