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Beomaster 4400 - recycling bin or repair ??

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ALF
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ALF posted on Fri, Jan 20 2017 10:03 AM

greetings all,

I have been working on a resurrection project with my BM4400 DOA!!

what happened in the meantime:

replaced all electrolytic caps plus some dead bulbs - nB.: the FM signal-strength is not illuminated no does it show any sign of life - both red tuning indicators however work

replaced the big 10000uF caps

replaced both out-put trimmers R177/277

replaced both pairs of the wirewound resistors R178/179 and 278/279

replaced all TO-92 transistors in the power-amp section except 0TR 100/200

replaced all TIP-141/146 pairs.......faked parts ???????

some work as you can imagine.....

to the test:

one big bang and the TIP146s literally exploded !!!! quite frightening !!

meaning: there is something else terribly wrong ????????????

+35V and -35V is there as well as 15V.

can somebody shed some light on this and give me some pointers ?

after all this work it would seem such a waste to just recycle the unit

cheers ALF

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Craig
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Answered (Verified) Craig replied on Mon, Jan 30 2017 9:42 AM
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Alf

I did manage to locate the mystery diode, see my basket case thread, don't know what it does however...just that it's there. It's probably not much comfort to you to discover that I have been able to sort my particular issue and can now get on with closing it out....It has also been a longer exercise than I expected at the start.....but very satisfying in the end....keep at it.

Craig

Søren Mexico
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Verified by ALF

The DBT behavior is correct, it lights up briefly and then stays out if there are no shorts, it will stay on if there is a short and therewith protect the BM

Collecting Vintage B&O is not a hobby, its a lifestyle.

Craig
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Answered (Verified) Craig replied on Wed, Feb 1 2017 2:04 PM
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Alf

Be sure to check the way the TIP'S are connected in each case, as Martin advises it is very easy to miss the fact that two have the connection wires crossed over and not in line like the others...see my basket case thread for the details, also the BD165 (OTR100) that I fitted needed to be installed "face to heat sink" as the pins where opposite to the one I removed.

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Søren Mexico
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Verified by ALF

The DBT behavior is correct, it lights up briefly and then stays out if there are no shorts, it will stay on if there is a short and therewith protect the BM

Collecting Vintage B&O is not a hobby, its a lifestyle.

Craig
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Yarm, United Kingdom
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Answered (Verified) Craig replied on Wed, Feb 1 2017 2:04 PM
Verified by ALF

Alf

Be sure to check the way the TIP'S are connected in each case, as Martin advises it is very easy to miss the fact that two have the connection wires crossed over and not in line like the others...see my basket case thread for the details, also the BD165 (OTR100) that I fitted needed to be installed "face to heat sink" as the pins where opposite to the one I removed.

ALF
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ALF replied on Thu, Feb 2 2017 8:13 AM

That's right

but

in case of a persisting short wouldn't we have the fault-switch, triggering the relay to cut the power to the power-amp section ??

If that is the case the DBT would certainly go dark again  ?!! And assuming the fault-switch is working correctly !!

Anyhow, that is how I understand it unless I got it wrong.

ALF

ALF
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ALF replied on Thu, Feb 2 2017 12:28 PM

Hi Craig,

Not quite sure I follow ??

I mounted both BD-139 - my replacement for the BD165 - with face up as it should.

Is the marking on the board wrong or is it because the marking/ wires are just the opposite to the BDs pins ??

It should be no problem of crossing those short brown wires towards the pins of the BDs ?!

Please tell me if I am missing the point here ?

ALF

ALF
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ALF replied on Fri, Feb 3 2017 3:32 AM

Yes, assuming the fault-switch works 

But there could be a short somewhere other than in the power-amp-section:-):-)

I guess in that case the DBT would have to light up  !?!

ALF

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