Cant wait to see what happens, I have one BM 3300 waiting, no sound in left channel, and tell your wife that this is important maybe she can help a little

My wife was working longer today so I took the chance to replace the STK. Also checked R123 (which is 99.9 Ohms in my meter), replaced the two fuses and plugged it in. Fuses burnt again immediately so I decided not to do the noise test ... Failure must be something else, not the IC I believe. How about transistors in the heat sink? Couldn't these be the failure in my unit? 

Happy for all replies ;-) 

Don't despair sir!

You now have to methodically check through the system.

If F2 and F3 are still blowing since replacing the output chip,it suggests that D23 the bridge recitifier or OC1 or 2 may be short circuit.These components form the supply to the output stage.

Incidentally,is the unit set to the correct mains voltage?

Nick

Despairing? Me? Never, this unit is worth every drop of sweat to get it back to life ;-) The construction itself is a masterpiece of art and even I never heard how it sounds I'm pretty sure it will be an amazing experience. had a BM1200 years ago and this unit took me to orbit already with its sound ;-) Wonder what the BM3300 will do to me ;-)

Had a look at the 3300 yesterday again and found that the capacitors look suspicious. One is a 6800@40V which seems original and the other one is a 6800@80V. This tells me that somebody was into this unit and only swapped out one of the two caps. Have ordered two new caps with 6800@35V to replace the both. Have no ESR Meter to check them but what I have in my unit just doesn't look right. D23 was checked but I did that in-circuit. Will unsolder it and re-check again out of circuit to be on the safe side. 

Keep you guys posted about progress. I'm happy that I have signed up here. Already went through half the workbench-forum ;-) 

I would suggest fitting 40V or 63V capacitors rather than 35V.
They'd be working too close to their max voltage rating.

Martin 

Hello Martin, 

just checked my order again. I ordered 6800@63V. I was looking at the voltages that go across the PCB and indeed 35V caps would be driven close to their limit. Once arrived I will replace the old ones and re-check again. Makes no sense to me that only one cap was changed ... But tells me that a pro was working on my unit before :D 

Good evening,

the new caps came in today and I just got them in. Still blowing both fuses? I sticked the meter across ground and the contacts of the rectifier D23 and have found about +25V on one contact but nothing on the others. So the voltage comes from one of the caps because the Beo wasn't plugged in anymore at that point. Shouldn't I see negative supply voltage on the rectifier as well? After unsoldering the D23 I found that it looks fine on the meter, no shorts there. Any thoughts?

Many thanks in advance and a great weekend to everyone ;-)

Nick was asking if the voltage selector is set correctly. Don't have a selector but the label on back says 220V @ 50-60hz. Measuring what comes out of the sockets I see 235V there, should be within tolerance.

As it seems as though the unit has received attention from A.N.Other in the past,I wonder if the bridge diode is connected correctly?It could of course be breaking down under voltage,so may still measure ok.

Might be worth trying a new known good one?

Are you fitting 4A fuses for F2 and 3?.

There are some filter capacitors across the supply to the bridge rectifier(C65/66,and another across the positive line (C74)I've never had to replace these,but you never know?

The +33/-33 supply only supplies the main amplifier,although there is a feed to the auxiliary supplies too,but this is protected by a fusible resistor(R110)which surely would have blown if the fault were on that line?

Nick

You've gone quiet sir,was there a happy outcome to your BM3300 problem?

Nick