[Bilfeldt]

Hello all,

I’ve rather recently taken over a Beosound 3000 system with the Beolab 4000 speakers, which now makes the home office look and sound nice.

Ever since I took it over there has been the usual issue with the glass doors, which did not exactly open smoothly. However, I also noticed that when opening the doors, the motor kept running even after the doors were fully open (stopping based on timer time-out rather than detecting open doors).

So, I started by removing the worst dust from the interior of the BeoSound, cleaned up the rails, applied a small amount of liquid silicone-based grease, and replaced the drive belt to the motor. The doors are now opening and closing very smoothly. So far, so good …

But the motor still keeps running after the doors have opened, making an awful noise and, given the new belt, I suspect also putting quite some load on both motor and the nylon gear wheels. Having looked at the schematics in the service manual, it seems that the BeoSound 3000 uses optical sensors and logic to determine if the doors are open.

Before firing up the oscilloscope and probing around (I guess the “OPEN DET!”-signal is the place to look), I was wondering if any of you guys have had any experience with this issue:
Is it likely to be faulty sensor diodes, the sensor circuit (transistors/op-amps) or am I overlooking something here?
There is no dust covering the diodes now, but I have not cleaned the plastic front panels covering the diodes and PCBs; could this cause unintended reflections and cause the faulty open detection?
Or am I simply on a completely wrong track assuming that these diodes are actually responsible for the “Door Open?”-detection?

The power supply capacitors seem original but there are no issues in CD playing, IR remote functions or anything else, so I would not suspect any power supply failures.

I really appreciate any input on the matter.

Thanks!

[Guy]

According to this thread there is a little switch that possibly has dirty contacts: https://archivedforum2.beoworld.co.uk/forums/p/45201/326714.aspx#326714

The photos are missing, but the video in the last post still works. I think that you can just about make out the switch between the large white cog and the metal plate about 1:20 mins into the video.

EDIT: Here’s a direct link to the video:

[Guy]

I just had a look at the service manual, and the Clamper and Doors switches are shown as part of the ‘Display and Keyboard’ circuit diagram on page 2.25.

[Bilfeldt]

Brilliant! I actually (almost) followed the video when changing the belt but didn’t really pay any further attention to the mechanical switch (nor did I notice it on page 2.25).

But I followed your suggestion and after cleaning the switch properly, everything seems to be working perfectly again.

Thank you, @Guy – and happy new year!

[Guy]

Great news – thanks for letting us know that the fault is cured!

And a Happy New Year to you too! ??

[Author]

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