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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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marc
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marc replied on Fri, Jan 6 2017 10:12 AM

Am i glad to just have a BG1900 which speed control relies on 2 magnets inducing a break force on a copper dish mounted on the drive motor!

The only problem with these is that the hinge on the right side breaks...

I went over the schematic, which won't help you because it didn't help me either but still somehow i suspect the motor because disconnected there is no problem and it only appears with the motor connected.

But that's just stupid old me!

what i would do personally is check the current draw of the motor, just to get an idea, shouldn't be more then a couple of 100 mAmps, maybe some one here has a value for you to compare?

But then again, i am not an electronics expert, not by far!

wish you success!

Marc

Jim Carr
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Alf, Does the motor spin when you turn it on and have you looked at the sine wave with a scope?

Also can you check the leakage of the caps? Or any other specs? My schematics show a 4000uf cap for the motor do you have a replacement for your 5900 cap?

ALF
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ALF replied on Sun, Jan 8 2017 10:56 AM

hi Jim,

yes the motor spins perfectly, showing a smooth sine wave - as expected !

I fitted a complete new cap package supplied by Rudy-beolover and it came with a 4700uF instead the specified 4000uF cap - I suspect it is difficult to get in that physical size ?!

I measured mine off circuit at about 5900uF - not quite sure how dramatic that impacts but will replace it with a new 4700 uF cap.

thank you kindly for engaging with that problem - any help is much appreciated.

cheers

ALF

Jim Carr
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Have you seen this site?

http://www.condoraudio.com/wp-content/uploads/Projects/BeoGram-4002-6000-Turntable-Restoration-Repair.pdf

ALF
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ALF replied on Wed, Jan 25 2017 3:14 PM

Yes,

I have seen red and studied that post - thanks:-)

In the meantime I did replace the rectifier - just to be absolutely sure - no change !!

Yes, i barked at the wrong tree.

As this model was a US model I fitted a european transformer with the voltage selector to avoid

Using these step-down transformers but cannot see how this possibly would contribute to the problem ?

Anyhow, nothing is off the table  - and yes Martin, should you read this - I am absolutely convinced

You would have found the culprit and brought back this lovely table to former glory.......but it's a looong

Way from Australia to Denmark !

Still happy to read your ideas, pointers solutions....

Cheers

ALF

Menahem Yachad
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Klaus

Scratching my head, I remember a problem like this on a BG6000 with the AC motor.

There are so many worn-out components on the main PCB, that just a recap is not even the start of an effective solution.

 

Firstly, to confirm that this is the same problem which I had, do the following:

Connect your Beogram via a DimBulb Tester.

The DBT mains bulb (60-75W) should not illuminate (or may be very dim), until the solenoid activates.

Then the bulb illuminates.

If this is what happens, you'll need to replace:

1. these transistors - make sure that you have good replacements and NOT counterfeits TR14, TR15, TR16 - you'll probably find that their hFe's are shot.

2. replace the large motor capacitor with a 220uF BiPolar 105-degree unit. 

3. replace all the poti's

4. Go through the SM adjustment for the "Voltage for drive Motor" (motor phase), using a scope, DMM, AND the DBT.

While adjusting the poti, you can see the immediate consequence of the motor out of phase by the varying brightness of the DBT.

It becomes very clear, very quickly, where the optimum adjustment is.

5. Do the "Detector Arm Sensitivity" adjustment, still with the DBT. You can see where the poti loads the circuit, and the DBT illuminates.

 

Of course, I may be way off base, and the only dead-straight analysis I could give you, would be if the machine was in my lab....

 

Menahem

ALF
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ALF replied on Thu, Mar 2 2017 12:25 PM

Thanks Menahem for your suggestions !

exactly that happened - the moment the arm lowers the dbt comes on and stays on until the arm is raised again!

all this only happens with the platter motor disconnected !!

TR 14,15 and16 have been replaced hFE all good as tested before.

platter motor voltage has been re-checked and adjusted with a scope.

i also replaced OTR4 , the TIP41A  ====>. No improvement !

all potis have also been replaced.

the moment I reconnect the main motor the arm only moves across without lowering plus

the solanoid can not be activated at all.

simple fact remains I can not identify the load that pulls down the voltage ?

i feel the solanoid must draw too much current ?!

i should get 3.5V at E of OTR4 when lowering is activated but only get about 2.45V instead.

i do not believe you way off the mark at all - i just can't see it but believe it will be a simple solution

as it is so often looking back 😳

ALF

Menahem Yachad
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So, you're saying that you install the platter, and then the tonearm won't drop.

I saw that once, and the problem disappeared when I put on an LP.

Couldn't explain it, but it worked. Try it. Just for the heck of it.

 

If not Angry .........

 

Are you certain that TR14, 15 and 16 are correctly installed - NPN or PNP? And, you should have hFe about 250-350.

 

What's the voltage going into the lamp for the tonearm sensor - measured right under the tonearm - when the tonearm is up, and when the tonearm is down?

 

Have you done a solenoid and damper mechanical adjustment, including cleaning the damper cylinder?

The damper could be causing a back pressure.

Keep the DBT connected throughout your testing - the intensity of the lamp will tell you if you're making progress.

