Dear all,

My Beomaster 4400 recently became dumb. When I push the ON button, the OVERLOAD brights for a fraction a second (I also can hear a 'clack' in the loudspeakers) and after it is ON (the radio signal strength goes on 4.5 for example) nothing comes out from the loudspeakers.

I also tested the headphones output, but nothing there too (except the horrible 'clack' at ON and OFF).

 Any hope to repair it ? (optically my B&O is in excellent condition, the wood is perfect and I still have the plastic front cover from the 6 radio pre-selections + a nice antenna I bought from a B&O dealer in the 80')

 I'm not a professionnal electronician, but I can recognize transistors, and probably (?) replace a pair... (assuming the problem is coming from the power transistors) if one of you give me some inputs and a straightforward strategy to identify the failure...

Many thanks for your help !

Luc
 

 

 

Well it does sound like a component failure but it could be a number of different issues. I would hope that it is not the transistors but possibly the capacitors or variable resistors that are in need of replacement. However to discover which, you will need to have some testing equipment and the service manual and know what you are doing. It would be beyond my skills (and eyesight!) so I would suggest getting someone to do this for you. The service manual is available on the site to silver and gold members.

Luc,

As Peter suggests, capacitors can never be ruled out.
They are known to cause the strangest faults.

Your Beomaster 4400 goes into "safe mode" because one (or both) of the amplifiers no longer work symetrically.
You could try without speakers (headphones alone) to rule out
faults in the speakers and cables.
If you didn't touch the speaker cables or similar just prior to the fault, I suppose one of the amplifiers have a defect.
I've seen this happen several times with the BM4400 and it's
definitely worth repairing since the problem hardly ever
lies within the extreme output stage in this model
but much rather a small signal transistor in a driver/pre-driver stage
which suggests a somewhat cheaper repair.
The fault could also be in the power supply but it's rare to see.

Without power on the BM you can run an ohm-meter across the transistors in the output stages and look for strange readings or you can take
the tehnician-approach:
(Speakers dismounted for safety)
The channels can be separated from the fault detector circuit by
lifting a resistor. Take a look at the schematics and you'll see what
I mean. This will allow the amplifier to stay powered while measuring.
Bring it up on a variac to limit any shorts and maybe keep the
mains voltage down in the beginning, up slowly, to protect the BM.

With all due respect; If the above makes no sense to you, I suggest you leave servicing to someone else, it shouldn't be a costly repair.

Martin

Peter, Martin

Many thanks for your insights. My BM was first repaired 10years ago (B&O Marseille), and output transistors were faulty (as far as I remember). It needed a second repair 4 years ago only (B&O Aix en Provence -I had moved), that required the big capacitors to be replaced in the power supply.

Martin's suggestions are at the limit of what I can understand and undertake in electronics, but I will try to do something. I have a (rather bad) copy of the schematics.

By the way, the Volume and Balance cursors were very noisy, I should try to clean the contacts following Martin suggestions in another post.

L 

 

Martin

When I tested the phones output yesterday evening, both speakers were disconnected. 

L 

Martin,

A question about the resistance to lift of: I guess they are R46 (left channel) and R47 (right channel) (both 680K).

Is it correct ?

I have a small volt/amp/ohmmeter at home (2Kohms/volt only), and I can access a variac at work.

L 

 

I don't have the manual at hand but I seem to remember that the 680K is correct.
Almost all multimeters have a diode-tester setting.
This would be the best setting to use, though a standard ohm-meter
could give a hint as well.

Martin