KEF LSX Teardown and Repair

[FraPia-62]

Alright I guess it's not hard to see that L236 is at fault for me, too. Thanks a lot guys (and especially @FraPia-62!), without you I wouldn't have been able to find this I'll order the spare parts (probably also C434 next to 433 since it was quite in the blast zone), do my best to fix it and report back!
View attachment 394347
Good luck also to @Tokyoskies, I'm sure you'll fix it!

You should replace all 3 capacitors C433, C434 and C435 if you want to be on the safe side, although the shorted one is C433. The schematic diagram of the pre-regulator is on page 2, by @mar1in. Before mounting L236 check with an ohmmeter that there's no short-circuit, otherwise L236 will blow again. Good luck with the repair.

 

[Johsei]

So I was able to replace L238, C433, C434 & C435 and amazingly the speakers are working like a charm! A big thanks again for the great thread and the detailed instructions on page one!

For documentation and to help others, I changed
- L238 with Laird MI0805J102R-10 (0805, 1kOhm@100MHz)
- C433 with Würth 885012209073 (1210, 10uF, 50V)
- C434 with Kemet C0603X104K5RACAUTO (0603, 100nF, 50V)
- C435 with Würth 885382207006 (0805, 10nF, 50V)

Due to minimum order quantities I have quite a few components left (especially L238) so if anyone in or near Germany needs some, hit me up!

 

[Tokyoskies]

So I was able to replace L238, C433, C434 & C435 and amazingly the speakers are working like a charm! A big thanks again for the great thread and the detailed instructions on page one!

For documentation and to help others, I changed
- L238 with Laird MI0805J102R-10 (0805, 1kOhm@100MHz)
- C433 with Würth 885012209073 (1210, 10uF, 50V)
- C434 with Kemet C0603X104K5RACAUTO (0603, 100nF, 50V)
- C435 with Würth 885382207006 (0805, 10nF, 50V)

Due to minimum order quantities I have quite a few components left (especially L238) so if anyone in or near Germany needs some, hit me up!

Thats awesome news. Well done.

I also have resolved the issue and the speakers work really well again. After replacing D205 and D207, I found that C438 was also dead. Replacing this did the trick and the speakers are playing like new.

I also have A LOT of caps, diodes and resistors left, but I need them for all my other repairs. Got to fix my LS50 Wireless now.

 

[Andy1978]

Sorry for my english... I have same problem with my LSX. In service replaced L236 and C434, C435. Now i can play music about 10 minutes and blinking orange red. When i totally open speaker i can play few hours without problems. I see that q211 is very hot when i play music. Any ideas what should i check?

I make test. I use hair dryer on q211. When temp. Is up, voltage on output goes down from 13v to 8. When its about 8 blinking orange red. After few seconds speaker start playing. It looks like q211 need cooler or something after q211 take extra power

 

[Tokyoskies]

Sorry for my english... I have same problem with my LSX. In service replaced L236 and C434, C435. Now i can play music about 10 minutes and blinking orange red. When i totally open speaker i can play few hours without problems. I see that q211 is very hot when i play music. Any ideas what should i check?

I make test. I use hair dryer on q211. When temp. Is up, voltage on output goes down from 13v to 8. When its about 8 blinking orange red. After few seconds speaker start playing. It looks like q211 need cooler or something after q211 take extra power

Your English is fine. Where do you live?

Definitely sounds like a thermal issue, although those BCP56-10 can tolerate higher temperatures. Q211 has an input current of 30V on the collector, can you check the incoming voltage from L236 is 30V? R411, Z203 and C436 are in line with Q211. Check whether those are ok. R411 should have a 5kOhm resistance and protect Z203. If Z203 passes too much current, it may cause Q211 to heat up unnecessarily. So check the output voltage from Z203. Could also be a bad solder joint in that area. Those are not always easy to spot.

In my case Z203 was dead and needed replacement. Unfortunately I also had to replace Q211.
Can you also provide a photo of the area?

 

[Andy1978]

Your English is fine. Where do you live?

Definitely sounds like a thermal issue, although those BCP56-10 can tolerate higher temperatures. Q211 has an input current of 30V on the collector, can you check the incoming voltage from L236 is 30V? R411, Z203 and C436 are in line with Q211. Check whether those are ok. R411 should have a 5kOhm resistance and protect Z203. If Z203 passes too much current, it may cause Q211 to heat up unnecessarily. So check the output voltage from Z203. Could also be a bad solder joint in that area. Those are not always easy to spot.

