BeoLab 8000: auto standby OFF > ON > OFF > ON repeatedly at RCA/Line IN

[KolfMAKER]

I have one BeoLab 8000 (serial 16xx) that has a strange problem.

What happens & problem description
I use an audio source connected to the RCA/Line IN input. When starting music it switches from stand-by to On, just as it should.
When I end the music, it in most cases also goes back to stand-by/Off.
But …
After a while (which means starting and ending music several times) it switches like this:

1. It goes OFF > ON > OFF > ON > OFF and then stays OFF. Or …
2. It switches OFF > ON > OFF > OFF etc. repeatedly.

Speakers noise/hum/buzz

From the speaker drivers I hear no noise, hum, buzz or any disturbance. They are quiet, only slight noise when one puts his ear in 5cm range of the driver.

Testing & auto stand-by behavior (in RCA)

I noticed that the time when the auto stand-by switch becomes active, changes when repeating start & stop playing music. So first it goes back into stand-by after 2m:45s, but this time becomes longer after starting and stopping music several times after each other. At some point it takes over 4 minutes, which to my experience is quite long.

The error switching (OFF > ON > OFF > ON, …) sometimes happens after 2m:20, and sometimes after 4m:15s.

Switch from RCA to PL

When the RCA input is active and the auto stand-by switches OFF > ON repeatedly, and when I then push the RCA switch into the PowerLink position, I hear a BUZZ coming up to some point, and then the speaker switches to stand-by/Off (and stays OFF).

• What does this mean?

PowerLink & Auto stand-by tested

Tested with a BeoSound as source, connected via PowerLink. When music is stopped and the BeoSound is being switched off, auto stand-by immediately goes to OFF.

PL/RCA switch

• When pushing the PL/RCA selector switch to a different position, electric noise can be heard.
• After cleaning this switch with Tuner600 (4 times), the electric noise when switching is much less.

 

What I checked/did

• I did find some dirt and solder particles on PCB05 and PCB02. I cleaned those.
• On PCB02, PCB05 and PCB06 I re-soldered several pins/components and connectors.
• After this, with the speaker lying open on the work bench, I got it into a working state. So, auto stand-by had no issues.
• Next, I placed the AMP/PSU part back into the speaker casing, and I did the same with the speaker panel. Though I had the speaker panel standing open. Also in this case, auto stand-by had no issues.
• Then I put the speaker panel inside the speaker casing, and the auto stand-by started going OFF > ON >OFF> ON repeatedly again. It continued like this also after fixing all screws in the speaker and in the AMP/PSU panel.

After cleaning, checking for dry solder joints and re-soldering again, I found the speaker to be more stable. I repeated this test 14 times:

• From stand-by mode, start playing music, via RCA input, and stop the music.
• This worked well 13 times.
• In all 13 cases the speaker switched ON at starting music, and switched back to stand-by after stopping music.
• The wait time until switch back to stand-by was varying, between 2m:15s and 4m:17s.
• After the 14 time, the speaker started to repeatedly switch again: OFF > ON > OFF > ON > …

Question

• Since this speaker works partially ok, but sometimes not, could there be anything wrong with grounding?
• What should I check or fix?

Location: The Netherlands

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