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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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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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ALF
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ALF replied on Thu, Jan 26 2017 12:19 PM

At this point in time I am following Menahem's restoration of a BM4400 as there are no other ''takers'' :-)

The circuit diagram shows diode 5D106/206 but this oneis nowhere to be found on the topoghrapic map

Of components.......am I going blind ??? Or is this a mistake in the SM ?

Martin mentioned a diode in the power amp section that isn't included in the SM but quite obvious on the board????  Where is this mystery diode ?

I dis-soldered all power-output transistors as one blew up in the previous test.

The overload bulb still comes on briefly and the relay clicks after all the component replacements

In the power amp section......!

Next step will be checking the 'fault switch circuit', in particular IC3.

I also noticed BD-165s were installed without a mica foil - is this correct ??

Thank you should you reply with some pointers

Cheers

ALF

marc
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marc replied on Thu, Jan 26 2017 1:08 PM

Alf,

I always replace the tips with 142 and 147's, which can handle a little more voltage, just to be safe.

Craig
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Craig replied on Thu, Jan 26 2017 1:13 PM

Alf...

Gday!......I have just replaced the BD-165 on my current restoration project and it too was installed without a mica foil, I'm assuming there is no requirement for one. I have also replaced all power output transistors, even though it now looks very likely that I didnt need to as the fault now appears to have been a broken track due to a crack in the PCB, in finding this I blew a diode which Martin advised will require a whole bunch of components replaceing, it may be worth noting that my overload relay energised and isolated the 35v rails after I had shorted the diode, previously the relay was not energised.....therefore it may be that even though you have changed all the power transistors you may also, like me, have to replace all the components that Marin has advised for my issue......see my basket case thread for the list of parts. As for the mystery diode I havent come across it...this evening I expect to complete my component replacements then I will double check the orientation of each one before I power up...its so easy to install a diode or transistor the wrong way round......a moments loss of concentration is all it takes....I will look for the mystery diode at this point.

ALF
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ALF replied on Mon, Jan 30 2017 2:01 AM

Hi Craig,

Many apologies for my late response - many thanks for taking an interest in my ''BM4400 project''.

Well, as said earlier I did replace almost all transistors in the power-amp-section as I could not see the point of desoldering, checking and putting them back applying renewed heat-stress.

Changed pretty much all that was on your list - its nice when there is some guidance from ''above'' :-)

I will next draw my attention to the fault switch and overload circuit - just to be safe. Looking back at

All the parts I have replaced so far one could argue for buying  good example of a BM4400 working if

It wasn't for all the fun !

I can't agree more with you when it comes to chasing orderring and waiiiiiiiiting for those parts - located

In Perth-west australia you have next to no chance of finding 'vintage' components !!! I can hardly remember when I started work on the BM4400 ?!!

There is the issue with testing using a dim-bulb-tester and I have decided to build one......finally.

So, there goes some more time again and perhaps I will eventually succeed with some help from

Sympathetic forum members  many thanks again - I will be back !!

ALF

ALF
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ALF replied on Mon, Jan 30 2017 2:16 AM

Thanks Marc,

Tip142 & 147s  are on their way :-)

Hopefully no faked parts (again)

ALF

 

 

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

ALF
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hi craig,

thanks for your reply - your ''mystery diode'' isn't present on my BM4400 board !

the only thing I could imagine that this diode had been ommited by B&O in later factory runs without any service infos ?!

martin - should he read this - might know more as he commented once on that diode !!

in my original service manual it is printed in the circuit diagram but not in the topographic chart.

the only diode visible on the solder-side of board #5 is pictured in my photo and isn't mentioned anywhere ??

take a look at the fotos - I have to do this in 3 separate steps

ALF


ALF
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second pic showing the topographical chart and D106 is nowhere to be seen around TR120 !!


ALF
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look at pic 3: the only diode on the solder side of board #5 but not mentioned anywhere in the SM:


ALF
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pic 4 has a better view showing D104 between TR115 and TR116  while D106 is near  the base of TR120 ????


Craig
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Craig replied on Tue, Jan 31 2017 7:51 AM

Alf

Thank you for the detail regarding D106, clearly your circuit diagram is a more up to date revision that that which I am using. I had identified this diode and marked it up on my thread (got it right second time around) I still don't understand what its doing in there or why it appears in some units and not in others, I have been using Farnell element 14 for my parts, they supply most components but not all...cant be easy for you to get things out there on the other side of the world......have you considered emigrating to the USA, it would seem they are welcoming people with open arms of late ;¬) 

ALF
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ALF replied on Tue, Jan 31 2017 8:53 AM

It is on the rare side to find parts here locally for these vintage hifi components !

Because of the rather poor quality of the SM scan on the site I had decided to buy the 'original SM'.

I am somewhat puzzled about that diode business ........ whether it would help or assist  me  in nailing

The problems on my BM4400 is perhaps not very likely ?! 

The un-annouced design change in the circuit seems for likely or a simple printing error ?!!

Once the fault-switch and overload-section have been under the microscope i shall decide whether or

Not its time to install a full set of new output transistors, risking a new test. They are not exactly cheap

These TIPs.

Several close inspections under the magnifier reveiled no cracks of the circuit board either !!

The DBT will speak soon :-)

ALF

Craig
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Craig replied on Tue, Jan 31 2017 11:33 AM

Alf

Make sure you replace/check all the components identified in Martins list, the diodes and resistors are of equal importance to the output transistors, as I discovered recently my issue was a poor connection somewhere on one of the components identified by Martin...as I removed and checked each component in turn before powering back up I don't know which one was causing the problem......I checked the readings across the pins on the TIP's with the readings I was getting measuring across new ones and as they where the same I replaced the old ones.....which turned out to be a good call.

On a previous restoration I was stupid enough to loosen the securing nut holding OIC203 to the heat sink, this resulted in the transistor overheating and shorting out, martin recommended the following:

 


Replace:

0IC200, 0IC201, 0IC202, 0IC203
TR220
R277
R276

C238

At least check (ideally replace):
0TR200
TR215
TR216
TR217
TR219
D204
D205
R271
R272
R278
R279

Bear In mind the above numbers are for the right channel and the following for the left channel.

This list is different to the one recommended in my thread for shorting to ground the base of TR114 which is as follows:

If you grounded the base of TR114 in the DC offset circuit, the following components would be in question
for replacement or at least a good check:
D100
D101

D102
D103
TR112
TR113
TR114
TR115 (... and further outwards)
Also OTR100 and TR119
Depending on the condition of TR112 and TR113 perhaps TR11 in the overload circuit
could also be of interest.

I suppose it was only a very brief ground contact, else resistors such as 
R156
R157
R159
R166
R168
would also need checking

 

I know it’s a lot of soldering and checking, but I went through both lists…..just get yourself a case of “tinnies” in the fridge and go for it ;¬)

ALF
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ALF replied on Wed, Feb 1 2017 9:20 AM

thanks CRAIG,

It is not that much to check/replace considering the time I have spent already - a few more resistors and diodes and the big ones - the TIPs

finally made up a dim-bulb-tester - and I was hoping to get some clear indication of 'fault or no fault'

but.......it lights up briefly and goes out and so far never stayed on ?!?!

that is unexpected as I was hoping the DBT would clearly indicate a short ???

at the same time the overload-light does not always come on  when FM or any other key is activated??? while I am writing this there are no out-put TIPs installed/connected, just P11 and P12 is connected !

there is still the fault-switch and overload-circuit I want to check and a handful of Rs and diodes to be replaced before I dare to install and connect the out-put TIPs.

ALF

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