In my case Z203 was dead and needed replacement. Unfortunately I also had to replace Q211.
Can you also provide a photo of the area?

I'm from Poland. Input voltage is 30v. I make photo tomorrow. I just closed speaker for test. I replace small cooler on BCP 56. It plays since half an hour. Well see what happens

Update: test faild after 45 minutes blinking orange red, but ... Its a little bit better than before. I don't know why bcp 56 is so hot.

Edit 2 : voltage on Z203 is strange. When i turn on speaker there is 22v and goes dawn in time. After 5 min there was 17v after 15 min. 14v.

 

[Tokyoskies]

I'm from Poland. Input voltage is 30v. I make photo tomorrow. I just closed speaker for test. I replace small cooler on BCP 56. It plays since half an hour. Well see what happens

Update: test faild after 45 minutes blinking orange red, but ... Its a little bit better than before. I don't know why bcp 56 is so hot.

Edit 2 : voltage on Z203 is strange. When i turn on speaker there is 22v and goes dawn in time. After 5 min there was 17v.

22V output from Z203 is correct. Can you check that Z203 is ok? It does look a bit weird. Not sure about that dark spot, as it doesn’t look like branding or marking to me.

Also please check C436 for damage.

 

[Andy1978]

22V output from Z203 is correct. Can you check that Z203 is ok? It does look a bit weird. Not sure about that dark spot, as it doesn’t look like branding or marking to me.

Also please check C436 for damage.

View attachment 396058

Z203 was dirty. I don't know what was that but now looks good. C 436 looks good too. When i check z203 there was 0.7v and 2v on other side. Its not good i think? Also voltage 22v on start and 13 after 30 minutes?

 

[Tokyoskies]

Hmmm, this all points toward a thermal issue coming from Q211, as you suspected in the beginning. I think KEF works in very tight tolerances with lower quality parts.

My guess is, as Q211 heats up R411 picks up that heat and raises its resistance, dropping the input voltage for Z203. I have seen Q211 running over 90 degree C on some forums, which is very questionable as this heat leaks through the PCB into nearby components. It might not damage them immediately, but can change their ratings.

Could be that you need to replace Q211. I had to do that in my case, as it was faulty. When measuring the base (pin1) with the positive lead and the emitter (pin3) with the negative lead, I had a 0.9V drop. Measuring base and collector (pin2) resulted in OL. If thats the case for you as well, then its faulty. Should measure aprox 0.5-0.6V for both readings.

Can you measure input voltage on pin 1 and the output voltage on pin 3 for both scenarios, so when speaker is working and when its orange/red? Also, please measure the input/output voltage on U20, the transistor close to Q211.

Also, please measure Q211 on the collector again (pin 2), after the voltage drops to 13V, I just want to make sure the incoming voltage from L236 is still 30V. Please measure on the collector for Q211 first and then on L236 to see if there is any difference. There are 3 capacitors we also need to consider.

 

[Andy1978]

Hmmm, this all points toward a thermal issue coming from Q211, as you suspected in the beginning. I think KEF works in very tight tolerances with lower quality parts.

My guess is, as Q211 heats up R411 picks up that heat and raises its resistance, dropping the input voltage for Z203. I have seen Q211 running over 90 degree C on some forums, which is very questionable as this heat leaks through the PCB into nearby components. It might not damage them immediately, but can change their ratings.

Could be that you need to replace Q211. I had to do that in my case, as it was faulty. When measuring the base (pin1) with the positive lead and the emitter (pin3) with the negative lead, I had a 0.9V drop. Measuring base and collector (pin2) resulted in OL. If thats the case for you as well, then its faulty. Should measure aprox 0.5-0.6V for both readings.

Can you measure input voltage on pin 1 and the output voltage on pin 3 for both scenarios, so when speaker is working and when its orange/red? Also, please measure the input/output voltage on U20, the transistor close to Q211.

Also, please measure Q211 on the collector again (pin 2), after the voltage drops to 13V, I just want to make sure the incoming voltage from L236 is still 30V. Please measure on the collector for Q211 first and then on L236 to see if there is any difference. There are 3 capacitors we also need to consider.

