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BG4002 Type 5503 Bridge Rectifier

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ALF
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ALF posted on Sun, Dec 18 2016 4:05 AM

greetings all :-))

I am sitting over my "special friend" the BG 4002, not working......

Looking at the circuit diagram it should have 41V DC before OTR1 at 'OFF', 35V DC at 'ON'

It also lacks the 22.8 VDC supply voltage, measuring about 3 V DC lower as it should !!!!

Incoming V AC at OD1 is 33 VAC and outgoing 38VDC  - is it a fair assumption that OD1, the bridge rectifier

might be faulty ??

according to the parts-list it is a B80 C2200 - available would be B80 C3700/2200 as replacements ?!

in case my assumption is correct could I use a B80 C5000/3300 as well ?

thank you kindly for your input

ALF

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Dillen
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Dillen replied on Sun, Dec 18 2016 7:56 AM

The low voltage is most likely because of a high load somewhere.
Remove the load and measure again.

The rectifier is just four diodes - why not just check if they are all there?
Or put a scope across the filter capacitor and see if the ripple is 50Hz or 100Hz and all pulses are of apprx the same peak voltage.

Martin

ALF
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ALF replied on Mon, Dec 19 2016 10:02 AM

The diodes seem all there.

ripple is between 400-600 mV - no specific frequency shown on the scope

however I stumbled into a strange finding:

when disconnecting the platter motor from ground I measured across the 'smoothing caps' (2 x 4000uF)

OFF-mode  41.6 V

ON   mode  38.5 V   instead of 35V

V      mode  35.6V    instead of 31V

the carrige moves across, 33rpm speed is on  and the arm lowers automatically at 30cm record position

I can measure the amplifier output of 11.2 V  and the 22.8 V supply rail is at 22.6V - these measurements occur  with platter motor disconnected !!

re-connecting the platter motor  prevents the automatic arm lowering and 33 speed and shows the 22.8V supply rail at about 19.8V ????????

what is happening here

 

ALF
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ALF replied on Wed, Dec 21 2016 2:04 AM

Speechless ? Clueless ? YES !

Looks like I am not alone ??

I can confirm it is not the rectifier nor is it a faulty platter motor as I did change-over the motor.....

Same outcome !

The million-dollar question remains unanswered - why the voltage drop or current-leak ?

Prize-money after this week's lotto-draw :-)

ALF

Jim Carr
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I would check the transistors OTR 2 & 3. With the motor disconnected they will not draw as much current but could break down with the motor connected and increased current draw.

ALF
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ALF replied on Tue, Dec 27 2016 10:24 AM

thanks for your suggestion Jim,

already replaced both transistors :-) but:

no change I am afraid, unless those parts I received were faked parts ?!

simply don't get it - just for "good measure" I am going ahead and replace the rectifier as

only the OFF voltage showed about 41VDC - ON at 38VDC and V mode at 35VDC are way to high......

there must be a simple reason for that, or mustn't it ??

cheers

ALF

 

Dillen
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Dillen replied on Tue, Dec 27 2016 10:41 AM

If your Beogram has a 2,2uF tantal capacitor on the board under the
operating panel, I suggest you check it and the related diode.

Martin

ALF
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ALF replied on Tue, Dec 27 2016 12:54 PM

Negativ Embarrassed

Diode yes plus a 100uF/25v cap and the muting relay........but no tantal 2.2uF.

ALF

marc
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marc replied on Mon, Jan 2 2017 8:01 PM

Hi Alf,

Reading up on tour post my initial thought is that the motor is drawing to much power, could that be the cause of the problem?

searching on the net i found this:

http://beolover.blogspot.nl/search/label/Beogram%204002

ALF
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ALF replied on Thu, Jan 5 2017 6:30 AM

Marc,

I did change-over the motor to eliminate it as a possible source of the problem.

