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Beomaster 5500 humming in standby and turned on

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nht posted on Sun, Jan 3 2021 1:51 PM


I hope you can help on this one. I am the otherwise satisfied owner of a Beomaster 5500, but I have an issue with the device humming while plugged to the mains power. Nothing goes into the speakers, but the humming is quite annoying.

My best guess is that the noise is coming from the transformer. Can you help me on how to "kill" the humming?

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Keri replied on Sun, Jan 3 2021 6:54 PM

I don't know what your level of ability is but here is my suggestions.

First, unless you are actually working on it to repair this, immediately unplug it from the mains!


The Beomaster 5500, like the BM5000 that preceded it as well as several other models all utilize a similar standby system which is normally silent.

The Standby mode in these systems utilize a separate low voltage power supply for Standby and some other functions, while the Main power system mostly powers up the amplifier and tuner sections.

By the way, on the BM5500 the Main power runs at +/- 40VDC (80V total) at considerable amperage with two large reservoir capacitors, so it is easy to seriously damage things by poking around with metal tools. 

So, on these systems, the Main power is switched OFF by a relay.  Yes, the relay switches the high current +/- 40V system OFF when energized.  This relay, 2RL1, is operated by transistor 2TR19 which in turn is controlled by the microprocessor system. (9IC1, I think). All of this is powered by the low voltage Auxiliary power supply.

As this Auxiliary power supply is energized at all times when the Beomaster is plugged in and under considerable load holding the Main relay OPEN, the power supply components and the main relay will degrade over time.  

Three systems I have worked on, a BM5500 a BM5000 and a Beocenter7700 have all had seriously degraded main relays, especially the BC7700 where the relay completely failed partially shut, resulting in damage to the amplifier section, noise and a system that would not shut off.

In short, someone needs to carefully examine your Beomaster and replace degrading parts, with particular scrutiny given to the Auxiliary power system and Main relay.  Alas, if the system is making noise while in Standby, damage or degradation to other sections of the unit is also likely.  The good news is, these systems are very repairable.

As the BM5000-7000 series tends to run hot, a bulk replacement of electrolytic capacitors execpt for the very large ones is probably a good idea along with checking the cooling fan but I would advise you to find out what all is wrong and repair it first.

Good luck and Welcome to the Forum!


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I'm not very good at English either! Maybe someday I'll find a language I'm good at?

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nht replied on Mon, Jan 4 2021 9:10 PM

Hi Keri

Thx for the description of system and the welcome.

I will have a look inside the BM5500 to see if I can identify the component(s) making the noise. Doing a little soldering and change simple parts would be no problem, but if it is getting more advanced I will take it to the repair shop. 

I will give a note once I cleared it out (or is left with new questions).

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Copenhagen / Denmark
12,340 Posts

Replace the transformer mounts as the first thing.
They will have hardened by now, most likely to the point of falling apart when touched.


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