I check Q211 and pin 1-2 0.7v pin 1-3 0.7v pin 2-3 0.692v

VOltage q211
Pin 1 20v work fine 9.5v blinking
Pin 3 18.9 work fine 9v blinking
U20 in 18.9v work fine 9v blinking
U20 out 12.04v work fine 9v blinking

Pin 3 and L236 have always satbile 30v

I think problem is change 30V to 18V by Q211. Problem is temperature... question is which part make problem???

 

[Tokyoskies]

In my case, I replaced Z203 since it was shorted anyway (it was beeping in continuity on my multimeter). I did not have 22V, so I replaced it with a 20V 500mW. Works fine though. Unfortunately, I also had to replace Q211, as I mentioned earlier.

For you, since output current drops after Z203, I would probably start there. Just make sure you have 5kOhm on R411. Its a strange situation though.

 

[Andy1978]

W moim przypadku wymieniłem Z203, ponieważ i tak był zwarty (na moim multimetrze piszczał w ciągłości). Nie miałem 22 V, więc wymieniłem go na 20 V 500 mW. Działa jednak dobrze. Niestety, musiałem również wymienić Q211, jak wspomniałem wcześniej.

Dla Ciebie, ponieważ prąd wyjściowy spada po Z203, prawdopodobnie zacząłbym od tego. Upewnij się tylko, że masz 5kOhm na R411. To jednak dziwna sytuacja.

Most strange thing is that - spekaer play few hour without problems but it must be like on picture

 

[Tokyoskies]

Most strange thing is that - spekaer play few hour without problems but it must be like on picture

Did you verify R411? That resistor is essential for Z203 to receive the correct voltage.

Yes, if the issue is thermal, it makes sense that it can play better outside of the case. How hot is Q211? Can you somehow measure that?

I think I remember that Zener diodes are also affected by heat. But I cannot remember if voltage drops or raises with higher heat. If you can check the temperature of Q211 and Z203, that would be cool.

 

[Andy1978]

Did you verify R411? That resistor is essential for Z203 to receive the correct voltage.

Yes, if the issue is thermal, it makes sense that it can play better outside of the case. How hot is Q211? Can you somehow measure that?

I think I remember that Zener diodes are also affected by heat. But I cannot remember if voltage drops or raises with higher heat. If you can check the temperature of Q211 and Z203, that would be cool.

R411 4.8kohm. i try to check temperature but i have to get temp. Meter. I have creazy idea. If in ma case problem is dc regulator (its too hot) maybe i can do something like that on pictures?

 

[Tokyoskies]

If you think that Q211 runs far too hot, you could try a heatsink on it. Just a small one, like the ones I use in my Raspberry Pi.

 

[Andy1978]

If you think that Q211 runs far too hot, you could try a heatsink on it. Just a small one, like the ones I use in my Raspberry Pi.

View attachment 396343

Im sure problem is too high temperature near Q211. All parts looks good. I tried use heatsink, but that was really small. First i try to buy bigger heatsink. If its not gonna work, i mount dc/dc regulator. It have to work finally

 

[ivayvr]

It is scary how much pain KEF caused to so many people! All that for probably saving less than a dollar per unit. I was not aware that even LS50 wireless is not very reliable.
At one point I was considering the LSX and for the money, you can buy a pair of Genelec 8030 or Genelec 8020 and WIM Pro Plus!
As a side note, I would never buy any "all in" active speaker because of the complexity involved and probability that one element of it will fail or become obsolete.

 

[Andy1978]

Straszne, ile bólu KEF sprawił tak wielu ludziom! Wszystko to prawdopodobnie za mniej niż dolara oszczędności na jednostkę. Nie wiedziałem, że nawet LS50 wireless nie jest zbyt niezawodny.
W pewnym momencie rozważałem LSX, a za tę cenę można kupić parę Genelec 8030 lub Genelec 8020 i WIM Pro Plus!
Jako ciekawostkę dodam, że nigdy nie kupiłbym żadnego aktywnego głośnika typu „all in” ze względu na jego złożoność i prawdopodobieństwo, że któryś z elementów ulegnie awarii lub stanie się przestarzały.

Lsx is my first and last all in one. I have also kef IQ 70 + powernode+ nordost superflatline+ woofer kef and that play awesome.