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Beomaster 4400 power-amp problems or ?????

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ALF
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ALF posted on Tue, Feb 7 2017 9:46 AM

Hi everyone !

I am in the middle of restoring a BM4400:

So far all electrolytics have been replaced incl the two big ones.

Both output trimmers have been replaced with 25-turn new ones

All output amp TIPs have been replaced with TIP142/147 and The BD-165 with BD-139

And YES,  they were all conected the correct way - even with some of the short brown wires crossed :-)

All TO-92 transistors in the power-amp section have been replaced together with D101,102, 103, 104

IC3 together with TR15-16 and D22 in the fault switch have also been replaced.

TR1 and TR2 have been replaced

A long list of resistors - as suggested by Martin and Menahem - has been replaced as well.

Turning on the unit via, the DBT shows as follows:

Without P11/12 connected the DBT briefly illuminates, goes out, overload bulb does not illuminate, RL1 does not engage.

With P11 or P12 or both connected the DBT briefly illuminates, the RL1 engages, DBT goes out.

What am I missing here ? 

The PCB has been inspected with a strong magnifier for cracks, but 'negative' - no cracks to be visible !!

Is it likely that the RL1 is faulty ??

Replacing so many components was not only easier but in my opinion sensible, as desoldering, testing and

putting them back in would have reintroduced worn-out parts.

Is it worth taking out the RL1 ??

Any help/suggestions is more than welcome :-)

ALF

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Dillen
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Any DC on the output rails?

Martin

Lonnie
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Hi ALF,

I noticed in your picture P1010148 that you may have crossed over the C&E leads from the board to the TIP147 - 0IC202.

The manual shows the layout from the bottom view which has ECB from left to right. When you flip it over to get the top view perspective you will have BCE from left to right. You have B going to B, C going to E and E going to C???? You may need to double check this as the manual may be wrong but also the printed boards are often wrong. If the manual is correct then the leads should not be crossed over. I don't have a BM4400 so I can't do a physical check for you. Maybe someone else can?

Regards

Lonnie

 


Craig
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Alf

As lonnie quite rightly points out....the printed boards and circuit diagrams can contain some inconsistencies and therefore its always best to replace components in the same orientation as they came out, after all they worked  that way for forty years or so, have a look at the picture of one of mine, it shows from left to right OIC201/OIC202/OTR200/OIC203.....unfortunately OIC200 is out of shot, however the important thing to note is the clearly visable crossover of connections on OIC202.


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RaMaBo
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RaMaBo replied on Fri, Feb 10 2017 7:45 PM

Hi Alf,

nearly four years ago Soren Mexico did a similiar job on a Beomaster 4400 having also problems with the Fault Protection circuit and finally managed to fix it:  Sorens Thread

Maybe you should read some of the posts ( okay, maybe pages of posts Wink ) in this thread. It might be helpful to see how he managed to isolate the final failure.

 

 

Ralph-Marcus

ALF
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ALF replied on Sun, Feb 12 2017 2:31 AM

Hi ralp,

I did ideed red through this and other related posts to find pointers, expanations and suggestions......but I am also aware how difficult

 it is to come up with a long-distance diagnose and even a solution of a particular problem.

Discovering an ivisible crack on a solder-joint or pcb track requires some magical skills, experience and luck - some here seem to have those attributes ?!?

Considering the work and hours spent on that receiver I would be lieing not to have come close to throwing in the famous towel !!

There isn't much left in the power-amp section that would make sense to me to replace ?!

I keep asking myself whether something somehow makes contact with the chassis that shouldn't - but I can't see it ?

I keep on it for a little while longer - with or without support.

ALF

Søren Mexico
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I have, with admiration, been following your thread Alf, dont give up now, take a break for a couple of days and start again, my luck finding the failure was comparing right and left channel again and again, sorry I cant help you more, but go on you are very near completion.

Soren

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ALF
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ALF replied on Mon, Feb 13 2017 4:07 AM

Hello Søren,

Thank you for your encouraging words - yes, it has been a struggle so far and I have come a long way looking back at this monster!

I also have been checking, replacing, more checking more replacing but not yet ''home'' !!

Yesterday I started double checking the TO-92 transistors in the power-amp-section for correct 'polarity' and yes, i did discover some errors

I have made which was at last some devlopment and encouragement to carry on - the devil must hide somewhere. :-)

 cap C132 turned out to be the wrong way around as well as 5TR120/119/219 - all TIPs checked out ok and after reading about your

22/22k resistor it showed me again mistakes can be made soooooo easily.

Now off to 'work' for some more checking - I am still convinced it will be just a little thing causing all that stress and failure !

Keep you posted !!

ALF

ALF
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ALF replied on Tue, Feb 14 2017 1:12 AM

A brief up-date :

After detecting a couple of wrongly installed transistors in the power-amp section I turned to one of 'martins list of recommendations' and repaced D105/205 and TR11,12,13 from the overload circuit !

Despite RL1 being engaged the overload light now stays on ???

It is getting more and more ''interesting'' and I wonder what comes up next on the way ?

Only a BG4000 or BM8000 could be more nerv-wrecking !

Back to work unless someone stops me with a constructive suggestion:-):-)

ALF 

ALF
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ALF replied on Tue, Feb 14 2017 5:09 AM

Small success:

Broken track discovered at TR13 - now Overload light works again as it should :-)

ALF

Søren Mexico
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Small details Alf, small details progress go on, I love it

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

Craig
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Craig replied on Tue, Feb 14 2017 11:47 AM

Its amazing the things you find if you step back and take a breath, its very easy to lose concentration for a moment and these components are very small....I installed 2 diodes the wrong way around and it was a couple of days later that I noticed I had the polarity wrong on both of them......fortunately it was prior to powering up....keep at it Alf

sonavor
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It is also another reason to take good, detailed pictures and post them of your work. A number of times I have studied my pictures and realized that I did something wrong. When I'm relaxing at my desk and reviewing things, instead of hunkered over the workbench, the brain processes the information differently.  Just the act of posting pictures and writing up the description makes your brain review your work in a different way that is often helpful.  It also helps to have other sets of eyes look at the work.  I remember one time I had installed a capacitor incorrectly on a Beogram 8000. A Beoworld member spotted it and let me know...and I fixed it. That's a great thing about the forum.

-sonavor

Søren Mexico
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As Sonavor I often go back to my threads and pics away from the workbench, sometimes I just leave it all for a couple of days, and come back with new ideas and a fresh view, as Craig I have several times inverted diodes or transistors in my repairs, at times forgot to solder a leg or two. A couple of times broke tracks desoldering component, and had a long time finding it again

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

ALF
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ALF replied on Thu, Feb 16 2017 5:38 AM

Hello sonavor & søren,

thank you for your replies - shortly i will upload a couple of pics.

i still keep thinking about that thermistor - unusual symbol used in the circuit diagram - and

the protection relay RL1.

can we really rule-out both components ? Sure, it has been explained before that a faulty thermistor

should trigger the faul switch at all times, but........?!?

also, is the RL1 so reliable not to react perhaps over- sensitive ?

i took off the two tuner related boards to check again for possible cracks of board 5, but negative .

again, just thinking aloud !

enjoy the pictures    😩

ALF

ALF
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work impressions - enjoy


ALF
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more work impressions


ALF
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spotted the devil ?


ALF
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he is hiding somewhere !


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