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Fixing LC2 dimmer IR issue

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Franck
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Franck Posted: Thu, Sep 11 2014 9:18 PM

Hi all. I've ordered some days ago a faulty LC2 dimmer at good price from a guy of this forum (thanks to him).

symptoms: the touch was working but not the IR
Here is my repair story if it can help someone.

here is the faulty board


you can see the IR board on a little PCB.

the system is connected to the main so you must disconnect it from the mainboard to work on it


and use a power supply to safely test the circuit.

the PCB uses 3 pins. two for power and one for received IR burst.
the ground is the black the red is the +5v and the white is the output


here is the schematic from the service manual

using a scope and after powering the circuit under 5v I've got this trace at the output

With or without IR light from a remote there's some random burst -> stange so I'm trying to find where the IR light is stopped.

Here is the trace at the point A when pushing a button on the remote




Well the bursts are received by the photodiodes.

now at the point B i've got


So the discrete 455KHz tuned amplifier works too

and now at the point C


huh! nothing! Huston? we have a problem! the U2506 input has an offset and seems to have a low input impedance.....

ok now let's check the other signals. test the ref voltage at the point D


Wow! noisy ref voltage! even if we are near the 2.35v value from the datasheet there's definitively something wrong!

looking closely to the PCB something was strange:

with the binocular

the capacitor pin was corroded -> electrolyte leakage! here is the culprit! The leakage has  corroded the capacitor copper pin and the ref voltage is no more filtered
Eeven taking lot of care when removing it the ground pin was torn from the PCB

the capacitors are two 22uF 6.3V with 4mm diameter

and 5.5mm heigh

I've found a good replacement from Panasonic FK serie 105°C even if the original one is a standard (not low ESR and 85°C)



after modifying the copper to reconnect the ground of the capacitor (removing green varnish)


the capacitors were replaced with a ground wire

now here is the reference voltage measurement at point D



Well! much better!!

and now the output signal of the IR board with IR signals coming from the beolink1000



It's alive! the circuit is now working!

we can close the metal shield




put it back on the main PCB and voilà!

the dimmer is now working well \o/

I hope this post will help someone :)


I love when a plan comes together

Beogram 4002 / Beocenter 9000 / Beocenter 9500 / RL140 / Beolink 1000 / Beolink 4

Rivenflush
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Very very nice - glad to see you got it working! Now it's time for the other one Smile

My B&O products: Beosound 9000, Beosound 2300, Beosound Century, Beolab 8000, Beolab 6000, Beolab 4000 x2, Beolab 3500, Beolab 2000, Beolab 10, Beolink Active x2, Beotime, Beo5 x2, Beo4, A9 keyring x2, LC2 dimmer x6 and growing....

Franck
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Franck replied on Fri, Sep 12 2014 8:43 AM

the other one has only the connection terminal broken so it's easy to fix :)

I love when a plan comes together

Beogram 4002 / Beocenter 9000 / Beocenter 9500 / RL140 / Beolink 1000 / Beolink 4

RaMaBo
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RaMaBo replied on Mon, Dec 12 2016 1:31 PM

Hi Franck,

thank you for your very detailed analysis of the fault! Yes - thumbs up

 

It helped me to solve a similar problem with a LCS9000 / BeoLab3500 i bought.

It also didn't react to any IR command but the two touch fields on the display reacted when touched.

The same filterering capacitor on Pin 3 was dead, the voltage at the IC was also not straight but flattering around. After replacing the 22µF / 6.3V with a new SMD Capacitor it worked very well.

Now there's just one problem left in the audio part with a crackling sound but i guess it's also a dead SMD capacitor.

 

Ralph-Marcus

Keith Saunders
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Franck,

Your post is a very good description of the test process and repair of the LC2 and as you know these capacitors are quite a common problem.

Regards Keith....

ProGram
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ProGram replied on Tue, Dec 13 2016 8:13 AM
These smd electrolytics are so mean! I remember those days when the capstan motor of the VX5000 failed...
Beolab1
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Beolab1 replied on Thu, May 10 2018 3:26 PM

Hello all,

I have an LC2 that gave up after a few days of use. It was on the ceiling and connected to a hanging lamp. There is an issue with this particular power outlet, which seems to have affected the LC2. This issue will have to be fixed by an electrician, but I was wondering if anybody would have an idea what’s wrong with the LC2 and if I could fix the dimmer.

I took it apart, the fuse is okay. No signs of any burning or capacitor leaks. I connected the mains and a lamp, but no sign of power coming out. When I touch the outgoing power cable connecting screw with a voltage meter, it does not light up. The funny thing is, when I disconnect the lamp and touch the outgoing power cable connecting screw with a voltage meter, the voltage meter does light up. So when no lamp is connected, it seems to be doing something. Does anybody have an idea what this could be?

Thank you very much in advance for your assistance!

 

 

 

RaMaBo
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RaMaBo replied on Fri, May 11 2018 11:52 AM

Hi,

 

the described 'measurement is correct and just normal:

When the lamp is connected to the output connectors there's nearly a short between 'N' and 'L' by the lamp, so you won't get a readout on your multimeter.

If no lamp connected there's no 'short' between the 'N' and 'L' lines and the high impedance of the multimeter creates the voltage you can see now. The current that's running into the multimeter is so low that nothing will happen to you and your multimeter.

 

The same is for your small 25 W lamp: The LC2 needs at least 40W to work as designed!

So to test your LC2 you should 'load' it with 40W or more.

 

Ralph-Marcus

marexy
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marexy replied on Tue, Sep 18 2018 12:19 PM

Hi

Can any send link where to find service manula for LC2 ?

