Hi everybody, i´m competely new here, but i tried to search without results for some help.

I bought a B&O 5000 system (beomaster 5000, beocord 5000, CD50 and beogram 5500). All parts were defect... The cd-player and the cassetter recorder is now ok (new belts only). But the beomaster is still defect, when i connect it and turns it on it shuts down again. It sounds like a short circuit in the transformer, i have measured the power transistors for errors, but nothing there...

The beogram was destroyed by force, is missing the optical arm, so it´s only junk i suppose...

Anyway: 

 When it shuts down theres a big spark on one side of the relay for the power (not speaker relay), both connectors in the relay is burned but zero in resistance, so it should be ok.

 Any suggestions where i can search for errors??

Theres nearly zero in voltage over the big capacitors after it has powered off, the fan turns arund a half turn.

The connection with the remote is ok, it gets information from the amp as well..

 I suppose there is a error in the power amp, but what.... Schematics would help...

Gosh, i really prefere burned components..... 

UPDATE 

 The IC 100 (i think), one of the power transistors get hot :-) , will try to remove it. Have removed the connector from the power amp to the relay, same result.

Best regards

Erik Achrén 

Hi Erik, and welcome!

In wait for the real experts to chime in (I've never been inside a 5000),  I'll tip you that the trimpots that control the idle current of the power amp are most probably bad (R126 and R226, 100 ohms).  This will cause the power amp to draw much more current than it is supposed to, and the protection circuits will shut the amp down sooner or later. If this goes on long enough, the power transistors might be damaged as well (IC100 is one of them).  Don't try reviving the old trimpots, they are trash by now - just replace them (and adjust the new ones to middle before powering up again).

The service manual is available on site, but you'll have to be at least a silver member to access them. Well worth it, if you plan on repairing more B&O in the future!

Thanks for the reply :-) 

That was one of my theories too, have measured it (resistance) and compared it with the other channel, and they are about the same. In the other hand, if it is oxided you´ll never know what happens... 

 Have measured the transistors and they have the same values in place on both channels so they should still be ok.

 I´m gonna have a look in my drawers and try to find a 100 ohms trimpot or two.

I will become a silver member soon, it´s been christmas and my wife is studying, and we have children so the money is needed for other stuff right now :-) 

Tadaa!!

It was the trimpot!! I turned it around for a little while and now it´s working! Noise from the tape inputs in my headphones when i put a skruwdriver in the phono contacts!

Thanks :-) 

I will order a pair of new ones tomorrow.

How do i adjust the idle current??

//Erik 

by the way, with a nice forum like this it´s worth buing defect eqipment, become a silver member and repair the stuff :-) 

Well done! I'll attach an excerpt from the service manual. Since the amp now stays on, replace the trimpots one at a time so you have a better chance of adjusting the new trimpot properly before anything heats up again. They shouldn't end up too far from center position if everything else is working properly.

I don't think there have been many problems that weren't solved on the forum. 

Yes, new trimmers. And do one channel at a time, starting with the bad one to keep the Beomaster from shutting down while adjusting.

Furthermore, if only one output stage transistor gets hot, it could be a sign that it's thermic contact to the cooling fin has been compromised.  The last couple of BM5000's I've had in for service all showed sign of dried cooling paste, it gets hard and loses it's thermic properties. Clean it off and add fresh paste.

Martin

Thank both of you, i will do as you say. I was thinking about repairing it and selling it, but i think i will keep the things instead, i really like the design... And my wife also think it looks pretty cool :-)

Will do a new post about beogram 5500 soon,