The Workbench

Re: LC2 repairs

Keith Saunders — Fri, 24 Oct 2008 07:14:41 GMT

Geoff,

I am very pleased to see you managed to get it resolved to your satisfaction and you are now the LC2 expert !!

Re: LC2 repairs

geearr — Fri, 24 Oct 2008 07:03:40 GMT

Just a note to complete this saga.

B&O were initially unable to trace the part using the part number 1740665. However, they investigated their system and came back with the new part number 8000664 for the PCB1. I ordered this part at a cost of A$44 and it arrived fairly quickly.

The new board has much smaller components and four IR detectors instead of two, see photo attached.

To take the board off, I had to unsolder and remove the top metal plate, unsolder the three connections on the small top board, lift off the top board and then remove the bottom plate. Reassembly was simply the reverse of the above, the main difficulty being the soldering of the very small connections.

When the LC2 was completely put back together, it worked first time so our conclusion that the IR detectors or other components on the IR receiver PCB were faulty, was correct.

I have now saved an LC2 from the scrap bin, thanks to everyone concerned for your assistance.

Geoff

Re: LC2 repairs

geearr — Mon, 06 Oct 2008 07:02:13 GMT

This is a side view of the IR receiver PCB showing the three heavy connecting pins. No sign of coloured wires here??

Re: LC2 repairs

geearr — Mon, 06 Oct 2008 06:58:11 GMT

This is a view of the LC2 showing the position of the two diodes. Hope the pic attaches OK

Re: LC2 repairs

Keith Saunders — Mon, 06 Oct 2008 01:41:34 GMT

Geoff,

To attach a photo to each posting, when you reply at the top you will see four "tabs" clcik the "options" tab, then use the file/update button to add the picture.

Re: LC2 repairs

geearr — Sun, 05 Oct 2008 23:59:56 GMT

Hi Keith

Many thanks for all of the information on the LC2, I have now got a better idea of what I am dealing with and the following is now clear:

The dome, the spiders web and the small plastic tube are all important in the touch control functionality. Since that is working OK, I shouldn’t be having any problems with those items.
The IR functionality is most likely going to depend on the performance of the small IR receiver PCB. It is therefore possible that my problem is related to some faulty components on that board.

I have had another look at the LC2 internals and the packaging that came with it and have found the following:

I cannot find a “Type” number written on the LC2 but assume that it is 2130 for the EU market. I am not sure what your Type 7406 refers to.

All of the three packaging boxes have the same “model number”, 1213125, but I don’t know if this helps at all.

The earliest serial number from the three units is 14708428 and this might be useful for identifying whether some of the production changes have been applied or not.

The PCB appears to be fitted with two diodes at right angles so, from your description, this could be a reasonably current model.

I don’t have a PCB serial number that I can see but it might be underneath.

In your text to me, you mentioned that the cable to the IR receiver is brown, green and white. I cannot find any cables with that sort of colouring anywhere.

The IR receiver PCB seems to be joined to the other board by three heavy pins. I am not sure whether these just pull apart or whether I need to unsolder the pins from the top. Do you know the answer to that one?

Today, I contacted our local B&O agent and asked them to get a price for the part that you specified, 1740665. I assume that this refers to the updated replacement for the IR receiver PCB. Apparently their computers show that this part is not available, discontinued or something like that. Is it possible to check on the systems in the northern hemisphere and confirm that the part number is valid and the part is still available. If it is, I will need a contact to help supply it.

I have certainly learnt a lot about LC2’s over the last few weeks. Thanks for the invaluable help and I hope that we can continue to try and get this unit working once again.

I wanted to attach some photos but it seems that this is not an obvious task. I will have to work on that one.

Geoff

Re: LC2 repairs

Keith Saunders — Sun, 05 Oct 2008 08:22:43 GMT

Geoff,

In your posting you asked how the dome sensor works and the following is an overview:-

The core principles of the LC2 dome sensor are based on one of Faraday's laws related to capacitance which is measured in Farads after Michael Faraday and capacitance is normally quoted in MicroFarads (10 to the minus 6) or PicoFarads (10 to the minus 12)

In the case of the LC2 we are talking about capacitances of between 25 and 75 Pico Farads and the dome whilst made of plastic is part of the dielectric of the capacitor. Below the plastic dome is what looks like normal rubber, but is in fact conducting rubber like material which joins the dome and the IR PCB. To stop stray interference/capacitance the IR board are as near as possible to the plastic dome and if not fitted correctly will stop the "touch" from working.

Below is the circuit which the Dome (Capacitor) is connected too.

The ST6220 microprocessor produces a strobe signal and when you touch the dome a capacitance is produced which switches the transistor TR3 and provides a pulse stream back to the microprocessor. Depending of how long you touch the dome defines how many strobe pulses goes back to the microprocessor. The processor counts the pulses to determine if you are switching the light off/on or dimming etc.

I think I covered the other points in reply to your PM to me..

Re: LC2 repairs

mobeyone — Tue, 30 Sep 2008 02:53:45 GMT

I was told once that the dome is prone to failure which affects the ir/touch functionality? can anyone confirm?

LC2 repairs

geearr — Mon, 29 Sep 2008 20:17:38 GMT

I have three LC2 units, two of which are working well and one that gave up the ghost a number of years ago. The broken LC2 simply would not power up a lamp under any circumstances and had no control functionality at all. Last week, I decided to explore the insides of an LC2 and took the broken unit apart. After a brief look at the internals, I then put it back together and connected it up once again. Was I surprised when the lamp came on straight away and all of the contact functions were working perfectly. As a last test, I tried the Beo4 but that would only work when the remote was less than 150mm from the LC2.

I have read through some of the previous threads on the LC2 problems but still fail to understand the fundamentals of this unit. How does the contact sensor work? What is the function of the spiders web? What is that small rubber tube with a hole inside for? Is a contact cement needed between the web termination and the rubber tube? What components could be affecting the IR reception?

One of your threads gave a good account of potential interference problems but in this case, I cannot see that this is the issue. Two of the three LC2’s are working well all of the time and the Beo4 range is huge.

Can anyone throw any light on these problems, preferably using simple terms that everyone can understand. I would really like to get this unit working again if it can easily be done. Most of the functions appear to be working and all I have to do is boost the IR reception.

Thanks for your help

Geoff