Disconnect the solenoid coil, operate the above test as before, measure the voltage, and check if the DBT still illuminates when the tonearm would be down.

If the DBT does illuminate, then the problem is NOT the actual solenoid.

 

Menahem Yachad
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Klaus

 

Firstly, I went back through my 4002 AC notes about 15 years, and found this:

Bus Voltage improvement, after exchanging these transistors (even though the originals were still "OK").

Transistors can check OK under a test meter, and then fail under load.

TR3 TR4, voltage up 0.3V

TR5 TR6, voltage up 0.2V

TR14 TR15, voltage up 3.1V, from 23.7V to 26.8V

TR26 TR31, voltage up 0.15V

 

Also these

D43

8.2 ohm 5W is hot - underside of a smaller PCB, IIRC .

 

R53 R56 hot

 

Your choice if you want to do anything about those - I would recommend it.

 

Next, your old big bad capacitors.

You MUST change them, EVEN IF the capacitance "looks" OK.

I did a BG4000 thread (which I can't find now) showing a DIRECT comparison on my scope of the AC Ripple current of the old original B&O caps, and the same ripple current after installing new capacitors.

With the new capacitors, the ripple current was HALVED.

That's a lot of energy (heat) which was wasted with the old caps.

Nichicon GU is a first-class choice for those 5 big caps, and Nichicon EP for the BiPolar.

There are NO audio-circuits in these BG's, so no need to be crazy and look for exotic audio caps.

Just DO it!

ALF
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ALF replied on Fri, Mar 3 2017 1:26 PM

Let me answer  this reply first.

all I did was without the platter present as no platter should have the same effect for the detector arm as a record present ?!

the two scenarios are with the main drive motor disconnected everything seem to work fine, meaning carriage moves to the 30cm record point

solanoid gets activated and arm lowers - while this is the case the DBT lights up gently and stays on until arm goes up again !

 

the second scenario is with the motor connected - in this case the carriage moves right across and returns to its resting position.

during that move the solanoid can not be activated !

TR14 and TR15  show a hFE reading of about 321, while TR16 shows about hFE  81 - all those are NPN types.

OTR4 - TIP41A - showed hFE of about 31.

with the main drive motor disconnected I get. 22.3V at B of TR10 - motor connected I get 18.4V at B of TR 10

with motor disconnected I get 11.3V at C of TR11 - motor connected I get 8.1 at C of TR11.

the lamp of the detector arm showed 5.7V with motor connected and 6.3 with motor disconnected.

when the solanoid gets activated the damper cylinder moves freely - no sign of any back-pressure at all.

if I disconnect the solanoid coil I can only lower the arm manually but will try !?

ALF

 

 

 

ALF
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ALF replied on Fri, Mar 3 2017 1:33 PM

Menahem,

the big old grey cap package has been replaced - all !!

as for the other mentioned TRs, Rs and D

I am curious and will replace those and keep an eye out for their hFE readings !

will report back about the outcome of the operation.

ALF

ALF
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ALF replied on Thu, Mar 9 2017 7:22 AM

Menahem,

I completed the work you suggested, even included an earlier suggestion of fitting matched pairs of NTE transistors fot the carriage motor to reduce heat.

the outcome of all this is sadly disappointing and after lengthy reflection I have decided to part-out the BG4002.

it was a journey mostly around in circles - enough is enough.

it is very sad as it really is a nice table but unless you swipe the mainboard clean - totally clean I mean,  it would only be more of a mix of old-new

components, introducing new faults.

let me thank you for your input - we can't win them all !

cheers

ALF

Menahem Yachad
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Wow, sorry to hear that.

I wish I could have been able to help you more Sad

Normally, I do a complete overhaul of the main PCB, before starting work on all the mechanical sub-assemblies, which includes checking all the semiconductors, resistors, etc, etc, which are normally bypassed in favour of only a recap. That PCB is much more than just a recap.

Send me a PM of what you're going to part out - I may take some parts.

sonavor
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If the physical condition of the Beogram 4002 is good enough to merit restoration then I would not part it out. The electronics in it are discrete components. There are no complicated, multi-layered circuit boards or anything like that so it should be restorable.

The approach I would suggest is to isolate the specific trouble area and not jump to various things in the turntable. If you have a fully operational Beogram of the same type you could swap parts (just one thing at a time) where you do the swap, check the result and then swap them back. That should result in the problem part being discovered. If you weren't so far away I would offer to do that for you but I think the shipping cost would be prohibitive.

John

ALF
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ALF replied on Sat, Mar 11 2017 3:41 AM

Hi John,

sorry for getting showered with replies, but.......

maybe the parting-out idea was a bit premature, however I have to stress once again that I spent soooo many hours on that BG

my enthusiasm towards that one is at it absolute low point at the moment - perhaps a revisit in good time ??

There are so many new components on that board, which now looks more like a battle ground - the only way seems a complete

clean-up and start from scratch ?

To make decisions even harder, it is in very nice condition indeed which makes it so difficult for me to follow through with the parting-out idea !!!

it is resting right now - main thing is it has a dry roof over its "head"

what a pitty I am so much closer to a desert than a B&O expert !

damn right about the shipping cost though !

kind regards

ALF

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