So far not even our truly treasured 'B&O super guns' provided a promising lead - that is the disappointing

Part - the good part is the 'brain-storming session' is still open and the best is it is 'free entry'

excluding Drinks :-)

I am aware how difficult a remote diagnose is without having that table on the workbench, but......

The devil is hiding somewhere !!

ALF

Jim Carr
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Have you checked the 2 caps for the motor OC3 & OC4?

Dillen
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Alf,

Electronics mechanic is a 3½ year long education with several school levels etc.
Once educated, you can go out and build up experience.
Repairing the older B&O things can be tricky, it's far from any run-of-the-mill "Whatsthebrand" stereo and
it often takes a rather high level of experience and practice to nail problems "just like that".
Don't expect to be able to repair any old fault in any old B&O just because you went to tech school.
Beogram tangentials can be some of the more technically "nasty" ones due to their circuitry and their
combination of mechanics, electronics, switches, optos, sensors etc.
Combinations for which there are no school, no classes or education.

Even some experienced repairshops reject repairs to these decks because they find them too
complicated, involved and/or time consuming (and/or difficult to source parts for).
And by their nature most decks will need a more thorough restoration rather than simple repairs by now -
which only makes matters worse.

Here in the forum we can give you some ideas and tips based on the info, descriptions and symptoms you
provide, - we enjoy doing that - but we can only get so far and we cannot educate you or give you
the instruments, skills, tools etc. it takes to "just do it", let alone provide you with the
difficult-to-explain "sense and feel" for circuits and mechanics that's often a key factor.

The problem in your deck could easily be something simple - it probably is, but how do you know where
to look and how do we know where to ask you to look for us.

There is no doubt in my mind, that I would be able to repair your Beogram if I had it on the bench here -
and so would other posters in this thread - but without the sense, touch, listen, feel and smell, I will
have to limit my input to making educated guesses based on previous similar cases etc..
For almost every possible fault you can think of in a Beogram like yours, there could be several possible
reasons - some are commonly known, others rare and again others still to be discovered.

Are these threads about the same deck:
http://forum.beoworld.org/forums/t/15656.aspx
and
http://forum.beoworld.org/forums/t/20454.aspx ?

If so, with all due respect, the problem could have been introduced by you and not be from "natural causes".
When you can no longer assume anything - those are often the more difficult situations.

Martin

ALF
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ALF replied on Fri, Jan 6 2017 2:34 AM

Thank you for the sobering words :-)

Do I detect a hint of critisism ??? Well, I am aware of most of these things - would not cross my mind

To take the table to a repairer as I may even know more about these machines - certainly not the

Run-off-the-mill thing - damn right !!!!

Did I introduce the problem ?? Sorry, I can not answer that ! 

No one should feel under attack by my post - the disappointing part was addressed to the fact the table 

Is still not working but certainly not directed towards any of our experts here - just in case that had been

Misinterpreted !!!!

I got involved with these machines over the last 2 years and learnt a lot during that time considerring

From whereI I started from - thanks to interest, initiative and help from knowledgable forum members.

I intend to further develop and any help is always much appreciated :-)

It is a desert here in repair-availability terms - there is no other way except throwing out these lovely

Machines - I am not going to do that.

Cheers ALF

 

ALF
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ALF replied on Fri, Jan 6 2017 4:07 AM

the first post is a mix, the second concerns the same table.

let me repeat what the current situation is:

you can operate the table perfectly without connecting the platter motor - spin a record by hand

and everything will work fine till the run-out groove - arm lifts, carriage returns table switches off !

what else can I possibly say ?

I can measure the voltages as per circuit diagram.......the only thing I can see as being odd is a far too

high 'ON' voltage, reading at almost 39 VDC and 'V' voltage, reading at 35.xxVDC plus OC3, reading at

about  5900uF.

ALF

ALF
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ALF replied on Fri, Jan 6 2017 4:24 AM

yes Jim I  did:

OC4 reads about 160uF

OC3 reads about 5900uF

ALF

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