The Workbench

Re: Faulty Beomaster 4400

chartz — Fri, 25 Nov 2011 05:36:41 GMT

Re: Faulty Beomaster 4400

Søren Hammer — Thu, 24 Nov 2011 14:36:25 GMT

That is very good news!

I agree that the tuner of this beast is very well engineered. the AFC-part being very very good. It's a shame that almost all FM stations here only offers super-compressed pop music these days...

Re: Faulty Beomaster 4400

chartz — Thu, 24 Nov 2011 13:47:42 GMT

Still working fine. I pushed it a little and the cooling finns remain lukewarm at best.

Plenty of power, superb sound. The best amp I've got period, all makes considered. Better than my treasured valve amp. And it's got a superb tuner to boot!

Re: Faulty Beomaster 4400

chartz — Wed, 23 Nov 2011 01:25:12 GMT

Well yes the muting circuit works normally. But you're right about the smoke! The relay clicks normally too. An unlucky chain of events I guess...

Now the fffft extinction noise! This is going to be à tough one!

Re: Faulty Beomaster 4400

Step1 — Tue, 22 Nov 2011 20:14:35 GMT

Strange that the protection diode had failed! That would possibly explain the smoke earlier then!

Have you checked the muting circuit and its effect on the amplifier?

Re: Faulty Beomaster 4400

chartz — Tue, 22 Nov 2011 14:19:01 GMT

Frightening stuff.

I was fiddling with the speaker cables (stupid banana plugs, ahem) when suddenly, pop, smoke...

One fresh BC516 darlington gone in smoke, fried, belly-up, kaput. Overload beacon lit.

?????????

Yes, the protection circuit, the one I repaired, bla bla bla.

Thing is, I had forgotten to test the b(beep)y relay diode. It was shorted! At least it proved that the detection circuit worked—it did, since the BC516 fried!—well sort of then!

Anyway, fixed! Phew!

Another lesson learnt, I should have known better, shouldn't I?

Re: Faulty Beomaster 4400

chartz — Mon, 21 Nov 2011 13:00:30 GMT

Thanks Menahem.

Do you have any ideas about the fffft when the receiver is turned off?

Re: Faulty Beomaster 4400

yachadm — Mon, 21 Nov 2011 06:32:38 GMT

Well done!

Those years (IMHO) were B&O's absolute best. They never made better than those.

I've worked on many over the years, but the BM2000, 3400, 4000, 4400 have the best sound of all. No matter the specs, it's my ears that tell me that!

Menahem

Re: Faulty Beomaster 4400

chartz — Sat, 19 Nov 2011 12:38:29 GMT

Beware, those tiny volume and tuning wheels have à tendency to go to funny places... I spent some time looking for one in my workshop!

The two middle screws seem impossible to access, but B&O techs left some space to insert à screwdriver from the bottom, between the different layers of circuits!

And the tuning slider is glued to the string!

Re: Faulty Beomaster 4400

Søren Hammer — Sat, 19 Nov 2011 12:26:32 GMT

chartz:

Søren Hammer:
I left the two under the power switch

So you'll never know what the receiver is capable of! I'm sure these are precisely the ones that affect sound quality the most!

I thougt just the same, but I was not in the mood for playing with free-style solutions! Doing the caps if cleaning the faders need cleaning, as the fascia has to come off when doing it

Re: Faulty Beomaster 4400

chartz — Sat, 19 Nov 2011 11:27:06 GMT

Søren Hammer:
I left the two under the power switch

So you'll never know what the receiver is capable of! I'm sure these are precisely the ones that affect sound quality the most!

Re: Faulty Beomaster 4400

Søren Hammer — Sat, 19 Nov 2011 10:35:54 GMT

Wow, Looking good!

I left the two under the power switch

Re: Faulty Beomaster 4400

chartz — Sat, 19 Nov 2011 09:39:23 GMT

I have now repaired the protection circuit. I didn't want to know, I just replaced the unavailable darlington with a BC516 (thanks Martin) and both BC548s with BC172s.

I've let it on playing for hours. Checked the quiescent current again, and adjusted it to 14 mV finally, as per Martin's advice. The only detail I'd like to solve is that there's a fugitive hissing noise when I switch the unit off on one channel. It goes Ffffft for half a second. That's it. No humming, no hissing. Even the transformer keeps quiet which, as I understand it, is not that common!

The received really sounds great, if possible better that both BM 6000 and 8000... That came as a surprise, and it's rapidly growing on me!

Where's the remote though?

Re: Faulty Beomaster 4400

chartz — Sat, 19 Nov 2011 01:15:31 GMT

Rich:

Hope she "lives long and prospers" for you.

Well done, Jacques!

What's she driving?

Thanks. Driving a pair of MC120-2!

I'd like to find a pair of mint MS100 though!

Re: Faulty Beomaster 4400

Rich — Fri, 18 Nov 2011 17:34:38 GMT

Hope she "lives long and prospers" for you.

Well done, Jacques!

What's she driving?