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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 3rd May 2019, 5:38 pm   #1
dsergeant
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Default B&O 2200 dead

This B&O 2200 music centre has no audio. Fuse 2, which feeds one side of the +/-26V supply to the output amps is blown (fuse 1 OK). Is this likely to be a fault in the output amplifier or possibly a loudspeaker short (I don't have the speakers to check)? I know these are not the best of B&O gear. I have a copy of the service manual. Any guidance welcomed.

Dave
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Old 3rd May 2019, 6:46 pm   #2
Chris55000
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Default Re: B&O 2200 dead

Hi!

Obtain a couple of 12V 5W car sidelight bulbs from your local Poundland, connect one side of fuse 2 to the centre of Bulb 1, connect the metal cap of Bulb 1 to the centre of Bulb 2, then connect the cap of Bulb 2 to the other side of Fuse 2.

Switch the unit on, if either (or both amplifiers!) has a short–circuit or other breakdown across the ±26V L.T. supply, the bulbs will light, whereas if both amplifiers are sound with the fuse simply blowing thro' age or a surge, the amplifiers will still be able to draw enough current to operate in quiescent mode thro' the bulb filaments, giving some sort of audible indication – if you've no suitable speakers to hand already (I think B & O hifi units will safely drive 4 ohms!), either look in your local reusers/recycling centre or charity shops – you'll probably get a cheap one for £2 or so you can try!

If the bulbs connected across Fuse 2 light when the power is switched on, either or both amplifiers has failed, and myself or another Member'll be pleased to advise further!

Please try the above first & let us know what happens!

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Last edited by Chris55000; 3rd May 2019 at 7:14 pm.
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Old 4th May 2019, 6:34 am   #3
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Default Re: B&O 2200 dead

Sounds like an awful lot of work to prove whether there is a short in the amplifiers. I have a Fluke to do that, and quite prepared to sacrifice a fuse to prove the point. I do have speakers (though not with the B&O din connectors), just don't have the ones which were originally used with it to prove whether they have a short. Currently testing with headphones.

Anyway, thanks for your help.
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Old 4th May 2019, 10:01 am   #4
Max Ripple
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Default Re: B&O 2200 dead

The most likely cause of the fuse blowing,is that one of the output amplifier chips(IC100/200) is breaking down under power,so it may not read as shorted when tested unpowered.
Try disconnecting the supplys to the two output chips(pins 5 and 10 on each)then if the fuse doesn't blow,you know where the problem is?If the fuse still blows,then the problem is to do with the power supply (D1,C5,C6) but these should show up with meter testing.

Reconnecting the chips separately will then identify which is the culprit.
Getting another chip (SI-1125H)might be problematic,as new item' s seem to be rare,but there are many enthusiasts out there with salvaged part's available.

Don't give up on the unit,they are neat innovative little unit's and capable of good performance with virtually any other decent 'speakers than the ones that were originally supplied with them
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Old 4th May 2019, 11:26 am   #5
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Default Re: B&O 2200 dead

Hi!

My suggestion was provided because Internally defective power chips don't always show up on a meter as Member Max Ripple suggests, and if the s/c is not an obvious one that proves to be elsewhere other than the power chips, you're not wasting good fuses unnecessarily trying to find it, and if there is a power supply stabiliser (not in the B & O 2200 admittedly but some top end B & O units have one) you're not risking damage to the components in this whilst you trace short–circuit faults!

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Old 7th May 2019, 12:11 pm   #6
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Default Re: B&O 2200 dead

Fault found.
I replaced the 5A fuse in the 28V line. It did not blow but there was a fairly loud hum from the headphones indicative of an overload. The left hand amplifier IC200 got noticeably warmer than the other one. Checking then showed a direct short between pin 8 (-28V) and pin 9 (output) on that module. The right hand amplifier IC100 seems OK.

The SI1125H though as suggested may be hard to source. My quick search showed it available at £25 from China or £70 from Donberg. Anybody know anywhere cheaper?

Dave
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Old 7th May 2019, 1:27 pm   #7
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Default Re: B&O 2200 dead

I have a stock of the SI1125H hybrid amplifier chips for those for a tenner each including UK P&P. Send me a PM if you are interested.

B&O abandoned stabilised power supplies for output stages in the 60s, they were mostly for basic units with fragile Ge output transistors (900, 1000, Beocord 2000 series, Beogram 1500 etc). The only top end design that had one was the mighty Beolab 5000. The Beosound Century (hardly a top end unit!) used Class G techniques so it looks as if the power supply to the output stages is stabilised, although of course it isn't.

Last edited by Studio263; 7th May 2019 at 1:48 pm.
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Old 21st May 2019, 4:52 pm   #8
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Default Re: B&O 2200 dead

Thanks to the replacement chip from Studio263 the faulty left hand amplifier is now working. Unfortunately it seems the right hand one is also faulty, just a low level hum coming out of it and voltage checks show the output is sat at 10V. Is it normal for both amps to fail? I am reluctant to deplete Studio263's stock, it can't be infinite.

Dave
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Old 23rd May 2019, 6:33 pm   #9
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Default Re: B&O 2200 dead

Dave,

Congratulations on having one channel going.
Possibly, as you indicate the other output-IC may also be toasted.
There may be a perfectly good reason for the IC's to break down.
The reason being that the surrounding electrolytic cap's are deteriorating, causing instability and self-oscillation in the amp's.
I wouldn't just replace the broken IC's w/o replacing the cap's at the same time, as otherwise the new and fairly priceless chips could face a very short life in service.
The cap's to be replaced are, see the attached schematic:
C1, C2, c103/C203, C104/C204 & C105/C205

Rgds,

/Torben
Attached Files
File Type: pdf Beocenter 2002 Type 2101_Output-Amp.pdf (278.1 KB, 76 views)
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Old 24th May 2019, 1:33 pm   #10
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Default Re: B&O 2200 dead

If there's room, a couple of the generic LM1875 20W amplifier kits could be a cheap get out of jail card. Depends whether form or function takes priority, I guess.
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Old 25th May 2019, 10:04 pm   #11
Studio263
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Default Re: B&O 2200 dead

Quote:
Originally Posted by dsergeant View Post
I am reluctant to deplete Studio263's stock, it can't be infinite.
I've got loads, PM me if you need another one. Don't bother messing about with the capacitors, there won't be anything wrong with any of them. It was probably someone making a mess of extending the loudspeaker cables that ruined the original ICs.
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Old 26th May 2019, 6:40 am   #12
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Default Re: B&O 2200 dead

Thanks Studio263, I will take up your offer again. It is as I suspect, an accidental short in the speaker cables caused the first chip to blow and then the second one died as it was lacking one of the supplies so put dc across its speaker. With dc coupled speakers anything can happen. The capacitors look fine, propably do a quick check with my Bob Parker ESR meter.

Dave
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Old 3rd Jun 2019, 5:54 pm   #13
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Default Re: B&O 2200 dead

With the second SI1125H fitted this unit is now up and running again. Thanks for the help.
Dave
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