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Beosound Century door sensor operation

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Centauri
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Centauri posted on Mon, Feb 11 2019 10:37 PM

Anyone know how the Century glass door open/close sensor actually works?  Have a Century 2655 here where the door stays open - on power up, the door will close during the unit's reset, then immediately opens when unit comes ready, and stays there.  All other functions work fine.  In test mode, when door sensor is turned off, door close & open commands work fine, which leads me to believe the issue is with the actual sensor.

I can measure a level change at the photodiode with a CRO when waving the board around near the transmitter leds, but don't see much after the first transistor.  The circuit seems very strange in that the detector output is monitoring the current of the transmitter leds and somehow the receiver is modulating this. The output seems to just stay near 0 volts no matter what happens at the sensor.  Have no idea what the multiple filter stages on the receiver are supposed to be doing.  Anyone know what sort of waveforms I can expect to see through the circuit, or how it is actually supposed to work?

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Bronya
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Bronya replied on Wed, Feb 13 2019 7:33 AM

Hello..I noticed your diagram for the Model 2655.  I have one the same but what I'm wondering if I go & be a silver member will i be able to  download a service manual from Beo World?

Orava
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Orava replied on Wed, Feb 13 2019 9:51 AM

I had similar behavior when door was removed, and after putting it back it did work normally. So it does close the door and if dont regonice door in closed position, thinks something is wrong and opens it, I guess.

 blah-blah and photographs as needed

Bronya
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Bronya replied on Wed, Feb 13 2019 9:48 PM

Thanks, but what i would like to know if I upgrade to a silver member will I be able to get a service manual for my Beosound 2655??

Centauri
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Bronya, suggest start a new thread - above diagram from models 2651 to 2654 service manual easily available on net - google it - close enough to 2655.

Back to original issue, another member suggested C153, but replacing that (and C155 for good measure) made no difference.  Really need to know what is supposed to happen at the output - the labelling would suggest active low for door open trigger, but the output just seems to monitor transmit leds current - if the leds are on (as they are), then the output will be low (as it is).  Is the receiver supposed to cause the transmit leds to flash or something?  Maybe if the output is normally supposed to be low for no sensing, I might have a faulty CPU ...

Cheers

Orava
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Orava replied on Mon, Feb 18 2019 10:15 AM

Do you get signal verifying that door is closed?

For a moment I tought too that my cpu board was faulty on my Century, but after all it was "simple" broken track. Boards are not the best possibly quality on these..

 blah-blah and photographs as needed

Centauri
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Orava, what verifying signal is this?  Trouble is that I do not know what signals I am supposed to see where.

Orava
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Orava replied on Tue, Feb 19 2019 1:31 PM

I might be wrong, but if you check Open Det and Door Open/Closed lines, does it tell anything?

This might be basically movement detector and sorts(filters) signals depending what kind reflection it recieves?

Motor control seems to be on power supply board, that is the very board I had loose track(s).

 blah-blah and photographs as needed

Centauri
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Update: Got the door sensor working.  Couldn't work out the operation as the output is derived from the current through the transmit LEDs - I had made the assumption that if the LEDs are on, the output would be zero, and high if the LEDs were off, which didn't make sense.  Analysing it closer, the transistors Tr37 to Tr39 form a constant current driver set by the value of R252 - under normal conditions the voltage developed across R253 is not enough to turn on Tr40, so the output should be high level.  It would seem that a pulse from the detector via C340 will cause a momentary increase in LED current, which will then turn on Tr40 & give a low level output.  Issue was faulty transistor Tr37, which meant LEDs were full brightness & output locked on door open command.  A lot of time wasted on this.

On another note, does anyone have a photo of the rear of the Century with the rear cover off?  This unit had come to me from another repairer with some bits missing.  There would appear to be some sort of mounting that goes across the back of the CD decoder board that the rear handle / active antenna bolts into, and this part is missing.  Haven't been able to find a drawing or photo of this - if the owner cannot get the missing part from the previous repairer, I may need to fabricate something, and it would be much easier if I knew what the original part looked like.

Thanks

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