Thanks :)

 

 

BeoIce
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BeoIce replied on Tue, Sep 18 2018 1:31 PM

Everywhere those damn dead capacitors which cause trouble because they all use the cheap 85°C ones instead of the slightly more expensive 105°C capacitors.

BeoSound 9000 MK3, BeoLab 8000, BeoLab 6000, BeoLab 3500, LCS9000, BeoLab 11, BeoLab 7.2, BeoLab 7.1, Beolab 4 PC, BeoCenter 2300, BeoSound Century, BeoSound 8, Beosound 2, BeoVision 7-40 MK2 , BeoVision 7-32 MK3, BeoVision 6-22, BeoVision 4-42, BeoMedia 1, BeoCom 4, BeoLink 1000, BeoLink 5, BeoLink 4 & BeoTime

marexy
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marexy replied on Tue, Sep 18 2018 2:10 PM

I change all of them...not working.

Have 5v on the IR board.

So next step is to go step by step that is why i need service manual.

I do not wist to thow it in to scrap.

 

 

marexy
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marexy replied on Wed, Sep 19 2018 8:49 AM

I can not find online service manual.

Have somenoe form you in PDF ?

Thanks

RaMaBo
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RaMaBo replied on Wed, Sep 19 2018 10:26 AM

Does the dimmer show any reaction when touching the dome?

 

If so it's the SMD capacitor which 'Frank' (the thread starter) showed in his excellent failure analysis.

I had the same fault on the IR Receiver part in a BeoLab 3500, a _non_ constant voltage at pin 3 of the AM receiver chip. Changing the buffer capacitor solved the issue, the reference voltage on pin 3 was absolutely flat and the IR receiving was fine.

 

The touch function can also be tested when the dome is removed. There's a small black rubber hose sticking through the plastic frame. it connects the dome with the corresonding circuit on the mainboard. You can touch it with your bare fingers without any harm. This rubber piece is small and necessary for the touch function, so keep an eye on it, to not loose it,

 

 

Ralph-Marcus

marexy
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marexy replied on Wed, Sep 19 2018 10:39 AM

Hi

I have 4,8V on the IR  PCB

When i pug in to 230V the light bulb 60W goes on and that is it.

Not possible to do anything more.

There is no reaction to either manual control or remote.
Maybe it's a non-working triac?

That is why i'm looking for shematics manuals.


 

marexy
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marexy replied on Thu, Sep 20 2018 8:39 AM

problem found :)

triac not working so i need to repalace with sensitive gate triac.

it should be Igt 5-10mA

did try GT 138-600 but it only worked if warm as it's only Igt 25mA.

 

RaMaBo
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RaMaBo replied on Thu, Sep 20 2018 11:31 AM

Great, get a BTA06-600 TWRG from farnell.com for 78p and everything should be fine then!

Even if it's 'only' 600V it should work without any problems. If you want to be on the absolutely save side try to get a   BTA06-800 TWRG  which supports up to 800V.

 

But the Triac has to be one with the suffix TWRG (if it is from ST) to fulfil the 5mA Igt limit.

Ralph-Marcus

marexy
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marexy replied on Thu, Sep 20 2018 11:35 AM

hi

I purchase BT138-600E with Igt 10mA, hope it's ok :)

Thanks for tip :)

marexy
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marexy replied on Tue, Sep 25 2018 7:45 AM

done :)

BT138-600E working just fine :)

 

cpucomp
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cpucomp replied on Fri, Jan 4 2019 2:18 PM

Guten Tag Frank

Ich habe das gleiche Problem mit einem LCS 9000. Ich hoffe , Du kannst mir weiterhelfen: Die Frontabdeckungen sind weg , vor mir liegen die 3 Platinen 

1: ist die Deckelplatine mit dem Display -arrey drauf, da ist auch die rote Diode eingesteckt und die Infrarot.Dioden eingehackt ist der rechteckige Plastikrahmen. Ein Flachbandkabelanschluss.

2. darunter liegend links ein kleinere Platine mit drei Flachbandkabelanschluss

3.rechts davon eine quadratische (ca. 6x6 cm ) abgeschirmte Platine mit einem Flachbandkabelanschluss.

Welche der beschriebenen Platinen ist die Platine, wo ich den SMD Capacitor finden kann .

waren es 22uF / 6V ?

Besten Dank für Deine Hilfestellung

 

MFG Ueli Pfister 

RaMaBo
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RaMaBo replied on Fri, Jan 4 2019 6:31 PM

Hi,

concerning the non IR receiving LCS9000 / Beolab 3500:

 

It's the board with the display, IR receiving diodes, the touch switch (Timer and Mute) mounted.

There sits a  chip in the lower left corner which has a printing on it: U2506B

This is the same chip as in the LC2 dimmer. Now read the excellent fault finding description of Frank and do some transfer work. This leads you to the SMD capacitor C18 which is connected to Pin3 on the U2506.

The original one is a 22µF 6,3V so get the same and replace the old one very carefully.

Hope this helps

 

Und das ganze mittels Google Translator:

<------

Hallo,

in Bezug auf den Nicht-IR-Empfang LCS9000 / Beolab 3500:


Es ist die Platine mit Anzeige, IR-Empfangsdioden, dem Berührungsschalter (Timer und Stummschaltung).

In der unteren linken Ecke befindet sich ein Chip mit einem Aufdruck: U2506B

Dies ist derselbe Chip wie beim LC2-Dimmer. Lesen Sie nun die ausgezeichnete Fehlersuchbeschreibung von Frank und führen Sie einige Übertragungsarbeiten durch. Dies führt Sie zum SMD-Kondensator C18, der an Pin3 des U2506 angeschlossen ist.

Das Original ist ein 22µF 6,3V, also holen Sie sich das gleiche und ersetzen Sie das alte sehr sorgfältig.

Hoffe das hilft

<--------

Ralph-Marcus

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